The Signal-averaged ElectrocArdiogram in Long Term Follow-up of Chronic CHagas Disease - RIO de Janeiro Cohort
Condition: Chagas Cardiomyopathy; Cardiac Arrhythmia; Stroke; Left Ventricular Function Systolic Dysfunction; Cardiac Death
MeSH terms: Chagas Cardiomyopathy; Cardiomyopathies; Arrhythmias, Cardiac; Death
Study type: Observational

Summary: 
      The study investigated 100 subjects, both genders, with chronic Chagas disease, confirmed by
      at least two distinct serological tests, and classified according to Los Andes classification
      in a long term follow-up aiming at identifying the predictive value of the signal-averaged
      electrocardiogram for cardiac death and ventricular tachycardia.

      All subjects admitted to the study were submitted to clinical history taking, physical
      examination, and noninvasive assessment, including blood pressure measurement, resting
      12-lead surface electrocardiogram, 24h ambulatory electrocardiogram monitoring,
      M-Mode/two-dimensional echocardiogram, signal-averaged electrocardiogram in both time and
      frequency domains. Selected subjects were further submitted to treadmill stress test and
      coronary angiography to rule out coronary heart disease.

      Subjects were followed by non-investigational primary care assistance at three to six months
      scheduled clinical visits on an outpatients basis. Both noninvasive and invasive evaluation
      during follow-up were requested at discretion of primary evaluation. Adverse outcomes were
      ascertained by review of medical records and active contact to either study subjects or their
      relatives.
    

Detailed description: 
      Admission:

      Longitudinal prospective study, with a cohort of 100 consecutive outpatient subjects (34 to
      74 years old; 31 females) with Chagas' disease followed-up for at least 10 years at the
      cardiomyopathy outpatient clinic of University Hospital, Rio de Janeiro, RJ, Brazil, a
      tertiary care center. Enrollment was from 1995 to 1999. Subjects were born in endemic regions
      of Minas Gerais, Goias or Bahia States of Brazil and Chagas' disease was diagnosed on basis
      of two positive serum tests, hemagglutination cruzipain-ELISA and indirect
      immunofluorescence. All subjects were referred to the arrhythmia for risk stratification. At
      the time of admission none had received nitroderivative therapy. Subjects were classified
      according to the severity of heart involvement according to Los Andes classification, and
      divided into three groups: class I - 28 subjects (group 1), class II - 48 subjects (group 2),
      and class III - 24 subjects (group 3). Clinical and laboratory data were assessed during a
      personal interview and review of medical records. On admission, all subjects were in New York
      Heart Association functional class I or II, had normal sinus rhythm and normal PR intervals.
      Exclusion criteria at initial enrollment were: any degree of atrioventricular block or
      non-sinus rhythm, previous documented acute coronary events (unstable angina or myocardial
      infarction), chronic obstructive pulmonary disease, rheumatic valvular heart disease, alcohol
      addiction, thyroid dysfunction or abnormal serum electrolytes. Treadmill stress test and/or
      coronary artery angiogram were indicated in selected subjects to rule out concomitant
      coronary artery disease. World Health Organization and Helsinki Treaty regulations reviewed
      in Venice (1983) were followed and all subjects provided informed consent to participate.

      Clinical follow-up:

      All subjects have been followed-up by the same team of physicians. Medical visits have been
      scheduled at the outpatient clinics in a three to six-month interval. Medications were
      prescribed at the discretion of the physician who performed the primary evaluation. Body
      weight varied <2 kg during follow-up, and serum potassium varied from 3.5 to 5
      milliequivalent/L. Mild systemic arterial hypertension (systolic arterial pressure ranging
      from 140 mmHg and 155 mmHg, or diastolic arterial pressure ranging from 90 mmHg and 105 mmHg)
      was observed in 41% of the subjects and all received anti-hypertensive medication (converting
      enzyme inhibitors, diuretics, vasodilators and/or beta-blockers) at the discretion of the
      physician who performed the primary evaluation in order to reduce blood pressure levels to
      less than 140/90 mmHg. All regularly followed at scheduled clinical visits. The endpoints
      were described elsewhere in this registry. All causes of adverse events were ascertained by
      active search of relatives and review of the medical records.

