EXPERT ANALYSIS FROM THE CARDIOVASCULAR CONFERENCE AT SNOWMASS
SNOWMASS, COLO. (FRONTLINE MEDICAL NEWS) – 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. Nishimura, a member of the writing panel for the current guidelines ( Circulation. 2011 Dec 13;124:2761-96 ), 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;130:484-95 ).
“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.
Because SCD risk increases linearly with greater maximal LV wall thickness, gadolinium-enhanced MRI is particularly helpful in assessing risk in a younger patient with a maximal LV wall thickness of, say, 26 mm, he added.
Age: A study by led by Dr. Barry J. Maron, the cochair of the 2011 guideline committee and director of the HCM center at the Minneapolis Heart Institute, provides a new understanding that prophylactic ICD implantation is not warranted in patients with HCM who present at age 60 or older. In their study of 428 consecutive patients presenting with HCM at age 60 or above, the investigators found during 5.8 years of follow-up that the incidence of arrhythmic sudden death events was just 0.2% per year ( Circulation. 2013 Feb 5;127:585-93 ).
“They’ve shown that if you look at patients age 60 or above who have HCM, the risk of sudden cardiac death is almost nonexistent. That’s incredibly important to remember. Sudden death is something that’s going to happen in the younger population, under age 30,” Dr. Nishimura emphasized.
European SCD risk prediction tool: This tool was hailed as a major advance in the current European Society of Cardiology guidelines on HCM ( Eur Heart J. 2014;35:2733-2779 ). The tool was incorporated into the guidelines. It is also available as a smartphone app.
The risk prediction tool ( Eur Heart J. 2014 Aug 7;35:2010-20 ) is a complex equation that incorporates seven predictive factors: age, maximal LV wall thickness, left atrial diameter, LV outflow tract gradient, family history of SCD, nonsustained VT, and unexplained syncope. After input on these seven factors, the equation spits out an individual’s estimated 5-year SCD risk. Based on the study of 3,675 consecutive HCM patients with a median 5.7 years of follow-up that was used to develop the risk equation, the current ESC guidelines state that an ICD is not warranted in HCM patients with a 5-year risk below 4%, device implantation should be considered in those whose risk is 4%-6%, and an ICD should be even more strongly considered in patients with a 5-year risk in excess of 6%.
“A lot of people across the pond are using this risk score. But there are some problems with it,” according to Dr. Nishimura.
In his view, it “doesn’t make much sense” to include left ventricular outflow tract gradient or left atrial diameter in the risk equation. Nor is unexplained syncope carefully defined. Also, the equation would be improved by incorporation of late gadolinium enhancement on MRI, left ventricular dysfunction, and presence or absence of apical aneurysm as predictive variables. But on the plus side, the European equation treats maximal LV wall thickness as a continuous variable, which is more appropriate than the single 30-mm cutoff used in the ACC/AHA guidelines.
The biggest limitation of the European prognostic score, however, is that it hasn’t yet been validated in an independent patient cohort, Dr. Nishimura said. He noted that when Dr. Maron and coworkers recently applied the European SCD risk equation retrospectively to 1,629 consecutive U.S. patients with HCM, the investigators concluded that the risk equation proved unreliable for prediction of future SCD events. Fifty-nine percent of patients who got an appropriate ICD shock or experienced SCD were misclassified as low risk and hence would not have received an ICD under the European guidelines ( Am J Cardiol. 2015 Sep 1;116:757-64 ).
Nonetheless, because of the limited predictive accuracy of today’s standard methods of assessing SCD risk, Dr. Nishimura considers application of the European risk score to be “reasonable” in HCM patients who don’t have any of the strong indications for an ICD.
“If it comes up with an estimated 5-year risk greater than 6%, I think it’s very reasonable to consider implantation of an ICD,” he said.
Dr. Nishimura observed that in addition to assessing SCD risk, cardiologists have two other separate essential tasks when a patient presents with HCM. One is to screen and counsel the first-degree relatives. The other is to determine whether a left ventricular outflow tract obstruction is present in a symptomatic patient and, if so, to improve symptoms by treating the associated hemodynamic abnormalities medically and if need be by septal ablation or septal myectomy.
He reported having no financial conflicts of interest regarding his presentation.