Guidance for Industry 

E14 Clinical Evaluation of QT/QTc 

Interval Prolongation and 

Proarrhythmic Potential for 

Non-Antiarrhythmic Drugs 

U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER) 

Center for Biologics Evaluation and Research (CBER) 

October 2005 

ICH 
Guidance for Industry 

E14 Clinical Evaluation of QT/QTc 

Interval Prolongation and 

Proarrhythmic Potential for 

Non-Antiarrhythmic Drugs 

Additional copies are available from: 

Office of Training and Communication 

Division of Drug Information, HFD-240 

Center for Drug Evaluation and Research 

Food and Drug Administration 

5600 Fishers Lane 

Rockville, MD 20857 

(Tel) 301-827-4573 

 http://www.fda.gov/cder/guidance/index.htm 

Office of Communication, Training and 

Manufacturers Assistance, HFM-40 

Center for Biologics Evaluation and Research 

 Food and Drug Administration 

1401 Rockville Pike, Rockville, MD 20852-1448 

 http://www.fda.gov/cber/guidelines.htm. 

U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER) 

Center for Biologics Evaluation and Research (CBER) 

October 2005 

ICH 
TABLE OF CONTENTS 

I. INTRODUCTION (1, 1.2)................................................................................................ 1

A. Background (1.1)............................................................................................................................2

B. Scope (1.3).......................................................................................................................................2

II. CLINICAL TRIALS (2)................................................................................................... 3

A. Overall Approaches to Evaluating Drug Effects on QT/QTc Interval (2.1).............................3

1. Subject Enrollment (2.1.1) ..............................................................................................................3

2. Safety Monitoring and Discontinuation Criteria (2.1.2) ................................................................3

B. The “Thorough QT/QTc Study” (2.2 ).........................................................................................3

1. Design of the “Thorough QT/QTc Study” (2.2.1) ...........................................................................4

2. Dose-Effect and Time Course Relationships in the “Thorough QT/QTc Study” (2.2.2).................5

3. Timing of ECGs in the “Thorough QT/QTc Study” (2.2.3).............................................................6

4. Interpretation of the “Thorough QT/QTc Study” (2.2.4) ................................................................6

5. Alternative Strategies to Assess QT/QTc Interval Effects (2.2.5) ....................................................6

C. Clinical Trial Evaluation After the “Thorough QT/QTc Study” (2.3) .....................................6

D. Clinical Development When the “Thorough QT/QTc Study” Cannot Be Performed in 

Healthy Volunteers (2.4) ........................................................................................................................7

E. Collection, Assessment, and Submission of Electrocardiographic Data (2.5) .........................8

1. Collection and Assessment of Standard 12-Lead ECGs (2.5.1)......................................................8

2. Ambulatory ECG Monitoring (2.5.2)...............................................................................................9

3. Submission of Interval and Waveform Data (2.5.3).........................................................................9

III. ANALYSIS OF ECG DATA FROM CLINICAL TRIALS (3).................................... 9

A. QT Interval Correction Formulae (3.1) .......................................................................................9

1. Population-Derived Correction Formulae (3.1.1).........................................................................10

2. Correction Formulae Derived from Within-Subject Data (3.1.2)..................................................10

B. Analysis of QT/QTc Interval Data (3.2)....................................................................................10

1. Analyses of Central Tendency (3.2.1) ............................................................................................11

2. Categorical Analyses (3.2.2)..........................................................................................................11

3. Analysis of Relationship Between Drug Exposure and QT/QTc Interval Changes (3.2.3) ...........12

C. Morphological Analyses of ECG Waveforms (3.3) ...................................................................12

IV. ADVERSE EVENTS (4)................................................................................................. 12

A. Clinical Trial Adverse Events (4.1) ............................................................................................12

B. Premature Discontinuations or Dosage Reductions (4.2).........................................................13

C. Pharmacogenetic Considerations (4.3).......................................................................................13

D. Postmarketing Adverse Event Reports (4.4) .............................................................................14

V. REGULATORY IMPLICATIONS, LABELING, AND RISK MANAGEMENT 

STRATEGIES (5) ....................................................................................................................... 14
A. Relevance of QT/QTc Interval Prolonging Effects to the Evaluation Process (5.1) ..............14

B. Labeling Issues for Drugs that Prolong the QT/QTc Interval (5.2) ........................................15

C. Postmarketing Risk Management for Drugs that Prolong the QT/QTc Interval (5.3) .........15
Contains Nonbinding Recommendations

1

Guidance for Industry1

E14 Clinical Evaluation of QT/QTc Interval Prolongation and 

Proarrhythmic Potential for Non-Antiarrhythmic Drugs

This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It 

does not create or confer any rights for or on any person and does not operate to bind FDA or the public. 

You can use an alternative approach if the approach satisfies the requirements of the applicable statutes 

and regulations. If you want to discuss an alternative approach, contact the FDA staff responsible for 

implementing this guidance. If you cannot identify the appropriate FDA staff, call the appropriate 

number listed on the title page of this guidance. 

I. INTRODUCTION (1, 1.2)2

This guidance provides recommendations to sponsors concerning the design, conduct, analysis, 

and interpretation of clinical studies to assess the potential of a drug to delay cardiac 

repolarization. This assessment should include testing the effects of new agents on the QT/QTc 

interval as well as the collection of cardiovascular adverse events. The investigational approach 

used for a particular drug should be individualized, depending on the pharmacodynamic, 

pharmacokinetic, and safety characteristics of the product, as well as on its proposed clinical use. 

