Microvolt T Wave Alternans Testing for Risk Stratification of Post-Myocardial Infarction Patients - MASTER (Microvolt T-Wave)

Description:

The goal of the trial was to evaluate use of microvolt T-wave alternans (MTWA) testing for risk stratification of life-threatening ventricular tachyarrhythmic events among post-myocardial infarction (MI) patients with impaired ejection fraction undergoing implantable cardioverter defibrillator (ICD) implantation.

Hypothesis:

MTWA would predict ventricular tachyarrhythmias among patients with impaired ventricular function after MI.

Study Design

Patients Enrolled: 654
Mean Follow Up: 2 years
Mean Patient Age: 65 years
Female: 16

Patient Populations:

Prior MI with left ventricular ejection fraction ≤30% and met MADIT-II indication for ICD implantation

Exclusions:

Atrial fibrillation or flutter at time of MTWA testing; prior clinical sustained ventricular tachycardia/ventricular fibrillation; MI ≤1 month; revascularization ≤3 months; electrophysiology study or MTWA testing ≤1 year

Primary Endpoints:

Risk stratification for life-threatening ventricular tachyarrhythmic events

Secondary Endpoints:

Total mortality (sudden cardiac, nonsudden cardiac, noncardiac)

Drug/Procedures Used:

All patients underwent MTWA testing at baseline and were classified as MTWA negative or all others (positive or indeterminant). If testing was initially indeterminant, testing was to be repeated if possible. After testing, ICD implantation was then performed. Repeat MTWA testing was performed every 12 months.

Concomitant Medications:

At baseline, the use of aspirin was 78%, angiotensin-converting enzyme inhibitor or angiotensin-receptor blocker was 83%, beta-blocker was 87%, statin was 78%, and digoxin was 23%.

Principal Findings:

Baseline MTWA was negative in 37% of patients, positive in 51%, and indeterminate in 12%. Mean ejection fraction was 24%. A history of atrial fibrillation was present in 18% of the cohort. Cardiac resynchronization therapy was used in 23% of the population. Patients with a non-negative MTWA test were generally higher risk at baseline than patients with a negative MTWA, including being older (mean age 66 years for the non-negative group vs. 63 years for the negative group, p = 0.006), and more frequently having a QRS duration ≥120 msec (55% of the non-negative group vs. 44% of the negative group, p = 0.01).

The primary endpoint of life-threatening ventricular tachyarrhythmic events occurred in 10.3% of the MTWA-negative cohort and 13.3% of the non-negative cohort (hazard ratio [HR] 1.26, 95% confidence interval 0.76-2.09, p = 0.37). Results were similar when excluding the indeterminate MTWA group. Total mortality was lower in the MTWA-negative cohort compared with the non-negative cohort (6% vs. 13%, HR 2.04, p = 0.02), but among the causes of death, the difference in mortality was not driven by sudden death, but by noncardiac deaths.

Interpretation:

Among post-MI patients with impaired ejection fraction undergoing ICD implantation, risk stratification using MTWA testing was not associated with a difference in prediction of life-threatening ventricular tachyarrhythmic events.

According to the author, MTWA is thought to be a marker for electrophysiological abnormalities that predispose to re-entrant ventricular arrhythmias. A non-negative MTWA was associated with a higher risk of total mortality, but not specifically an increase in arrhythmic death. These findings suggest that a positive MTWA test may just identify a cohort of sicker patients, as evidenced by the increase in baseline risk and the increase in total mortality, but not identify a cohort at higher risk of sudden death. Similar results have been shown with other studies of MTWA testing. Predicting arrhythmic death has proven elusive, with limited clinical or physiologic parameters identified that correlate with sudden death.

References:

Chow T, Keriakes DJ, Onufer J, et al., on behalf of the MASTER Trial Investigators. Does Microvolt T-Wave Alternans Testing Predict Ventricular Tachyarrhythmias in Patients With Ischemic Cardiomyopathy and Prophylactic Defibrillators? The MASTER (Microvolt T Wave Alternans Testing for Risk Stratification of Post-Myocardial Infarction Patients) Trial. J Am Coll Cardiol 2008;52:1607-15.

Presented by Dr. Theodore Chow at the American Heart Association Annual Scientific Session, Orlando, FL, November 2007.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Implantable Devices, SCD/Ventricular Arrhythmias, Acute Heart Failure

Keywords: Myocardial Infarction, Ventricular Fibrillation, Death, Sudden, Glucans, Cardiac Resynchronization Therapy, Cause of Death, Tachycardia, Ventricular, Heart Failure, Ventricular Function, Stroke Volume, Confidence Intervals, Defibrillators, Implantable


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