Key result
During vasovagal syncope induced by head-up tilt, patients exhibited a loss of QT-R-R hysteresis and failure of QT prolongation (k = -1.3 ± 1.5) compared to controls (k = 4.1 ± 1.3).
Why the study?
How does the QT-R-R relationship change during head-up tilt test in patients with vasovagal syncope compared to controls?
Case-Control (n=36)
How does the QT-R-R relationship change during head-up tilt test in patients with vasovagal syncope compared to controls?
Absolute Event Rate: -1.3% vs 4.1%
Patients with vasovagal syncope exhibit a failure of QT prolongation and loss of QT-R-R hysteresis during the vasovagal reflex, which normalizes with metoprolol therapy.
May indicate vagal effects on repolarization in VVS; leaves open diagnostic or therapeutic utility pending prospective studies.
BACKGROUND: QT interval is influenced by preceding R-R intervals and autonomic nervous tone. Changes in QT intervals during vasovagal reflex might reflect autonomic modulation of ventricular repolarization; however, this issue has not been fully elucidated. This study aimed to evaluate dynamic response of QT interval to transient changes in R-R interval during vasovagal syncope (VVS) induced by head-up tilt test. METHODS: Eighteen patients with VVS and 18 age-and sex-matched controls were studied. All patients with VVS had a positive mixed-type response to head-up tilt and all controls had a negative response. CM5-lead digital electrocardiogram (ECG) was recorded and QT intervals were analyzed using Holter ECG analyzer. Using scatter plots of consecutive QT and the preceding R-R intervals, QT-R-R relations during tilt-up and tilt-back or during vasovagal reflex were independently fitted to an exponential curve: QT (second) = A + B x exp[k x R-R (second)]. RESULTS: During the tilt-up, A, B, and k did not differ between patients with VVS and controls. During the tilt back, k showed equivalent positive value compared to the tilt-up (4.1 +/- 1.3 vs -4.6 +/- 0.9) in controls. However, k remained negative (-1.3 +/- 1.5) during vasovagal reflex in patients with VVS. In six patients, in whom metoprolol was effective in eliminating VVS, QT-R-R relationship during the tilt-back became similar to that in controls. CONCLUSIONS: In patients with VVS, hysteresis of the QT-R-R relation is similarly shown during tilt-up as in controls, whereas this hysteresis is no longer evident and failure of QT prolongation is observed during VVS.
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Mizumaki et al. (2005) conducted a case-control in Vasovagal syncope (n=36). Head-up tilt test vs. Healthy controls was evaluated on QT-R-R relationship parameter k during tilt-back or vasovagal reflex. During vasovagal syncope induced by head-up tilt, patients exhibited a loss of QT-R-R hysteresis and failure of QT prolongation (k = -1.3 ± 1.5) compared to controls (k = 4.1 ± 1.3).
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