      Resting surface 12-lead ECG and plain chest roentgenogram

      For each patient, standard resting 12-lead ECGs were recorded in the supine position (with
      simultaneous 3-lead acquisition) with a Cardimax ECAPS 12 2000 Compliant Electrocardiograph
      (Nihon-Kohden Co, Tokyo, Japan). Electrocardiographic abnormalities were classified according
      to standard criteria for conduction disturbances (intraventricular and atrioventricular),
      chamber overload, and abnormal Q waves [11]. The electrocardiographic variables assessed is
      sinus rhythm were: maximum P-wave duration and PR interval (typically in lead II), QRS
      complex duration (the longest ventricular duration in precordial leads), maximal absolute QRS
      complex in any precordial lead, presence of bundle branch block and/or left fascicular-block,
      presence of abnormal Q waves (Q-wave, defined as the first QRS deflection >1-mm deep and
      >0.04-ms wide), and left atrial overload (P-wave duration in lead II >110 ms or Morris index
      in V1 >4 millivolt.ms). In antero-septal leads (V1, V2 and V3) and in inferior leads (L2, L3
      and aVF) the presence of Q-wave in two out of three leads was considered abnormal. An
      independent observer blind to the study analyzed the electrocardiographic records that were
      automatically obtained from electrocardiograph equipment. Subsequent 12-lead resting ECGs
      were recorded at each clinical visit in order to assess cardiac rhythm during follow-up.
      Plain chest roentgenogram was carried out on the same day and cardiomegaly was defined by a
      cardiothoracic ratio of more than 0.50.

      M-mode/2-D Echocardiogram

      M-mode and two-dimensional echocardiograms were performed using an Apogee CX-200 equipment
      (ATL, Bothell, Washington, USA) with a 4-megahertz broadband transducer. The echocardiograms
      were analyzed by a trained observer blinded to the study protocol Echocardiographic
      parameters were assessed according to standard procedures of the Section of Echocardiography
      of the Department of Cardiology, with special care taken to detect left ventricular apical
      aneurysms. The echocardiographic parameters assessed were left ventricular ejection fraction
      (LVEF) calculated by the teichholz method, left atrial diameter (LAD), presence of pulmonary
      arterial hypertension (defined as maximal pulmonary arterial pressure > 30 mmHg, diastolic
      dysfunction, and the presence of an apical aneurysm. Normal cut-off value for LVEF was
      defined as >50%. Routine echocardiograms were performed in order to track changes in LVEF
      during follow-up.

      24h Ambulatory ECG Monitoring

      Twenty-four-hour ambulatory ECG monitoring was performed using a three-channel
      DMS-cassette-tape recorder and carefully analyzed using the Del-Mar Avionics StrataScan
      System (Del Mar Avionics, Irvine, California, USA) by a trained observer blind to the study
      in order to assess the presence of ventricular arrhythmia and atrioventricular conduction
      disturbances. Variables assessed in the 24h ambulatory ECG were: i) isolated premature
      supraventricular contractions ii) nonsustained supraventricular tachycardia defined as a
      sequence of three of more supraventricular ectopic beats, iii) isolated premature ventricular
      contractions, and iv) ventricular tachycardia episodes (defined as: heart rate >100 bpm, QRS
      duration >120 ms, three or more consecutive ventricular complexes, and atrial-ventricular
      dissociation).

      The standard-deviation of all consecutive normal interbeat intervals in 24h (24h SDNN) was
      employed to assess heart rate variability. Normal cut-off point was defined at >=100ms.
      During follow-up, 24h ambulatory ECG were performed at the discretion of attending
      physician's judgment in order to assess cardiac rhythm and arrhythmia. One trained specialist
      blind to Los Andes classification groups analyzed all tape recordings immediately after their
      acquisition.

