Competency in Interpretation of 12-Lead Electrocardiograms: A Summary and Appraisal of Published Evidence

Interpretations of 12-lead resting electrocardiograms (ECGs) are often required in both ambulatory and inpatient settings. Organizations, including the American College of Cardiology (ACC) and the American Heart Association (AHA), have published consensus-based competency standards suggesting the optimal number of ECGs necessary to obtain and maintain competency in ECG interpretation skills. The ACC/AHA guidelines recommend interpreting a minimum of 500 supervised ECGs during initial training, using standardized testing in ECG interpretation to confirm initial competency and interpreting 100 ECGs yearly to maintain competency (1). The consensus statement asserts that these standards should apply to all practice settings and situations; however, the statement is controversial because of the lack of evidence-based literature on the optimal techniques for learning, maintaining, and testing competency in ECG interpretation. This systematic review attempts to synthesize the literature that may prove useful for physicians, program directors, and organizations seeking alternative evidence-based information on physician ECG interpretation skills. Methods We retrieved information through systematic searches and ongoing surveillance of MEDLINE (1996 to 2002), EMBASE (1974 to 2002), and the Cochrane Controlled trials Register (1975 to 2002). We used the following index terms and text words: electrocardiogram interpretation, electrocardiogram competency, electrocardiogram training, electrocardiogram errors, and computer electrocardiogram interpretation. Our search was limited to English-language articles that studied adult participants. References of the full-length articles were analyzed for additional citations. The search revealed 419 articles of potential interest. After we analyzed the abstracts of these articles, we eliminated 378 because ECG interpretation was not the main study focus. Thirty-nine articles and 2 letters to the editor contained research data directly related to ECG interpretation. We divided the articles into the following broad categories: studies that included clinical outcomes (Table 1), studies that included discussion of the accuracy of computer ECG interpretation (Table 2), and all other studies that compared noncardiologists to a cardiologist reference standard (Table 3). The studies were not graded by quality. Although criteria exist for grading the quality of studies of diagnostic tests, the focus of our study was the users of the test rather than the usefulness of electrocardiography for diagnosing specific diseases. We also reviewed the recommendations of the American Board of Internal Medicine, American College of Physicians, AHA, ACC, and Accreditation Council on Graduate Medical Education Residency Review Committees for Internal Medicine and Cardiovascular Diseases (1, 43-45). Table 1. Electrocardiogram Interpretation Studies with Clinical Outcomes Table 2. Electrocardiogram Interpretation Studies Comparing Computer and Physician Interpretation Table 3. Electrocardiogram Interpretation Studies without Outcomes Related to Interpretation Errors Reference Standards for Determining ECG Interpretation Accuracy One common feature of most ECG interpretation studies is the use of an expert electrocardiographer gold standard, typically a consensus panel of cardiologists. This may be problematic because interpretations by several cardiologists reading the same ECG often vary substantially (14, 17, 29, 42). Even one cardiologist reading the same ECG on separate occasions may have substantially different interpretations (14, 29, 42). Most studies on ECG interpretation by cardiologists report the proportion of abnormal diagnoses that are correctly identified, as determined by a consensus panel. These studies report that the participating cardiologists correctly determined 53% to 96% of the abnormalities identified by the reference standard (4, 17, 21, 23, 24, 28, 30). Two recent studies examined whether cardiologists agreed among themselves and their colleagues by using statistics to adjust for interpretations that agreed on the basis of chance alone (14, 29). Holmvang and colleagues reviewed 502 ECGs examined by both local cardiologists and an expert electrocardiography consensus panel (29). Agreement was poor to moderate on identification of ST-segment elevation ( = 0.05), ST-segment depression ( = 0.38), and a normal ECG ( = 0.42). Interrater agreement on detecting T-wave inversion was very good ( = 0.63). In contrast, intrarater agreement by the expert electrocardiographic consensus panel was good ( = 0.58 to 0.67). Levels of agreement may be higher for serious abnormalities, such as ST-segment elevation criteria for use of thrombolytic therapy. Massel and colleagues reported substantial agreement ( = 0.78) among three cardiologists examining whether 75 ECGs met criteria for thrombolytic therapy (14). The study also showed good intrarater