Risk Stratification for Sudden Cardiac Death: Too Late to Establish a Role for Cardiac MRI?
Automatic detection and transvenous or subcutaneous defibrillation of malignant ventricular arrhythmias by implantable cardioverter defibrillators are vital for management of patients at high risk for sudden cardiac death. Guidelines and appropriate use criteria based on data from several clinical trials support prophylactic defibrillator implantation in patients with symptoms of heart failure and left ventricular ejection fraction ≤35%. Yet, existing guidelines direct defibrillator implantation to a small subset of the overall population at risk for sudden death, and with an average annual appropriate shock rate of 5.1%, many patients that receive an implantable defibrillator never require appropriate therapies and are exposed to device related risks. The recent Defibrillator Implantation in Patients with Non-Ischemic Systolic Heart Failure (DANISH) trial found no mortality benefit with prophylactic defibrillator implantation in patients with symptomatic heart failure and non-ischemic cardiomyopathy. Thus, additional data are necessary to refine patient selection among non-ischemic cardiomyopathy patients that currently meet defibrillator implantation criteria. At the same time, criteria to identify high risk of sudden cardiac death among patients that are currently excluded must evolve. As many as 80% of those who experience out of hospital cardiac arrests would not meet current criteria for primary prevention defibrillator implantation prior to the event. These patients, which generally have preserved or nearly preserved cardiac function, have lower mortality risks competing with sudden cardiac death and stand to derive significant benefit from defibrillator implantation. Currently utilized measures of sudden cardiac death risk, however, are based upon cardiac function rather than identification of the substrate for malignant arrhythmia. The left ventricular ejection fraction is readily quantifiable by echocardiography and has been used as the primary stratification tool in all major trials. But it is highly dependent on loading conditions, and is only an effective predictor of sudden cardiac death in subgroups of patients with direct association between scar extent and cardiac function.
- mid-wall fibrosis
- dilated cardiomyopathy
- sudden cardiac death
- late gadolinium enhancement
- cardiovascular magnetic resonance imaging
- implantable cardioverter-defibrillator
- Received March 20, 2017.
- Accepted March 24, 2017.