      Signal-averaged electrocardiogram

      Signal-averaged electrocardiogram (SAECG) was employed to asses the presence of both
      ventricular late potentials and intraventricular electrical transients (IVET).

      SAECG was acquired in sinus rhythm with a Predictor-IIc equipment (ART Inc., Fitchburg,
      Massachusetts, USA) using modified XYZ Frank orthogonal leads and QRS-triggered
      coherent-averaged up to the noise level of 0.3 microvolt. SAECGs were analyzed in both time
      and frequency domains by an independent observer blinded to the study patients information.
      After signal average ECG acquisition, time domain analysis was carried out on vector
      magnitude (VM), using a bidirectional 4th order 40 Hz to 250 Hz band-pass Butterworth filter.
      The variables extracted from VM were: duration of VM (DUR [ms]), root-mean-squared voltage of
      last 40ms of VM (RMS40[microvolt]) duration of potentials below 40 microvolt at the terminal
      portion of VM (LAS40[ms]). Due to the presence of bundle branch block as a common finding in
      Chagas disease, normal cut-off point for DUR was defined at >150ms.

      The onset and offset points of VM delimited the analytic region for frequency domain
      analysis, by using the spectral turbulence analysis approach. The analytic region in VM was
      preprocessed to extract the first derivative, aiming at removing the high-amplitude
      low-frequency components. The derived signal was cut into slices to build a power spectral
      density time-frequency map by applying the short-time Fourier transform. Each data segment
      was limited in 25 ms, with 2 ms interval between successive segments to assure adequate
      time-resolution, tapered by a Blackmann-Harris window after mean removal, and zero-padded to
      64 points. After Fourier transform of a particular segment, its spectral amplitude was
      squared to obtain the estimated power spectral density function. Successive power spectral
      density function estimates in the analytic region were attached in a three-dimensional map.
      The boundaries of the analytic region (up to 200 ms duration) were placed 25 ms prior to the
      onset of the VM and to a point on the ST segment 50 ms after the offset of the VM. In the
      time frequency map, spectral turbulence was studied by comparing sequential spectral
      estimates. We calculated Pearson's correlation coefficient between adjacent power spectral
      function estimates throughout ventricular activation, and deployed the correlation
      coefficients in a time series, of which the mean and the standard deviation of the
      intersegment spectral correlation (abbreviated as MSC and SSC, respectively) were calculated.
      Additionally, we calculated the frequency corresponding to 80% of the total area under a
      particular power spectral function estimate, starting at zero Hz, which practically
      represented the edge or the border, and deployed the edge frequency, thus calculated, in a
      time series. The mean and the standard deviation of the electrical transients (abbreviated as
      MET and SET, respectively) of the edge frequency series were extracted. Power spectral
      estimates were limited to the range from 0 to 300 Hz in order to avoid interference of high
      frequency noise during correlation. MSC and SSC were multiplied by 100 to simplify
      calculations. Normality threshold values have been defined previously as MSC>94, SSC<=6,
      MET<=78 and The SET<=31. The presence of intraventricular electrical transients (IVET+) was
      optimally defined when 2 out of 4 variables were outside normality range. We used the above
      method based on our hypothesis that the presence of high frequency electrical transients,
      representing underlying electrically unstable myocardial areas, would determine the reduction
      of intersegment correlation. Likewise, high frequency transients would increase the energy
      content of a spectral estimate and the shift the spectral border rightward, to a higher
      frequency.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        One hundred clinically stable subjects with at least 10 years of regular outpatients
        follow-up and positive epidemiological history and serological confirmation of Chagas
        disease with ate least two immunological tests.
      
Keywords: Chagas heart disease; ventricular tachycardia; atrial fibrillation; stroke; cardiac death; signal averaged electrocardiogram