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[5]: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[30]: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[5]: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.