Risk Stratification of Sudden Cardiac Death After Acute Myocardial Infarction

Abstract

Despite advances in the diagnosis and treatment of acute coronary syndromes and an overall improvement in outcomes, mortality after myocardial infarction (MI) remains high. Sudden death, which is most frequently due to ventricular tachycardia or ventricular fibrillation, is the cause of death in 25% to 50% of patients with prior MI, and therefore represents an important public health problem. Use of the implantable cardioverter-defibrillator (ICD), which is the primary method of reducing the chance of arrhythmic sudden death after MI, is costly to the medical system and is associated with procedural and long-term risks. Additionally, assessment of left ventricular ejection fraction (LVEF), which is the primary method of assessing a patient's post-MI sudden death risk and appropriateness for ICD implantation, lacks both sensitivity and specificity for sudden death, and may not be the optimal way to select the subgroup of post-MI patients who are most likely to benefit from ICD implantation. To optimally utilize ICDs, it is therefore critical to develop and prospectively validate sudden death risk stratification methods beyond measuring LVEF. A variety of tests that assess left ventricular systolic function/morphology, potential triggers for ventricular arrhythmias, ventricular conduction/repolarization, and autonomic tone have been proposed as sudden death risk stratification tools. Multivariable models have also been developed to assess the competing risks of arrhythmic and non-arrhythmic death so that ICDs can be utilized more effectively. This manuscript will review the epidemiology of sudden death after MI, and will discuss the current state of sudden death risk stratification in this population.

Keywords: Myocardial infarction; risk stratification; sudden cardiac death.

Figure 1:

The relative number of sudden deaths that were attributed to MI/myocardial rupture versus those attributed to presumed arrhythmia occurring at various time points after MI in patients in the VALIANT trial. The rate of non-arrhythmic sudden death is highest in the early post-MI period and then decreases over time. Adapted from Pouleur AC, Barkoudah E, Uno H, et al. Pathogenesis of sudden unexpected death in a clinical trial of patients with myocardial infarction and left ventricular dysfunction, heart failure, or both. Circulation. 2010;122(6):597–602.

Figure 2:

The relationship between risk score and two-year rates of total mortality and arrhythmic death/cardiac arrest in patients in the MUSTT trial. AD/CA: arrhythmic death/cardiac arrest; TM: total mortality. Reproduced with permission from Buxton AE, Lee KL, Hafley GE, et al. Limitations of ejection fraction for prediction of sudden death risk in patients with coronary artery disease. Lessons from the MUSTT study. J Am Coll Cardiol. 2007;50:1150–1157.

Figure 3:

Two-year mortality in patients with and without ICDs in the MADIT-II trial. No significant survival benefit associated with ICD implantation was seen in patients with no risk factors, or in those patients at very high risk due to the presence of severe renal dysfunction. *p < 0.05 for the comparison between conventional therapy (Conv.) and ICD groups. VHR: very high risk. See text for further details. Reproduced with permission from Goldenberg I, Vyas AK, Hall WJ, et al. Risk stratification for primary implantation of a cardioverter-defibrillator in patients with ischemic left ventricular dysfunction. J Am Coll Cardiol. 2007;51(3):288–296.