Neural Control of Heart Rate Is an Arrhythmia Risk Modifier in Long QT Syndrome
Key result
Low resting HR and baroreflex sensitivity linked to ~74% fewer symptoms in KCNQ1-A341V carriers.
- P<0.05
- n=56
Why the study?
Clinical heterogeneity in long QT syndrome is unexplained, and it was hypothesized that differences in autonomic responses might modify clinical severity in LQT1 patients.
Population
56 KCNQ1-A341V mutation carriers in a South African LQT1 founder population
Comparison
Resting HR and BRS on and off beta-adrenergic blockers correlated to major cardiac events
Design
Observational study
Authors
Discussion
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Implication
Should not alter LQT1 management; leaves open causality and therapeutic potential of autonomic modulation in KCNQ1 carriers.
Key Points
- The central aim is to evaluate how autonomic responses influence the severity of long QT syndrome type 1 in KCNQ1 mutation carriers.
- Evaluated resting heart rate and baroreflex sensitivity in a South African founder population of long QT syndrome type 1 patients.
- Correlated cardiac events with heart rate and baroreflex sensitivity on and off beta-adrenergic blockers.
- Sample size included 56 mutation carriers.
- Mean resting heart rate was lower in asymptomatic patients (p < 0.05), indicating a protective effect.
- Lower heart rate tertile was associated with a reduced likelihood of prior cardiac events (OR 0.19, 95% CI 0.04 to 0.79, p < 0.02).
- Lower baroreflex sensitivity in asymptomatic patients (11.8 +/- 3.5 ms/mm Hg vs. symptomatic 20.1 +/- 10.9 ms/mm Hg, p < 0.05) suggests protective mechanisms.
Study Design
Type
Observational (n=56)
Structured PICO
P
Population
56 mutation carriers in a South African LQT1 founder population segregating the KCNQ1-A341V mutation
O
Outcome
Major cardiac events (symptomatic vs asymptomatic status)hard clinical
Main Result
Absolute Event Rate: 20% vs 76%
p-value: p=< 0.05
Lower resting heart rate and blunted baroreflex sensitivity act as protective physiological risk modifiers against major cardiac events in LQT1 patients with the KCNQ1-A341V mutation.
Cite This Study
Schwartz et al. (2008) conducted an observational in Long QT syndrome type 1 (LQT1) (n=56). Lower resting heart rate and baroreflex sensitivity vs. Higher resting heart rate and baroreflex sensitivity was evaluated on Symptomatic status (major cardiac events) (p=< 0.05). Being in the lower tertile for both resting heart rate and baroreflex sensitivity was associated with a significantly lower rate of symptoms in KCNQ1-A341V carriers (20% vs. 76%, p < 0.05).