Long QT Syndrome Type 1 and 2 Patients Respond Differently to Arrhythmic Triggers – The TriQarr In Vivo Study

Background
In patients with long QT syndrome (LQTS), swimming and loud noises have been identified as genotype-specific arrhythmic triggers in LQTS type 1 and LQTS type 2, respectively.

Objective
To compare LQTS groups’ responses to arrhythmic triggers.

Methods
LQTS1 and LQTS2 patients were included. Before and after beta blocker intake, electrocardiograms were recorded as participants: 1) were exposed to a loud noise of ∼100 dB. 2) immersed face into cold water.

Results
Twenty-three patients (9 LQTS1 and 14 LQTS2) participated. In response to noise, LQTS groups increased heart rate similarly, but LQTS2 patients prolonged their QTcF (Fridericia) significantly more than LQTS1: 37±8 vs. 15±6 ms (p=0.02). After intake of beta blocker, the QTcF prolongation in LQTS2 patients was significantly blunted and similar to LQTS1 (p=0.90).
In response to simulated diving, LQTS groups experienced a heart rate drop of ∼28 bpm, which shortened QTcF similarly in both groups. After intake of beta blockers, heart rate dropped 28±2 bpm in LQTS1 patients and 20±3 bpm in LQTS2, resulting in slower heart rate in LQTS1 compared with LQTS2 (p=0.01). In response, QTcF shortened similarly in LQTS1 and LQTS2 patients: 57±9 vs. 36±7 ms (p=0.10).

Conclusion
When exposed to noise, LQTS2 patients prolonged their QTc significantly more than LQTS1 patients. Importantly, beta blockers reduced the noise-induced QTc prolongation in LQTS2 patients — demonstrating the protective effect of beta blockers. In response to simulated diving, LQTS groups responded similarly, but a slower heart rate was observed in LQTS1 patients during simulated diving after beta blockers.