Unmasked Brugada pattern by ajmaline challenge in patients with myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) generates missplicing of the SCN5A gene, encoding the cardiac sodium channel (Nav 1.5). Brugada syndrome, which partly results from Nav 1.5 dysfunction and causes increased VF occurrence, can be unmasked by ajmaline. We aimed to investigate the response to ajmaline challenge in DM1 patients and its potential impact on their sudden cardiac death risk stratification.

Among 36 adult DM1 patients referred to our institution, electrophysiological study and ajmaline challenge were performed in 12 patients fulfilling the following criteria: (1) PR interval >200 ms or QRS duration >100 ms; (2) absence of complete left bundle branch block; (3) absence of permanent ventricular pacing; (4) absence of implantable cardioverter-defibrillator (ICD); (5) preserved left-ventricular ejection fraction >50%; and (6) absence of severe muscular impairment. Of note, DM1 patients with ajmaline-induced Brugada pattern (BrP) were screened for SCN5A.

In all the 12 patients studied, the HV interval was <70 ms. A BrP was unmasked in three patients but none carried an SCN5A mutation. Ajmaline-induced sustained ventricular tachycardia occurred in one patient with BrP, who finally received an ICD. The other patients did not present any cardiac event during the entire follow-up (15 ± 4 months).

Our study is the first to describe a high prevalence of ajmaline-induced BrP in DM1 patients. The indications, the safety, and the implications of ajmaline challenge in this particular setting need to be determined by larger prospective studies.