The assessment of the effects of drugs on cardiac repolarization is the subject of active 

investigation. When additional data (nonclinical and clinical) are accumulated in the future, this 

document may be reevaluated and revised. 

FDA's guidance documents, including this guidance, do not establish legally enforceable 

responsibilities. Instead, guidances describe the Agency's current thinking on a topic and should 

be viewed only as recommendations, unless specific regulatory or statutory requirements are 

cited. The use of the word should in Agency guidances means that something is suggested or 

recommended, but not required.

 

1 This guidance was developed within the Expert Working Group (Efficacy) of the International Conference on 

Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) and has been 

subject to consultation by the regulatory parties, in accordance with the ICH process. This document has been 

endorsed by the ICH Steering Committee at Step 4 of the ICH process, May 2005. At Step 4 of the process, the final 

draft is recommended for adoption to the regulatory bodies of the European Union, Japan, and the United States. 

2 Arabic numbers reflect the organizational breakdown in the document endorsed by the ICH Steering Committee at 

Step 4 of the ICH process, May 2005. 
Contains Nonbinding Recommendations

2

A. Background (1.1) 

An undesirable property of some non-antiarrhythmic drugs is their ability to delay cardiac 

repolarization, an effect that can be measured as prolongation of the QT interval on the surface 

electrocardiogram (ECG). The QT interval represents the duration of ventricular depolarization 

and subsequent repolarization, and is measured from the beginning of the QRS complex to the 

end of the T wave. A delay in cardiac repolarization creates an electrophysiological environment 

that favors the development of cardiac arrhythmias, most clearly torsade de pointes (TdP), but 

possibly other ventricular tachyarrhythmias as well. TdP is a polymorphic ventricular 

tachyarrhythmia that appears on the ECG as continuous twisting of the vector of the QRS 

complex around the isoelectric baseline. A feature of TdP is pronounced prolongation of the QT 

interval in the supraventricular beat preceding the arrhythmia. TdP can degenerate into 

ventricular fibrillation, leading to sudden death. 

While the degree of QT prolongation is recognized as an imperfect biomarker for proarrhythmic 

risk, in general there is a qualitative relationship between QT prolongation and the risk of TdP, 

especially for drugs that cause substantial prolongation of the QT interval. Because of its inverse 

relationship to heart rate, the measured QT interval is routinely corrected by means of various 

formulae to a less heart rate dependent value known as the QTc interval. It is not clear, however, 

whether arrhythmia development is more closely related to an increase in the absolute QT 

interval or QTc. Most drugs that have caused TdP clearly increase both the absolute QT and the 

QTc (hereafter called QT/QTc). Documented cases of TdP (fatal and nonfatal) associated with 

the use of a drug have resulted in the withdrawal from the market of several drugs and relegation 

of other drugs to second-line status. Because prolongation of the QT/QTc interval is the ECG 

finding associated with the increased susceptibility to these arrhythmias, an adequate 

premarketing investigation of the safety of a new pharmaceutical agent should include rigorous 

characterization of its effects on the QT/QTc interval. 

B. Scope (1.3) 

The recommendations contained in this document are generally applicable to new drugs having 

systemic bioavailability, but may not apply to products with highly localized distribution and 

those administered topically and not absorbed. The focus is on agents being developed for uses 

other than the control of arrhythmias, as antiarrhythmic drugs can prolong the QT/QTc interval 

as a part of their mechanism of clinical efficacy. While this document is concerned primarily 

with the development of novel agents, the recommendations might also be applicable to 

approved drugs when a new dose or route of administration is being developed that results in 

significantly higher exposure (i.e., Cmax or AUC). Additional ECG data might also be considered 

appropriate if a new indication or patient population were being pursued. The evaluation of the 

effect of a drug on the QT interval would also be considered important if the drug or members of 

its chemical or pharmacological class have been associated with QT/QTc interval prolongation, 

TdP, or sudden cardiac death during postmarketing surveillance. 
Contains Nonbinding Recommendations

3

II. CLINICAL TRIALS (2) 

A. Overall Approaches to Evaluating Drug Effects on QT/QTc Interval (2.1) 

Drugs are expected to receive a clinical electrocardiographic evaluation, beginning early in 

clinical development, typically including a single trial dedicated to evaluating their effect on 

cardiac repolarization (“thorough QT/QTc study”). Factors that could reduce the need for such a 

study include the inability to conduct the study in healthy volunteers or patients, how the drug is 

studied and used (e.g., administered under continuous monitoring), as well as nonclinical data. 

1. Subject Enrollment (2.1.1) 

Subject enrollment for a given trial would be influenced by the clinical and nonclinical 

information available on the effects of the drug on cardiac repolarization. Until the effects of the 

drug on the QT/QTc interval have been characterized, the following exclusion criteria are 

suggested: 

• A marked baseline prolongation of QT/QTc interval (e.g., repeated demonstration of a 

QTc interval >450 milliseconds (ms)) 

• A history of additional risk factors for TdP (e.g., heart failure, hypokalemia, family 

history of Long QT Syndrome) 

• The use of concomitant medications that prolong the QT/QTc interval 

If supported by the QT/QTc interval data from the early clinical studies, later clinical trials could 

expand the eligibility criteria to include a broader spectrum of patients who are likely to receive 

the drug once approved. 

