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Autonomic Control of Heart Rate and QT Interval Variability Influences Arrhythmic Risk in Long QT Syndrome Type 1 | Journal Scan
Study Questions:
Why do family members carrying the same mutation of the long QT syndrome (LQTS) have divergent symptoms and clinical outcomes?
Methods:
Holter recordings were performed in 46 members of 25 families constituting the South African LQT1 founder population carrying the KCNQ1-A341V mutation. Of these, 32 members had the mutation, and 14 did not. Mutation carriers were subdivided into symptomatic mutation carriers (SMCs) and asymptomatic mutation carriers (AMCs). The authors assessed the effect of circadian rhythm and of beta-blocker therapy over traditional time and frequency domain RR and QT variability indices.
Results:
The AMCs differed significantly from SMCs and from noncarriers in less vagal control of heart rate and more reactive sympathetic modulation of the QT interval, particularly during the daytime when arrhythmia risk for LQT1 patients is greatest.
Conclusions:
The present data identify an additional factor contributing to the differential arrhythmic risk among LQT1 patients carrying the same mutation. A “normal” autonomic control confers a high risk, whereas patients with higher sympathetic control of the QT interval and reduced vagal control of heart rate are at lowest risk.
Perspective:
AMCs have a greater degree of sympathetic modulation directed to the ventricles than SMCs, especially during the daytime, when the arrhythmic risk for LQT1 patients is higher. Counter to expectations, this suggests that greater sympathetic drive to the ventricles is protective in LQT1. These fascinating new findings may lead to more accurate risk stratification within LQTS families, and more targeted treatments.
Keywords: Long QT Syndrome, Arrhythmias, Cardiac, Circadian Rhythm, Heart Rate, Mutation, Autonomic Nervous System
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