Welcome to Touch Briefings

Yi Gang and Marek Malik
American Heart Journal Volume 7 No.1

---

Heart rate variability (HRV) is a beat-to-beat variation in cardiac cycle length resulting from autonomic influence on the sinus node of patients in sinus rhythm. The importance of HRV as a risk stratifier has been well accepted, particularly in survivors of myocardial infarction. Large clinical trials are still needed to clarify the role of HRV in patients with non-ischemic cardiomyopathy. Given the significant association between HRV and the development of fatal arrhythmias/sudden cardiac death, HRV has been used in some clinical trials as one of the screening tests to select optimal candidates for implantable cardioverter–defibrillator placement, although its role in this area has not been fully established. Additional large prospective clinical trials are needed to further clarify the predictive value of existing or novel HRV parameters, on their own or in combination with other risk stratifiers, for assessing the risk of sudden cardiac death in a variety of clinical settings.

---

Despite significant advances in medical and device therapy, sudden cardiac death (SCD) remains a major issue in public health, with an estimated annual rate of up to 450,000 in the US.¹ Implantable cardioverter–defibrillator (ICD) therapy is effective for both primary^2,3 and secondary prevention of SCD3 in patients with prior myocardial infarction (MI) and poor left ventricular (LV) function. In patients with non-ischemic cardiomyopathy, ICD therapy also significantly reduces allcause mortality⁴ and potentially improves long-term prognosis in selected patients.^5,6 However, if ICDs were implanted in all Multicenter Automatic Defibrillator Implantation Trial (MADIT)-IIeligible patients, the number needed to treat to save one life would be too high,⁷ and existing healthcare systems cannot afford increased ICD usage.

Given the invasive nature and possible complications^6,8 of ICD implantation and the fact that not all patients experience recurrent malignant ventricular tachyarrhythmias after ICD implantation,⁹ it is imperative to identify those patients who are at the highest risk for life-threatening arrhythmias and who would benefit most from ICD therapy in addition to optimal medical treatment.

Risk Stratification for Implantable Cardioverter-Defibrillators
The most commonly used and well-defined tests for predicting major arrhythmic events include measurement of LV function, evaluation of autonomic modulation, and detection of arrhythmic markers. LV function is usually assessed by measuring LV ejection fraction (LVEF) using echocardiography or ventriculography. Reduced LVEF has been commonly used as the first selection criterion for ICD implantation,² but there has not been an easy algorithm derived from LVEF and other clinical characteristics that can predict those patients who will benefit most from ICD therapy.

Markers for arrhythmia substrate include, but are not limited to, the frequency of ventricular ectopic beats >10 per hour (VE10), non-sustained ventricular tachycardia (VT) on Holter monitoring electrocardiogram (ECG), and signal-averaged ECG (SAECG). These tests have been frequently applied to screen patients for further invasive testing before an ICD is implanted.¹⁰

View Article here