2. Safety Monitoring and Discontinuation Criteria (2.1.2) 

The clinical trial protocol should specify the procedures to follow if a patient experiences an 

adverse event suggestive of TdP. 

Discontinuation of a subject from a clinical trial should be considered if there is a marked 

prolongation of the QT/QTc interval during treatment with the study drug, especially if the 

measurement is obtained from more than one ECG. While increases in QT/QTc to >500 ms or 

of >60 ms over baseline are commonly used as thresholds for potential discontinuation, the exact 

criteria chosen for a given trial will depend on the risk-tolerance level considered appropriate for 

the indication and patient group in question. 

B. The “Thorough QT/QTc Study” (2.2 ) 

The “thorough QT/QTc study” is intended to determine whether the drug has a threshold 

pharmacologic effect on cardiac repolarization, as detected by QT/QTc prolongation. The 

threshold level of regulatory concern, discussed further below, is around 5 ms as evidenced by an 

upper bound of the 95% confidence interval around the mean effect on QTc of 10 ms. The study 

is typically carried out in healthy volunteers (as opposed to individuals at increased risk of 
Contains Nonbinding Recommendations

4

arrhythmias) and is used to determine whether or not the effect of a drug on the QT/QTc interval 

in target patient populations should be studied intensively during later stages of drug 

development. It is not intended to identify drugs as being pro-arrhythmic. Although data are 

limited, it is not expected that the results of the “thorough QT/QTc study” would be affected by 

ethnic factors. 

The “thorough QT/QTc study” would typically be conducted early in clinical development to 

provide maximum guidance for later trials, although the precise timing will depend on the 

specifics of the drug under development. It would usually not be the first study, as it is important 

to have basic clinical data for its design and conduct, including tolerability and 

pharmacokinetics. Some drugs might not be suitable for study in healthy volunteers because of 

issues related to tolerability (e.g., neuroleptic agents, chemotherapeutics). 

The results of the “thorough QT/QTc study” will influence the amount of information collected 

in later stages of development: 

• A negative “thorough QT/QTc study” will almost always allow the collection of ontherapy ECGs in accordance with the current practices in each therapeutic area to 

constitute sufficient evaluation during subsequent stages of drug development (see 

section II.C (2.3)). 

• A positive “thorough QT/QTc study” will almost always call for an expanded ECG 

safety evaluation during later stages of drug development (see section II.C (2.3)). 

There could be very unusual cases in which the “thorough QT/QTc study” is negative but the 

available nonclinical data are strongly positive (e.g., hERG (human ether-a-go-go-related gene) 

positive at low concentrations and in vivo animal model results that are strongly positive). If this 

discrepancy cannot be explained by other data, and the drug is in a class of pharmacological 

concern, expanded ECG safety evaluation during later stages of drug development might be 

appropriate (section 2.3). 

1. Design of the “Thorough QT/QTc Study” (2.2.1) 

The “thorough QT/QTc study” should be adequate and well-controlled, with mechanisms to deal 

with potential bias, including use of randomization, appropriate blinding, and concurrent placebo 

control group. As this study has a critical role in determining the intensity of ECG data 

collection during later stages of drug development, it is important to have a high degree of 

confidence in the ability of the study to detect differences of clinical significance. The 

confidence in the ability of the study to detect QT/QTc prolongation can be greatly enhanced by 

the use of a concurrent positive control group (pharmacological or nonpharmacological) to 

establish assay sensitivity. The positive control should have an effect on the mean QT/QTc 

interval of about 5 ms (i.e., an effect that is close to the QT/QTc effect that represents the 

threshold of regulatory concern, around 5 ms). Detecting the positive control’s effect will 

establish the ability of the study to detect such an effect of the study drug. Absence of a positive 

control should be justified and alternative methods to establish assay sensitivity provided. 
Contains Nonbinding Recommendations

5

If an investigational drug belongs to a chemical or pharmacological class that has been 

associated with QT/QTc prolongation, a positive control selected from other members of the 

same class should be considered to permit a comparison of effect sizes, preferably at equipotent 

therapeutic doses. 

Crossover or parallel group study designs can be suitable for trials assessing the potential of a 

drug to cause QT/QTc interval prolongation. Crossover studies at least have two potential 

advantages: 

• They usually call for smaller numbers of subjects than parallel group studies, as the 

subjects serve as their own controls and hence reduce variability of differences related 

to inter-subject variability. 

• They might facilitate heart rate correction approaches based on individual subject 

data. 

Parallel group studies might be preferred under certain circumstances: 

• For drugs with long elimination half-lives for which lengthy time intervals would be 

required to achieve steady-state or complete washout 

• If carryover effects are prominent for other reasons, such as irreversible receptor 

binding or long-lived active metabolites 

• If multiple doses or treatment groups are to be compared 

An important problem in the measurement of the QT/QTc interval is its intrinsic variability. 

This variability results from many factors, including activity level, postural changes, circadian 

patterns, and food ingestion. It is critical to address intrinsic variability in the conduct of the 

“thorough QT/QTc study.” This can be accomplished in several ways, including the collection 

of multiple ECGs at baseline and during the study. 

