Key result
Long QT syndrome patients had significantly higher QT variability (38 vs 19 msec, P=0.0001) and T wave complexity than unaffected family members, despite similar heart rate variability.
Why the study?
Dynamics of ventricular repolarization may contribute to cardiac arrhythmias in subjects with long QT syndrome, but detailed assessment of repolarization duration and complexity dynamics was needed.
Do repolarization dynamics (QT variability and T wave complexity) differ between patients with long QT syndrome and unaffected family members?
Observational (n=58)
Do repolarization dynamics (QT variability and T wave complexity) differ between patients with long QT syndrome and unaffected family members?
Absolute Event Rate: 38% vs 19%
p-value: p=0.0001
LQTS patients exhibit significantly increased variability in QT interval and T-wave complexity despite similar heart rate variability, suggesting altered repolarization dynamics may increase arrhythmia vulnerability.
INTRODUCTION: Dynamics of ventricular repolarization may contribute to cardiac arrhythmias in subjects with the long QT syndrome (LQTS). The aim of the present study was to assess the dynamics of repolarization duration and the dynamics of repolarization complexity in LQTS patients and their unaffected family members. METHODS AND RESULTS: Twelve-lead 24-hour ambulatory ECG recordings were obtained from LQTS patients (n = 38) and unaffected family members (n = 20). The 24-hour dynamics of the QT interval, T wave complexity (TWC) index measured by principal component analysis, and the RR interval were analyzed using standard deviation (SD) and square root of the mean squared differences of successive values of the parameters (RMSSD). QT variability, mean TWC, and TWC variability were increased in the LQTS patients compared with unaffected family members (QT-SD: 38 +/- 20 msec vs 19 +/- 7 msec, P = 0.0001; QT-RMSSD: 36 +/- 20 msec vs 14 +/- 8 msec, P = 0.0001; TWC: 27.7% +/- 11.1% vs 20.4% +/- 6.7%, P = 0.003; TWC-SD: 6.7% +/- 2.8% vs 4.6% +/- 1.8%, P = 0.003; TWC-RMSSD: 5.3% +/- 2.8% vs 3.7% +/- 1.2%, P = 0.004, respectively). At the same time, the measures of heart rate variability were similar between the affected and unaffected LQTS subjects (SD of normal-to-normal RR intervals [SDNN]: 94 +/- 25 msec vs 89 +/- 37 ms, P = 0.56; RMSSD: 49 +/- 26 msec vs 49 +/- 34 ms, P = 0.97, respectively). CONCLUSION: Despite similar heart rate variability, QT variability and the variability of TWC are significantly increased in LQTS patients compared with unaffected family members, suggesting that disturbances in temporal dynamics of repolarization and repolarization complexity in LQTS patients possibly increase vulnerability to arrhythmias.
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Perkiömäki et al. (2002) conducted an observational in Long QT Syndrome (LQTS) (n=58). Long QT Syndrome (LQTS) vs. Unaffected family members was evaluated on QT variability (QT-SD) (p=0.0001). Long QT syndrome patients had significantly higher QT variability (38 vs 19 msec, P=0.0001) and T wave complexity than unaffected family members, despite similar heart rate variability.
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