Continuous electrocardiographic monitoring for more than one hour does not improve the prognostic value of ventricular arrhythmias in survivors of first acute myocardial infarction

Validation of a short rhythm strip compared to ambulatory ECG monitoring for ventricular ectopy

Premature ventricular contractions (PVCs) are associated with an increased risk of cardiovascular disease and mortality. Many epidemiologic studies measure a continuous short rhythm strip to ascertain PVCs as a screening tool to identify persons at highest risk. Despite its widespread use in epidemiologic studies, the rhythm strip has not been completely validated. Therefore, a continuous 2-min rhythm strip was measured on 242 consecutive individuals referred for ambulatory ECG monitoring. Prevalence of at least one PVC on the 2-min rhythm strip was compared to a gold standard, the average number of PVCs per hr on ambulatory recording. The prevalence of any PVCs on the 2-min rhythm strip was 19%. As average PVCs per hr increased on the ambulatory ECG recording, sensitivity increased while specificity slowly decreased. Sensitivity ranged from 26-100% and specificity ranged from 81-100% across the distribution of average PVCs per hr on ambulatory monitoring. Area under the receiver operator characteristic (ROC) curve of the 2-min rhythm strip compared to 24-hr results was 0.943. Area under ROC curves were not statistically different (P > 0.05) by age, gender, hypertension status, or history of myocardial infarction. In this clinical population, utilizing the 2-min rhythm strip as an indicator of average PVCs per hr had excellent specificity and moderate to low sensitivity across most of the distribution of average PVCs per hr. The use of a short rhythm strip to detect PVCs may be considered useful in epidemiologic investigations of cardiovascular disease and mortality for detecting high frequency PVCs in populations. The use of a short rhythm strip as a screening tool to detect PVCs in clinical practice is not warranted, based on our findings and the existing literature. However, an awareness that PVCs on a 2-min rhythm strip consistently identify high frequency PVCs on 24-hr recordings should be helpful to clinicians.

[Predictors of sudden death in coronary artery disease]

Although advances in the management of acute myocardial infarction have resulted in a decline in long-term risk of sudden death, it continues to be high in certain subsets of patients. Thus, it is important to identify and treat these patients. Left ventricular ejection fraction less than 0.40, frequent premature ventricular ectopy on Holter monitoring, late potentials on signal-averaged electrocardiogram, impaired heart rate variability, abnormal baroreflex sensitivity and inducible sustained monomorphic ventricular tachycardia during electrophysiological study are predictors of sudden death and arrhythmic events. Although the negative predictive value of each factor is high, the positive predictive accuracy is low. Several tests can be combined to obtain higher positive predictive values. In fact, in some studies combined noninvasive tests have been used to select patients for ventricular stimulation study. Some preventive treatment can be applied in these patients. Available data do not justify prophylactic therapy with amiodarone in high-risk survivors of acute myocardial infarction. Sudden death and total mortality have been significantly reduced in postinfarction patients by long-term beta blockade. Hence, beta blockers should be given to all patients with acute myocardial infarction who do not have contraindications to their use. The MADIT study has shown the beneficial effect of implantable cardioverter defibrillator in reducing mortality in patients with prior myocardial infarction, an ejection fraction less than 0.36, asymptomatic nonsustained ventricular tachycardia, and inducible sustained ventricular tachycardia, unsuppressable by procainamide. Besides, several studies are under way to evaluate the prophylactic use of implantable defibrillator for improving survival in high-risk patients.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.