2. Dose-Effect and Time Course Relationships in the “Thorough QT/QTc Study” 

(2.2.2) 

An adequate drug development program should ensure that the dose-response and generally the 

concentration-response relationship for QT/QTc prolongation have been characterized, including 

exploration of concentrations that are higher than those achieved following the anticipated 

therapeutic doses. Data on the drug concentrations around the time of ECG assessment would 

aid this assessment. If not precluded by considerations of safety or tolerability due to adverse 

effects, the drug should be tested at substantial multiples of the anticipated maximum therapeutic 

exposure. Alternatively, if the concentrations of a drug can be increased by drug-drug or drugfood interactions involving metabolizing enzymes (e.g., CYP3A4, CYP2D6) or transporters 

(e.g., P-glycoprotein), these effects could be studied under conditions of maximum inhibition. 

This approach calls for an understanding of the pharmacokinetic and pharmacodynamic 

properties of the parent and significant human metabolites. In general, the duration of dosing or 

dosing regimen should be sufficient to characterize the effects of the drug and its active 

metabolites at relevant concentrations. 
Contains Nonbinding Recommendations

6

 3. Timing of ECGs in the “Thorough QT/QTc Study” (2.2.3) 

The timing of the collection of ECGs and the study design (e.g., single or multiple dose, 

duration) of the “thorough QT/QTc study” should be guided by the available information about 

the pharmacokinetic profile of the drug. For drugs with short half-lives and no metabolites, a 

single dose study might be sufficient. Studies should characterize the effect of a drug on the 

QT/QTc throughout the dosing interval. While the peak serum concentration does not always 

correspond to the peak effect on QT/QTc interval, care should be taken to perform ECG 

recordings at time points around the Cmax. As one intent of a positive control is to establish 

assay sensitivity, in multiple dose studies of new drugs a positive control needs to be used only 

long enough to have its expected effect. 

 4. Interpretation of the “Thorough QT/QTc Study” (2.2.4) 

It is difficult to determine whether there is an effect on the mean QT/QTc interval that is so small 

as to be of no consequence. However, drugs that prolong the mean QT/QTc interval by around 5 

ms or less do not appear to cause TdP. On that basis, the positive control (whether 

pharmacological or nonpharmacological) should be well-characterized and consistently produce 

an effect on the QT/QTc interval that is around the threshold of regulatory concern ( 5 ms, 

section 2.2). 

Based on similar considerations, a negative “thorough QT/QTc study” is one in which the upper 

bound of the 95% one-sided confidence interval for the largest time-matched mean effect of the 

drug on the QTc interval excludes 10 ms. This definition is chosen to provide reasonable 

assurance that the mean effect of the study drug on the QT/QTc interval is not greater than 

around 5 ms. When the largest time-matched difference exceeds the threshold, the study is 

termed ‘positive.’ A positive study influences the evaluations carried out during later stages of 

drug development, but does not imply that the drug is pro-arrhythmic. 

As with other data, the presence of outliers (see section III.B.2 (3.2.2)) should also be explored. 

5. Alternative Strategies to Assess QT/QTc Interval Effects (2.2.5) 

Alternatives to the use of the “thorough QT/QTc study” are under active investigation. 

Examples include evaluating the relationship between concentration and QT/QTc effects or more 

intensively evaluating ECGs, based on data collected during early phase clinical studies. 

C. Clinical Trial Evaluation After the “Thorough QT/QTc Study” (2.3) 

If the “thorough QT/QTc study” is negative (see section II.B (2.2)), the collection of baseline and 

periodic on-therapy ECGs in accordance with the current investigational practices in each 

therapeutic field is almost always sufficient evaluation during subsequent stages of drug 

development. 
Contains Nonbinding Recommendations

7

If the “thorough QT/QTc study” is positive, additional evaluation in subsequent clinical studies 

should be performed. One objective of this evaluation should be to fully describe the effect of 

the drug on the QT/QTc interval in the target patient population with particular attention to doseand concentration-related effects. It is important to include patients in these analyses exposed to 

the full range of potential doses and patients with additional risk factors for TdP. These analyses 

would ordinarily focus on outliers as well as on changes in mean QT/QTc. Depending on the 

size of the effect seen in the “thorough QT/QTc study, more intense monitoring of patients with 

additional risk factors for TdP might be needed. 

While what constitutes adequate ECG assessment to accomplish this is not fully established, 

additional ECGs collected appropriately in substantial numbers of patients in late phase clinical 

trials could provide this information. In this case, it would be important to collect ECGs at the 

anticipated time of peak drug effects, as determined in the “thorough QT/QTc study” and 

pharmacokinetic information about the patient population. 

Another objective of this evaluation should be to collect information on the adverse events that 

occur in the trials following the positive “thorough QT/QTc study.” This would include patients 

who develop marked QT/QTc prolongation (e.g., >500 ms) or experience a serious 

cardiovascular adverse event that suggests an arrhythmia (e.g., TdP). Such patients should be 

evaluated closely for risk factors that might have contributed to this event (e.g., genotyping for 

Long QT Syndromes, see section IV.C (4.3)). 

