Surprisingly More NSVT Using Extended ECG Monitoring in HCM

Clinically important arrhythmias, especially nonsustained ventricular tachycardia (NSVT), may be more prevalent in patients with hypertrophic cardiomyopathy (HCM) than widely believed, suggests a study that questions current risk stratification practices in HCM.

In the registry study, such arrythmias were observed in about six times as many HCM patients during 30 days of ambulatory electrocardiographic (ECG) monitoring as would have been identified based on the first 24 hours of the monitoring period: 65% vs 11% of the cohort.

Also, about 62% of the patients showed NSVT at "extended" 30-day monitoring, compared with an 8% prevalence of the arrhythmia based on the more conventional ECG monitoring period of 24 hours.

Nonsustained ventricular tachycardia, an important arrhythmia used every day in clinical practice to make decisions, is "much, much more prevalent than we thought" in patients with HCM, Juan Caro Codón, MD, the study's principal investigator, told theheart.org | Medscape Cardiology. "We should invest in further research regarding extended ECG monitoring in these patients."

Caro Codón, of La Paz University Hospital, Madrid, Spain, presented the findings from the TEMPO-HCM study April 17 at the 2023 congress of the European Heart Rhythm Association, held in Barcelona and virtually.

Its results, he said, have implications for stratifying HCM patients according to their risk for sudden cardiac death in deciding who should be offered an implantable cardioverter-defibrillator (ICD).

The life-incidence of atrial fibrillation (AF) in patients like those in the current analysis has previously been found to be about 20%, and the life-prevalence of NSVT about 20% to 30%, using traditional 24- or 48-hour Holter monitoring, Caro Codón said.

"These arrhythmias are clinically relevant events because they are linked to very meaningful clinical endpoints," including stroke and thromboembolism, he said, "but also for sudden cardiac death."

Extended ECG monitoring has been shown useful in the setting of cryptogenic stroke and after AF ablation, but similar findings have been scarce in HCM. Patients using personal wearable monitors such as 'smart watches,' Caro-Codón said, have come to his clinic with concerns that the devices may have signaled a problem. But the lack of relevant data leaves them without a sufficient answer.

In other findings, invited discussant Isabelle van Gelder, MD, PhD, observed after Caro Codón's presentation that the number of patients with AF almost doubled based on extended monitoring compared to the first 24 hours of monitoring.

Based on ESC guidelines from 2020, "Once clinical AF has been documented, there is a class IIA recommendation to start anticoagulation," said van Gelder, University of Groningen, the Netherlands. "Therefore, your data really are a call for more data on screening for AF in hypertrophic cardiomyopathy patients."

Prospective Multicenter Registry

The TEMPO-HCM registry includes patients with HCM and a clinical indication for standard Holter monitoring at five hospitals in Spain. It excludes patients with HCM phenocopies and those implanted with ICDs.

Those in the current analysis underwent 30-day ECG monitoring with a small, wearable device that Caro Codón described as about 7 cm long, worn in what is essentially a T-shirt with a pocket. Patients could remove the shirt and device to bathe or go swimming, for example, and still be monitored for most of the day.

The analysis included the registry's first 100 patients (mean age 57 years; 78% male). Hypertension was present in 47%, 58% were on beta-blockers, 16% had prior AF or atrial flutter, and 19% were taking anticoagulants. Only 8% were on antiarrhythmic drugs, Caro Codón reported.

The patients had good functional status (68% and 29% were in NYHA class 1 and 2, respectively) and their left ventricular ejection fraction averaged 66%. Of the 71 patients who underwent MRI, 28.2% showed late gadolinium enhancement suggesting myocardial scarring.

More Arrhythmias on 30-day Monitoring

The primary endpoint of clinically relevant arrhythmia (AF, atrial flutter, or NSVT) was identified during the first 24 hours of monitoring in 11% of patients. The prevalence rose to 65% (P < .001) based on 30-day monitoring.

Similarly, prevalences of the composite primary endpoint components grew on extended monitoring, but the increases reached statistical significance only for NSVT; its prevalence went from 8% to 62% (P < .001). Prevalences rose nonsignificantly from 6% to 10% for AF and 0% to 1% for sustained ventricular tachycardia.

The incidence of NSVT during monitoring climbed fastest from day 0 through about day 19 and then rose more slowly through day 30, Caro Codón said. "It actually didn't reach a plateau during this time period, so there is the possibility that if we had continued monitoring patients, the difference between both periods may have been even higher."

Three variables predicted the incidence of nonsustained VT during monitoring, he said: age, atrial wall thickness, and whether there was late gadolinium enhancement at MRI.

An exploratory analysis looked at the 5-year risk of sudden cardiac death using the European Society of Cardiology (ESC) HCM-SCD risk calculator recommended in guidelines. Risk assessment based on the 30-day extended monitoring period, compared with the first 24 hours of monitoring alone, predicted a significantly higher 5-year risk of sudden death, Caro Codón said.

"Even more importantly," he added, "over 20%" of patients would have been reclassified into a higher-risk group and possibly considered for an ICD based on extended monitoring compared to 24-hour monitoring.

However, given that more than 50% of patients were found to have NSVT during extended monitoring, Caro Codón proposed that decisions on whether to implant an ICD should not be so "binary" based on the presence or absence of symptoms, and proposed further investigations be conducted into the complete phenotype of these arrhythmias.

The study has limitations, he observed, including a relatively small size; but it was able to detect important differences between 24 hours and 30 days monitoring outcomes even with only 100 patients. It was also limited by a lack of clinical follow-up for information on endpoints like stroke, thromboembolism, and sudden cardiac death.

Extended monitoring detected more cases of NSVT in the study's relatively low-risk HCM patients who would not generally have an indication for ICD implantation, observed van Gelder. Also, at present the prognostic value of NSVT for SCD "seems to be more important at younger age" — that is, younger than 30 years — in patients with HCM.

Van Gelder echoed Caro Codón’s call for more data from prolonged monitoring to help stratify patients according to risk; she proposed NSVT frequency, duration, and rate as possible targets.

The study was supported by an unrestricted grant from Nuubo, which provided the ECG monitoring systems. Caro-Codón and Van Gelder reported no relevant financial relationships.

European Heart Rhythm Association 2023: Late Breaking Science–Day 2. Extended ECG monitoring in HCM. Presented April 17, 2023.

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