VANCOUVER, B.C. – The volume of denervated myocardium after a heart attack predicts the likelihood of sudden cardiac death and the need for an implantable defibrillator, according to results from a prospective, 4-year observational study.
"In this study, we found that in patients with ischemic cardiomyopathy who are eligible for an ICD [implantable cardioverter defibrillator], the volume of denervated myocardium predicts sudden death. It’s independent of more traditional endpoints that have been used," such as B-type natriuretic peptide, left ventricular ejection fraction, and New York Heart Association (NYHA) class. "Thus, molecular imaging may improve risk stratification for current ICD candidates," said investigator and cardiologist Dr. Michael E. Cain, dean of the School of Medicine and Biomedical Sciences, University at Buffalo (N.Y.).
The goal of the study is to better predict who will benefit from a defibrillator, he said at the 18th World Congress on Heart Disease.
He and his fellow investigators at the university found that about 30% of post-MI patients with more than 33% of their left ventricle denervated experienced arrhythmic death or – in those who had them – a defibrillator discharge for ventricular tachycardia or fibrillation greater than 240 beats per minute within 4 years of their heart attack; on average, about 6.7% met those endpoints each year.
In contrast, only about 5% of patients with less than 22% left ventricular sympathetic denervation met those endpoints, as did about 10% of those with 22%-33% left ventricular denervation, as assessed by myocardial response to a norepinephrine analogue on positron emission tomography. Denervated myocardium had a hazard ratio of 3.5 for sudden cardiac arrest or equivalent in the trial (P = .001).
Thirty-three of 204 post-MI patients experienced arrhythmic death or defibrillator discharge during the project. Most of the patients had undergone initial revascularization, and all were eligible for defibrillators at baseline. Overall, they were in their mid-60s, with left ventricular ejection fractions of about 26% and greater than NYHA class II heart failure. There were no significant demographic differences between patients who did and did not meet the study’s endpoints.
Prediction of sudden cardiac death events was even better when denervation was used in conjunction with three other factors: increase in the left ventricular end-diastolic volume index, creatinine greater than 1.5 mg/dL, and lack of angiotensin-converting enzyme inhibitor or angiotensin II receptor antagonist therapy.
Four-year event-free survival was about 98% in patients with none of those risk factors, about 85% in patients with one, and 50% in patients with two or more. The volume of infarcted or hibernating myocardium did not predict sudden cardiac arrest.
"The proven metric is left ventricle ejection fraction," but it and the many other methods that have been tried "have good negative predictive accuracy but not that good positive predictive accuracy, and so you are putting in defibrillators for people who don’t need them," he said.
For now, however, it would be "a leap of faith from a study that was prospective and observational" to actually use denervation "to determine therapies," he said.
Dr. Cain reported having no disclosures.