If the “thorough QT/QTc study” is positive, analyses of the ECG and adverse event data from 

certain patient sub-groups are of particular interest, such as: 

• Patients with electrolyte abnormalities (e.g., hypokalemia) 

• Patients with congestive heart failure 

• Patients with impaired drug metabolizing capacity or clearance (e.g., renal or hepatic 

impairment, drug interactions) 

• Female patients 

• Patients aged <16 and over 65 years 

Even if the “thorough QT/QTc study” is negative, if other evidence of an effect in a patient 

population from subsequent studies (e.g., marked QT/QTc interval prolongation, TdP) were to 

emerge, then additional investigation would be needed. 

D. Clinical Development When the “Thorough QT/QTc Study” Cannot Be 

Performed in Healthy Volunteers (2.4) 

There are some drugs that cannot be studied in a “thorough QT/QTc study” in healthy volunteers 

due to safety or tolerability concerns (e.g., cytotoxic cancer drugs). In such cases, the “thorough 

QT/QTc study” can often be conducted in patient populations. When this is not possible, the 

importance of detecting and modifying this safety risk means that other ways of detecting effects 

on the QT/QTc interval need to be developed. These might include the collection of ECGs at 

multiple time points under tightly controlled settings that target a broad range of doses early in 

development. 
Contains Nonbinding Recommendations

8

E. Collection, Assessment, and Submission of Electrocardiographic Data (2.5) 

The recommendations below are most relevant to the “thorough QT/QTc study” and to any 

studies investigating a drug with a known effect on cardiac repolarization and when the 

“thorough QT/QTc study” cannot be performed. 

1. Collection and Assessment of Standard 12-Lead ECGs (2.5.1) 

The clinical ECG database is typically derived from the collection of 12-lead surface ECGs, 

although ambulatory ECG techniques show promise (see section II.E.2 (2.5.2)). The quality of 

the ECG database can depend on the use of modern equipment with the capacity for digital 

signal processing. Such equipment should be recently serviced and calibrated. Machine 

calibration records and performance data should be maintained on file. In the case of multicenter 

trials, training sessions are encouraged to ensure consistency of operator technique (e.g., skin 

preparation, lead placement, patient position) and data acquisition practices. 

Several methods for measuring ECG intervals have been used in clinical trials, and for a given 

trial, the sponsor should describe the accuracy and precision of QT/QTc interval measurements 

using the selected system. The method chosen will depend on the level of precision appropriate 

for a given trial. For example, the “thorough QT/QTc study” would warrant particularly careful 

attention to interval measurement. At present, this would usually involve the measurement by a 

few skilled readers (whether or not assisted by computer) operating from a centralized ECG 

laboratory. If well-characterized data validating the use of fully-automated technologies become 

available, the recommendations in the guidance for the measurement of ECG intervals could be 

modified. Readers of ECGs should be blinded to time, treatment and subject identifier, and one 

reader should read all the ECG recordings from a given subject. The degree of inter- and intrareader variability should be established by having the assessors reread a subset of the data (both 

normal and abnormal) under blinded conditions. 

In the absence of a concern in the early clinical trial(s), ECG reading by machine has a role in the 

rapid assessment of ECGs for safety. Criteria for ECG diagnoses and for identification of 

adverse events should be pre-defined by the sponsor. 

While the most appropriate lead(s) and methodology to measure the QT interval have not been 

established, pre-cordial leads and lead II are often used. A consistent approach should be used 

for a given trial. 

Morphological changes in the T-U complex might occur. Information should be provided on 

changes in T and U wave morphologies (see section III.C (3.3)). 

Discrete U waves should be excluded from the QT/QTc interval measurement. 

 
Contains Nonbinding Recommendations

9

2. Ambulatory ECG Monitoring (2.5.2) 

While ambulatory ECG monitoring has historically not been considered sufficiently validated to 

be used as the primary assessment of QT/QTc interval, newer systems that allow for the 

collection of multiple leads that more closely approximate a surface ECG have potential value to 

collect interval data. The use of ambulatory ECG monitors might additionally allow detection of 

extreme QT/QTc interval events that occur infrequently during the day and asymptomatic 

arrhythmias. Data on the QT/RR from ambulatory ECG monitoring can also prove useful in the 

calculation of individualized QT corrections. However, as QT/QTc intervals measured by this 

methodology might not correspond quantitatively to those from standard surface ECGs, data 

obtained from the two methodologies might not be suitable for direct comparison, pooling, or 

interpretation using the same thresholds of concern. 

3. Submission of Interval and Waveform Data (2.5.3) 

Regional guidance should be sought for information on the submission of ECG interval data and 

overall assessments. 

III. ANALYSIS OF ECG DATA FROM CLINICAL TRIALS (3) 

Evaluation of the effects of a drug on the standard ECG intervals and waveforms is considered a 

fundamental component of the safety database of any new drug application. 

Regardless of the outcome of the “thorough QT/QTc study,” ECG changes recorded as adverse 

events should be pooled from all studies for analysis. ECG interval data from the “thorough 

QT/QTc study” should only be pooled with subsequent trials of similar rigor with regard to ECG 

data collection and analysis, but should not be pooled with trials using less rigorous ECG 

collection. Standardization of ECG collection for similar studies within a clinical trial program 

will facilitate pooled analyses. 

