Handheld 6-lead ECG monitoring versus standard care for arrhythmia detection in patients receiving proarrhythmic medications: the HELP-C randomised trial

Introduction Proarrhythmic medications, including anticancer agents and Class Ic/III antiarrhythmics, need cardiac rhythm surveillance. Standard outpatient monitoring relies on infrequent clinic-based electrocardiograms (ECGs), which may fail to capture intermittent events. Handheld consumer-grade 6-lead ECG devices enable patient-initiated ambulatory rhythm recording and are recognised as a clinically relevant monitoring modality by current guidelines. Methods This multicentre, prospective, randomised controlled trial enrolled patients receiving proarrhythmic medications across three tertiary hospitals. Participants were randomised to ECG monitoring or standard care. Over 3 (±1) months, ECG monitoring participants recorded a 30-second 6-lead ECG at least weekly or when symptomatic. Both groups underwent mandatory 6-lead ECG at enrolment and final visit; standard care participants received no interim recordings. The primary endpoint was arrhythmia detection rate, defined exclusively by 6-lead ECG rhythm analysis: (1) atrial fibrillation/flutter, premature atrial/ventricular contractions, or other rhythm disorders; (2) bradycardia (<50 bpm) or tachycardia (>100 bpm); (3) prolonged absolute intervals (PR >200 ms, QRS >140 ms, QTc >440/450 ms [male/female]); or (4) significant relative changes from baseline (PR or QRS ≥25% increase, QTc >20 ms increase). Subgroup analyses included anticancer drug, Class Ic, and Class III antiarrhythmic recipients. Groups were compared by per-protocol analysis. Results Of 599 enrolled participants (ECG monitoring n=297, standard care n=302), 573 were analysed per protocol. Arrhythmia detection was significantly higher in the ECG monitoring group across nearly all endpoint components, including atrial fibrillation/flutter (AF, 40.0% vs. 15.7%, p<0.001) and QTc prolongation (46.8% vs. 7.2%, p<0.001). In subgroup analyses, ECG monitoring demonstrated higher detection rates across nearly all endpoints including AF (36.2% vs. 12.1%, p<0.05; 64.5% vs. 35.2%, p<0.005) and QTc prolongation (41.8% vs. 6.5%, p<0.05, 64.5% vs. 13.0%, p<0.5) both in Class Ic and III antiarrhythmic recipients. In the anticancer drug subgroup, QTc prolongation was significantly higher in the ECG monitoring group (40.9% vs. 0.0%, p<0.001). Conclusion Handheld 6-lead ECG monitoring significantly increased arrhythmia detection across nearly all rhythm categories compared with standard care in patients receiving proarrhythmic medications. Findings were consistent in antiarrhythmic subgroups, and QTc prolongation was significantly elevated in the anticancer drug subgroup. These results support handheld ECG monitoring as an effective cardiac surveillance strategy in this high-risk population.