Noninvasive Risk Stratification for Sudden Cardiac Death

For now, LVEF is still the most useful basis for decisions about preventive intervention.

Sponsoring Organizations: American Heart Association, American College of Cardiology, Heart Rhythm Society

Background and Purpose: Accurate identification of individuals who are likely to die of cardiac arrhythmias would allow selective use of implantable cardioverter-defibrillators and other therapies to prevent sudden cardiac death (SCD). A vast amount of research energy has been spent in attempts to find noninvasive tests that can separate individuals into high-risk and low-risk groups. This scientific statement summarizes the findings of those studies.

Key Points:
1. Noninvasive tests evaluated to date measure:

• Slowed conduction (QRS duration, signal-averaged electrocardiogram)
  
• Variations in ventricular repolarization (QT interval, QT dispersion, T-wave alternans)
  
• Disparities in autonomic tone (heart rate variability, heart rate turbulence, heart rate recovery
  after exercise, baroreceptor sensitivity)
• Degree of myocardial damage (LV ejection fraction, 6-minute walk)
  
• Ventricular ectopy (long-term ambulatory monitoring)
  

2. In patients with ischemic or nonischemic cardiomyopathies, LVEF remains the best and possibly the only clinical test currently available to identify high-risk populations.

3. Patients with LVEF 35% are at the highest risk for SCD and, in the absence of comorbidities that severely shorten life expectancy, should undergo ICD implantation.

4. Most patients with LVEF 35% will not suffer SCD. However, at present, no noninvasive test has been proven to adequately identify low-risk patients with LVEF 35% who can be treated without an ICD.

5. Most SCDs occur in individuals with LVEF >35%. However, at present, no noninvasive test has been proven to adequately identify high-risk patients with a preserved LVEF who can be treated with an ICD.

6. In patients with hypertrophic cardiomyopathy, risk factors for SCD include history of resuscitated SCD or unexplained syncope, nonsustained ventricular tachycardia, hypotensive response to exercise, family history of SCD, and massively thick septum. None of the other noninvasive tests studied has been shown to add incremental value to these clinical features for risk stratification in these patients.

Comment:

Despite decades of sometimes quite promising research, LVEF measurement is the only clinically useful test to distinguish patients who need an ICD from those who do not. Although many of the other noninvasive tests studied show promise, at present none is sufficiently sensitive or specific to drive clinical decisions regarding ICD implantation. Such a tool would be most welcome, and we hope one or a combination of the tests described in this report will prove to be a more effective strategy in the coming years.

— Mark S. Link, MD

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