A. QT Interval Correction Formulae (3.1) 

As the QT interval has an inverse relationship to heart rate, the measured QT intervals are 

generally corrected for heart rate in order to determine whether they are prolonged relative to 

baseline. Various correction formulae have been suggested, of which Bazett’s and Fridericia’s 

corrections are the most widely used. In early trials evaluating the effects of a new drug on the 

QT/QTc interval in healthy volunteers, designed to detect relatively small effects (e.g., 5 ms), it 

is important to apply the most accurate correction available. 

Because the best correction approach is a subject of controversy, uncorrected QT and RR 

interval data, heart rate data, as well as QT interval data corrected using Bazett’s and Fridericia’s 

corrections should be submitted in all applications, in addition to QT interval data corrected 

using any other formulae. A concurrent positive control group is strongly encouraged to support 

the use of newer correction approaches (e.g., individual subject correction) in order to 

demonstrate the ability of the correction method to allow detection of relevant effects on the 

QT/QTc interval. 
Contains Nonbinding Recommendations

10

1. Population-Derived Correction Formulae (3.1.1) 

Examples of such corrections include the following: 

(1) Fridericia’s correction: QTc = QT/RR0.33

(2) Bazett’s correction: QTc =QT/RR0.5

Bazett’s correction is frequently used in clinical practice and in the medical literature. In 

general, however, Bazett’s correction overcorrects at elevated heart rates and under corrects at 

heart rates below 60 beats per minute (bpm) and hence is not an ideal correction. Fridericia’s 

correction is more accurate than Bazett’s correction in subjects with such altered heart rates. 

(3) Corrections based on linear regression techniques 

Application of linear regression techniques to plots of QT/RR data for the placebo or baseline 

study population allows for the estimation of the slope (b), which can be used for standardizing 

the data from both the drug and control groups to a normalized heart rate of 60 bpm, using the 

equation QT = a + b(1-RR). The Framingham correction [QTc = QT + 0.154(1-RR)] is one 

example of a correction derived by linear regression. 

(4) Corrections using linear or nonlinear regression modeling on pooled data from large 

databases 

2. Correction Formulae Derived from Within-Subject Data (3.1.2) 

Corrections for heart rate using individual subject data have been developed, applying regression 

analysis techniques to individual pre-therapy QT and RR interval data over a range of heart rates, 

then applying this correction to on-treatment QT values. These approaches are considered most 

suitable for the “thorough QT/QTc study” and early clinical studies, where it is possible to obtain 

many QT interval measurements for each study subject over a broad range of heart rates. As 

adaptation of the QT/QTc interval to changes in heart rate is not instantaneous, care should be 

taken to exclude ECG recordings collected during times of rapid heart rate changes due to this 

QT/RR hysteresis effect. 

 

B. Analysis of QT/QTc Interval Data (3.2) 

Although increases from baseline in the QT/QTc interval constitute signals of interest, 

interpretation of these differences is complicated by the potential for changes not related to 

drug therapy, including regression toward the mean and choice of extreme values. Regression 

toward the mean refers to the tendency of subjects with high baseline values to have lower 

values at later time points, while subjects with low baseline values tend to experience increases. 

The direction of regression depends on initial selection criteria (for example, if subjects with 

high baseline QT/QTc interval values are excluded from the trial, values recorded during 

treatment will tend to rise relative to baseline levels). The process of choosing the highest of 
Contains Nonbinding Recommendations

11

multiple observed values will also almost invariably cause an apparent change from any single 

baseline value, a phenomenon found in both drug and placebo-treated groups. 

The QT/QTc interval data should be presented both as analyses of central tendency (e.g., means, 

medians) and categorical analyses. Both can provide relevant information on clinical risk 

assessment. 

1. Analyses of Central Tendency (3.2.1) 

The effect of an investigational drug on the QT/QTc interval is most commonly analyzed using 

the largest time-matched mean difference between the drug and placebo (baseline-adjusted) over 

the collection period. Additional approaches to the assessment of central tendency could include 

analysis of changes occurring around the Cmax for each individual. This last analysis would be 

especially important if the drug has large between-subject variability in the rate of absorption or 

metabolism. 

2. Categorical Analyses (3.2.2) 

Categorical analyses of QT/QTc interval data are based on the number and percentage of 

patients meeting or exceeding some predefined upper limit value. Clinically noteworthy 

QT/QTc interval changes might be defined in terms of absolute QT/QTc intervals or changes 

from baseline. Separate analyses should be provided for patients with normal and elevated 

baseline QT/QTc intervals. As with all QT/QTc interval analyses, categorical analyses are 

most informative when it is possible to compare the rate of supra-threshold readings in the 

treatment and control groups. 

There is no consensus concerning the choice of upper limit values for absolute QT/QTc interval 

and changes from baseline. While lower limits increase the false-positive rate, higher limits 

increase the risk of failing to detect a signal of concern. In clinical trials, a prolongation of QTc 

> 500 ms during therapy has been a threshold of particular concern. Multiple analyses using 

different limits are a reasonable approach to this uncertainty, including: 

• Absolute QTc interval prolongation: 

- QTc interval > 450 

- QTc interval > 480 

- QTc interval > 500 

• Change from baseline in QTc interval: 

- QTc interval increases from baseline >30 

- QTc interval increases from baseline >60 
Contains Nonbinding Recommendations

12

3. Analysis of Relationship Between Drug Exposure and QT/QTc Interval Changes 

(3.2.3) 

Establishing the relationship of drug concentrations to changes in QT/QTc interval may provide 

additional information to assist the planning and interpretation of studies assessing cardiac 

repolarization. This area is under active investigation. 

