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Myocardial fibrosis on cardiac MRI identified cardiomyopathy patients at high risk of sudden cardiac death and in need of an implantable cardioverter-defibrillator (ICD), data from a prospective trial showed.

ICD discharges occurred in 14% to 29% of patients with fibrosis revealed by late gadolinium enhancement. In contrast, no discharges occurred in patients without fibrosis on cardiac MRI, investigators reported in the Feb. 15 issue of the Journal of the American College of Cardiology.

The findings have implications for more efficient use of ICDs in patients with cardiomyopathy.

"We demonstrated a strong association between myocardial late gadolinium enhancement and appropriate ICD therapy, supporting the assertion that ventricular scar is an important arrhythmic substrate in cardiomyopathy," Leah Iles, MD, of Alfred Hospital in Melbourne, Australia, and co-authors wrote in conclusion.

"In addition, patients without late gadolinium enhancement had no appropriate device therapies, suggesting it may be possible to identify a low-risk patient subgroup that could be managed conservatively."

Current clinical guidelines use impaired left ventricular ejection fraction (LVEF) as the basis for recommendations about ICD use in cardiomyopathy. The recommendations have the potential to make 500,000 Medicare beneficiaries candidates for ICDs, at an estimated cost as high as $100,000 per quality-adjusted life year, the authors wrote in the introduction to their findings.

Most ICD recipients never receive device therapy, reflected in an estimated ICD-discharge rate of 5.1% per year, they continued.

A subgroup of patients with low LVEF appears to have a low risk of sudden death, although methods to identify them remain largely unvalidated. Recent studies have indicated that myocardial fibrosis on cardiac MRI is associated with poor prognosis in heart failure. Moreover, myocardial fibrosis has been linked to arrhythmias in both ischemic and nonischemic cardiomyopathy.

Late gadolinium enhancement may represent macroscopic regions of myocardial fibrosis, which are observed in about 30% of patients with nonischemic cardiomyopathy. The authors hypothesized that the absence of late gadolinium enhancement on cardiac MRI predicts a low risk of ICD discharge in patients who received the devices for primary prevention of sudden cardiac death.

To test their hypothesis, the authors prospectively evaluated 103 patients who received ICDs in accordance with current clinical guidelines. All the patients underwent cardiac MRI prior to device implantation, and the presence of regional myocardial fibrosis was determined by late gadolinium enhancement.

ICD implantation and cardiac MRI were performed in a uniform manner, and choice of ICD was left to the treating physician.

The study population comprised 61 patients with nonischemic cardiomyopathy and 42 with ischemic cardiomyopathy. Mean LVEF was 26% for the entire study population and did not differ by the origin of cardiomyopathy.

Late gadolinium enhancement identified regional myocardial fibrosis in 31 patients with nonischemic cardiomyopathy and in all 42 patients with cardiomyopathy of ischemic origin.

During a median follow-up of 573 days, ICD discharges occurred in nine of the 31 (29%) patients with nonischemic cardiomyopathy and regional fibrosis and in six (14%) patients with ischemic cardiomyopathy, a difference that did not achieve statistical significance. However, the incidence of ICD discharge was significantly higher in both groups with regional fibrosis compared with patients who had no evidence of fibrosis on cardiac MRI (P<0.01, P=0.04).

LVEF was similar in patients with and without myocardial fibrosis.

In an editorial, James Willerson, MD, of the University of Texas at Houston, agreed that the findings supported the authors' hypothesis. However, he cited a need for validation in a larger number of patients, as well as closer examination of patients who had fibrosis but no ICD discharge.

"In future studies, it would be important to quantify the volume of fibrosis in patients with and without appropriate ICD discharges," Willerson wrote.

"It would also be helpful to compare the degree of hypertrophy and frequency of nonsustained ventricular tachycardia with the predictive ability of fibrosis detection by late gadolinium enhancement and to determine whether there is additive predictive power in combining the three methods."