agreement ( = 0.67 to 0.71) when the three cardiologists determined criteria for thrombolytic therapy on two separate occasions. Because cardiologists do not agree on many aspects of ECG interpretation, future studies examining noncardiologist or computer interpretation should include statistics and control groups of cardiologists. Readers can then draw more sophisticated conclusions about the importance of disagreements in ECG analysis. More accurate measures of agreement, such as weighted statistics, should be included because disagreement may relate to only some aspects of the ECG interpretation. Frequency of ECG Interpretation Errors by Staff and Resident Physicians Numerous trials have compared the ECG interpretation skills of cardiologists and noncardiologists. Most studies measured the proportion of ECG diagnoses determined by an expert consensus panel gold standard that noncardiologist physicians could identify. Seven studies measuring comprehensive ECG analysis found that the proportion of ECG diagnoses correctly identified by noncardiologist physicians ranged from 36% to 96% (4-6, 8, 11, 13, 33). In several studies that focused on a particular aspect of ECG interpretation, noncardiologists identified 87% to 100% of ECGs showing acute myocardial ischemia (6, 27), correctly classified 72% to 94% of ECGs as meeting inclusion criteria for thrombolytic therapy (3, 26, 30, 32, 37, 40), diagnosed 57% to 95% of ST-segment abnormalities (2, 9, 26), and correctly measured about 25% of PR and QT intervals (36). Although most studies combined resident and staff physicians in their analyses, some provided data allowing subgroup analysis. Twelve articles included information specifically on resident physician interpretation skills. Resident physicians detected 96% of abnormal ECGs (15), correctly identified inclusion criteria for thrombolytic therapy 73% to 84% of the time (3, 26, 30, 32), demonstrated 36% to 80% of ECG diagnoses as determined by expert electrocardiographers (5, 6, 11, 13, 21, 28, 41), and discovered 38% of technical ECG abnormalities (41). Only two articles provided sufficient information for subgroup analysis on noncardiologist staff physicians. The articles did not provide information on specialty background or board certification. Staff physicians correctly identified inclusion criteria for thrombolytic therapy 77% of the time (30) and diagnosed abnormal ST-segment and T-wave abnormalities 57% to 97% of the time (16). Four studies provided information on the ECG interpretation skills of nonphysicians. In two studies, nurses correctly identified ECG criteria for thrombolytic therapy 84% to 94% of the time (30, 37). The other studies examined the interpretation skills of medical students (28, 38), who identified 17% to 63% of ECG abnormalities identified by an expert reference standard. Trainees often gain experience in ECG interpretation when they use an ECG to assist in the clinical management of a patient. Not surprisingly, research has shown that clinical history may affect interpretation of ECGs (28, 31, 38). Providers with less training are influenced by the history to a greater extent than are more experienced electrocardiographers. For example, when given a misleading history, diagnostic accuracy was reduced by 5% for cardiologists but up to 25% for residents in one recent study (28). Cardiologists performed better than other interpreters in all settings and were 90% accurate in their diagnoses, even when no history was provided. Another study also demonstrated that interpretations by cardiologists were minimally dependent on the presence or absence of history (46). This information suggests that noncardiologist interpreters may make more accurate interpretations when they know the clinical context of the ECG. False-positive ECG interpretations could lead to unnecessary patient treatment. Six studies examined this aspect of interpretation (9, 15-17, 37, 40). Cardiologists typically had fewer false-positive interpretations than did noncardiologists. Cardiologists demonstrated a specificity of 93% to 100% for diagnosis of substantial ECG abnormalities, such as myocardial ischemia; specificity for noncardiologist physicians was 73% to 100%. In simpler determinations, such as differentiating normal from abnormal ECGs, the specificity of noncardiologists also approached that of cardiologists (15). Severity and Consequences of Errors in ECG Interpretation Eleven studies examined whether ECG interpretation errors could affect patient management, and seven measured patient outcomes (Table 1). Thirteen studies assessing the severity of interpretation errors reported that 4% to 33% of interpretations contained errors of major importance (2-13, 21). Expert consensus panels studied the charts of patients with ECG interpretation errors and determined whether a correct ECG interpretation would have changed patient management. This more detailed analysis revealed inappropriate management as a result of interpretation errors in 0% to 11% of cases (Tabl