C. Morphological Analyses of ECG Waveforms (3.3) 

While the predictive value of changes in ECG morphology, such as the development of U waves, 

has not been established, morphological abnormalities should be described and the data 

presented in terms of the number and percentage of subjects in each treatment group having 

changes from baseline that represent the appearance or worsening of the morphological 

abnormality. Typically these data will be obtained as a part of the “thorough QT/QTc study.” 

IV. ADVERSE EVENTS (4) 

In addition to data on changes in ECG intervals, adverse event data can be another source of 

information on proarrhythmic potential, including: 

• Premature discontinuations and dosage adjustments during clinical studies 

• Postmarketing adverse event reports if available 

A. Clinical Trial Adverse Events (4.1) 

Although drug-induced prolongation of the QT/QTc interval is usually asymptomatic, an 

increased rate of certain adverse events in patients taking an investigational agent can signal 

potential proarrhythmic effects. The rates of the following clinical events should be compared in 

the treated and control patients, particularly when there is evidence of an effect on the QT/QTc 

interval: 

• Torsade de pointes 

• Sudden death 

• Ventricular tachycardia 

• Ventricular fibrillation and flutter 

• Syncope 

• Seizures 

Torsade de pointes is very infrequently captured in clinical databases, even those for drugs 

known to have significant proarrhythmic effects. Given this, the failure to observe an episode of 

TdP in a drug application database is not considered sufficient grounds for dismissing the 

possible arrhythmogenic risks of a drug when these are suspected on the basis of ECG and other 

clinical data. The other adverse events listed above, while less specific for an effect on cardiac 

repolarization, are more commonly captured in clinical trials, and an imbalance in their 

frequency between study groups can signal a potential proarrhythmic effect of the investigational 

agent. Sub-group analyses should be conducted in terms of age, gender, pre-existing cardiac 

disease, electrolyte disturbances, and concomitant medications. Comparing cause-specific rates 
Contains Nonbinding Recommendations

13

of death is difficult, but a difference in the fraction of total deaths qualifying as “sudden” has 

also been proposed as a marker for proarrhythmic potential. 

Detailed patient narratives should be provided for all serious cardiac adverse events, as would be 

the case for any serious event or events leading to discontinuation. In assessing the possible 

causal relationship of drug-induced QT/QTc interval prolongation to the event, attention should 

be directed to considerations such as temporal relationship and ECG results collected at the time 

of the event. As the QT/QTc interval is subject to considerable fluctuation, a possible role for 

QT/QTc interval prolongation should not be dismissed on the basis of normal on-therapy ECG 

measurements performed prior to, or near the time of the adverse event. In addition to an 

appropriate adverse reaction report, patients with marked QT/QTc prolongation or an episode of 

TdP might provide useful information on risk management. When identified, they should 

therefore be examined closely for other risk factors (e.g., genetic predisposition, see section IV.C 

(4.3)). Rechallenge with the investigational drug under appropriately monitored conditions can 

provide useful information on dose- and concentration-response relationships. 

In evaluating the safety database of a new drug, consideration should be given to the extent to 

which the inclusion and exclusion criteria for patient eligibility might have influenced the study 

population with respect to the risk of QT/QTc interval prolongation and associated adverse 

events (e.g., exclusion of patients with cardiac co-morbidities or renal/hepatic impairment, 

prohibition of diuretics as concomitant medications). Ideally, the major clinical studies should 

include an adequate representation of female and elderly patients, as well as patients with comorbidities and concomitant medications typical of the expected user population. 

If a subject experiences symptoms or ECG findings suggestive of an arrhythmia during a clinical 

trial, immediate evaluation by a cardiac specialist is recommended, both for the purposes of 

treating the patient and for discussions related to continuation/ re-institution of the therapy. 

B. Premature Discontinuations or Dosage Reductions (4.2) 

Particular attention should be directed to subjects or patients who are discontinued from clinical 

trials due to QT/QTc interval prolongation. Information should be provided on the basis for 

premature discontinuation of the patient (e.g., a QT/QTc interval value in excess of a protocoldefined upper limit, occurrence of QT/QTc interval prolongation in association with symptoms 

of arrhythmia), as well as the dose and duration of treatment, plasma levels if available, 

demographic characteristics, and the presence or absence of risk factors for arrhythmia. 

 

Dosage reductions prompted by QT/QTc interval prolongation should also be documented. 

C. Pharmacogenetic Considerations (4.3)

Many forms of Long QT Syndrome are now known to be linked to mutations in genes encoding 

cardiac ion channel proteins. Because of incomplete penetrance, not all carriers of mutated ion 

channel genes will manifest QT/QTc interval prolongation in screening ECG evaluations. 

Polymorphisms can affect ion channels, leading to an increased sensitivity to drugs that affect 
Contains Nonbinding Recommendations

14

repolarization. Genotyping patients who experience marked prolongation of the QT/QTc or TdP 

while on drug therapy should be considered. 

