SNOWMASS, COLO. – Since the 2011 release of the current American College of Cardiology/American Heart Association guidelines on hypertrophic cardiomyopathy, several new evidence-based tools have emerged as being helpful in decision making regarding which patients should receive an implantable cardioverter-defibrillator (ICD) for primary prevention of sudden cardiac death, Dr. Rick A. Nishimura said at the annual Cardiovascular Conference at Snowmass.
These three tools – gadolinium-enhanced cardiovascular magnetic resonance imaging, a novel European risk score calculator, and a new appreciation of the importance of age-related risk – are most useful in the many cases of hypertrophic cardiomyopathy (HCM) where the cardiologist is on the fence regarding ICD placement because the patient doesn’t clearly meet the conventional major criteria for an ICD, according to Dr. Nishimura, professor of medicine at the Mayo Clinic in Rochester, Minn.
Dr. Rick A. Nishimura
Dr. Nishimura, a member of the writing panel for the current guidelines (Circulation. 2011 Dec 13;124[24]:2761-96), predicted these tools will be incorporated into the next iteration of the HCM guidelines.
Notably absent from Dr. Nishimura’s list of useful tools was genetic testing for assessment of SCD risk in a patient with HCM.
“You should not spend $6,000 to do a genetic study to try to predict who’s at risk for sudden death. It turns out that most mutations are neither inherently benign nor malignant. High-risk mutations come from high-risk families, so you can do just as well by taking a family history,” according to the cardiologist.
Dr. Nishimura explained that the clinical dilemma in trying to evaluate SCD risk in a patient who presents with HCM is that the overall risk is quite low – probably 1% or less per year in the total HCM population – yet HCM is the number-one cause of SCD in younger patients. And it can occur unpredictably years or decades after diagnosis of HCM.
While ICDs are of proven effectiveness in preventing SCD in patients with HCM, reliance solely upon the conventional risk predictors to identify those who should get a device is clearly inadequate. Those criteria have a positive predictive accuracy of less than 15%; in other words, roughly 85% of HCM patients who get an ICD never receive an appropriate, life-saving shock, Dr. Nishimura said.
“We have a lot of work left to do in order to better identify these patients. In our own data from the Mayo Clinic, 20%-25% of patients have inappropriate ICD shocks despite efforts to program the device to prevent such shocks. That’s especially common in younger, active patients with HCM, and when it occurs patients find it absolutely devastating,” according to the cardiologist.
As stated in the current guidelines, the established SCD risk factors that provide a strong indication for an ICD in a patient with HCM are prior documented cardiac arrest, ventricular fibrillation, or hemodynamically significant ventricular tachycardia. Additionally, risk factors which, in Dr. Nishimura’s view, probably warrant insertion of an ICD and, at the very least should trigger a physician-patient discussion about the risks and benefits of preventive device therapy, include a family history of HCM-related sudden death in a first-degree relative, massive left ventricular (LV) hypertrophy as defined by a maximum wall thickness of at least 30 mm, and recent unexplained syncope inconsistent with neurocardiogenic origin.
Less potent risk predictors where savvy clinical judgment becomes imperative include nonsustained ventricular tachycardia on 24-hour Holter monitoring, a hypotensive blood pressure response to exercise, and an increased LV wall thickness in a younger patient that doesn’t rise to the 30-mm standard. These are situations where gadolinium-enhanced MRI, consideration of patient age, and the European risk scoring system can help in the decision-making process, he said.
Gadolinium-enhanced MRI: Contrast-enhanced cardiovascular MRI with late gadolinium enhancement has emerged as a reliable marker of the myocyte disarray and interstitial fibrosis which serves as a substrate for ventricular arrhythmias. In a recent study of 1,293 HCM patients followed for a median of 3.3 years, the incidence of SCD events increased progressively with the extent of late gadolinium enhancement. Extensive late gadolinium enhancement, defined as involving at least 15% of LV mass, was associated with a doubled risk of SCD events in patients otherwise considered at low risk (Circulation. 2014 Aug 5;130[6]:484-95).
“This is probably going to become one of the key markers that can help you when you’re on the fence as to whether or not to put in an ICD. We’re getting MRIs with gadolinium now in all of our HCM patients. What matters is not gadolinium enhancement at the insertion of the left ventricle into the septum – a lot of people have that – but diffuse gadolinium enhancement throughout the septum,” Dr. Nishimura said.