Surprisingly more nonsustained VT shown in HCM using extended ECG monitoring

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, Dr. 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 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, Dr. 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, Dr. 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-hour and 30-day 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 Dr. 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.

Dr. van Gelder echoed Dr. 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. Dr. Caro Codón and Dr. van Gelder reported no relevant financial relationships.

A version of this article first appeared on Medscape.com.