D. Postmarketing Adverse Event Reports (4.4) 

Because documented cases of TdP are relatively rare, even for drugs that prolong the QT/QTc, 

they are often not reported until large populations of patients have received the agent in 

postmarketing settings. The available postmarketing adverse event data should be examined for 

evidence of QT/QTc interval prolongation and TdP and for adverse events possibly related to 

QT/QTc interval prolongation, such as cardiac arrest, sudden cardiac death and ventricular 

arrhythmias (e.g., ventricular tachycardia and ventricular fibrillation). A well-characterized 

episode of TdP has a high probability of being related to drug use, whereas the other events that 

are reported more commonly would be of particular concern if reported in a population at low 

risk for them (e.g., young men experiencing sudden death). 

V. REGULATORY IMPLICATIONS, LABELING, AND RISK MANAGEMENT 

STRATEGIES (5) 

A. Relevance of QT/QTc Interval Prolonging Effects 

 to the Evaluation Process (5.1) 

Substantial prolongation of the QT/QTc interval, with or without documented arrhythmias, could 

be the basis for nonapproval of a drug or discontinuation of its clinical development, particularly 

when the drug has no clear advantage over available therapy and available therapy appears to 

meet the needs of most patients. Failure to perform an adequate clinical assessment of the 

potential QT/QTc interval prolonging properties of a drug can likewise be justification to delay 

or deny marketing authorization. For non-antiarrhythmic drugs, the outcome of the risk benefit 

assessment will generally be influenced by the size of the QT/QTc interval prolongation effect, 

whether the effect occurs in most patients or only in certain defined outliers, the overall benefit 

of the drug, and the utility and feasibility of risk management options. The inclusion of 

precautionary material in the prescribing information will not necessarily be considered an 

adequate risk management strategy, if implementation of the recommendations in a clinical use 

setting is judged to be unlikely. 

If QT/QTc interval prolongation is a feature shared by other drugs of the therapeutic class in 

question, evaluation of the new drug could usefully involve a comparison of the magnitude and 

incidence of any QT/QTc interval prolongation effects relative to those of other members of its 

class in concurrent positive control groups. 

It is difficult to determine whether there is an effect on the mean QT/QTc interval that is so small 

as to be inconsequential, but the risk of arrhythmias appears to increase with the extent of 

QT/QTc prolongation. Drugs that prolong the mean QT/QTc interval by around 5 ms or less do 

not appear to cause TdP. Whether this signifies that no increased risk exists for these 

compounds or simply that the increased risk has been too small to detect is not clear. The data 

on drugs that prolong the mean QT/QTc interval by more than around 5 and less than 20 ms are 

inconclusive, but some of these compounds have been associated with proarrhythmic risk. Drugs 
Contains Nonbinding Recommendations

15

that prolong the mean QT/QTc interval by >20 ms have a substantially increased likelihood of 

being proarrhythmic, and might have clinical arrhythmic events captured during drug 

development. 

Regardless of the degree to which a drug prolongs the QT/QTc interval, decisions about its 

development and approval will depend upon the morbidity and mortality associated with the 

untreated disease or disorder and the demonstrated clinical benefits of the drug, especially as 

they compare with available therapeutic modalities. Demonstrated benefits of the drug in 

resistant populations or in patients who are intolerant of, or have a labeled contraindication to, 

approved drugs for the same disease represent additional relevant clinical considerations that 

might justify approval of the drug, if the indication were limited to use in such patients. 

Some factors have been proposed that can modify the risk of QT/QTc prolongation. For 

instance, it has been suggested that some drugs might prolong the QT/QTc interval up to a 

“plateau” value, above which there is no dose-dependent increase, although this has not been 

demonstrated adequately to date. It has also been suggested that proarrhythmic risk might be 

influenced by other pharmacologic effects (e.g., other channel effects). In any case, it is 

important to identify the “worst case scenario” for drugs that have demonstrated effects on 

QT/QTc interval as a part of risk assessment (i.e., the QT/QTc interval measured in the target 

patient population at the time of peak effect and under conditions of the highest blood levels that 

can be attained during therapy). 

B. Labeling Issues for Drugs that Prolong the QT/QTc Interval (5.2) 

It is recognized that there will be regional differences in labeling. However, it is recommended 

that the following be considered: 

• A warning/precautionary statement about the risk 

• A description of the design and results of the trials investigating the effect on the 

QT/QTc interval, including the absence of demonstrated effect 

• The dosage recommendations 

• A list of conditions known to increase the proarrhythmic risk (e.g., congestive heart 

failure, Long QT Syndrome, hypokalemia) 

• A precautionary statement regarding the concomitant use of two or more QT/QTc 

interval prolonging drugs and other interactions increasing the risk 

• Recommendations for patient monitoring (ECG and electrolytes) and management of 

patients with QT/QTc prolongation or symptoms suggestive of an arrhythmia 

C. Postmarketing Risk Management for Drugs that Prolong the QT/QTc 

Interval (5.3) 

The use of dosing adjustments following institution of therapy appears to materially decrease the 

risk of TdP in hospitalized patients receiving an antiarrhythmic drug; no similar data are 

available for drugs of other therapeutic classes. For approved drugs that prolong the QT/QTc 
Contains Nonbinding Recommendations

16

interval, risk-management strategies aimed at minimizing the occurrence of arrhythmias 

associated with their use have focused on education of the health care providers and patients.