Key result
Intravenous adenosine provoked a significantly greater increase in the QT interval during maximal bradycardia in patients with long QT syndrome compared to healthy controls (15.8% vs 1.5%, P<0.001).
Why the study?
Does an intravenous adenosine challenge test expose abnormal QT responses that distinguish patients with long QT syndrome from healthy controls?
Case-Control (n=38)
Does an intravenous adenosine challenge test expose abnormal QT responses that distinguish patients with long QT syndrome from healthy controls?
An adenosine challenge test provoking transient bradycardia and subsequent tachycardia can expose abnormal QT prolongation and notched T-waves, providing a potential bedside diagnostic tool for long QT syndrome.
May support adenosine challenge as LQTS diagnostic adjunct; hypothesis-generating, needs prospective validation before clinical adoption.
AIMS: As arrhythmias in the long QT syndrome (LQTS) are triggered by heart rate deceleration or acceleration, we speculated that the sudden bradycardia and subsequent tachycardia that follow adenosine injection would unravel QT changes of diagnostic value in patients with LQTS. METHODS AND RESULTS: Patients (18 LQTS and 20 controls) received intravenous adenosine during sinus rhythm. Adenosine was injected at incremental doses until atrioventricular block or sinus pauses lasting 3 s occurred. The QT duration and morphology were studied at baseline and at the time of maximal bradycardia and subsequent tachycardia. Despite similar degree of adenosine-induced bradycardia (longest R-R 1.7+/-0.7 vs. 2.2+/-1.3 s for LQTS and controls, P=NS), the QT interval of LQT patients increased by 15.8+/-13.1%, whereas the QT of controls increased by only 1.5+/-6.7% (P<0.001). Similarly, despite similar reflex tachycardia (shortest R-R 0.58+/-0.07 vs. 0.55+/-0.07 s for LQT patients and controls, P=NS), LQTS patients developed greater QT prolongation (QTc=569+/-53 vs. 458+/-58 ms for LQT patients and controls, P<0.001). The best discriminator was the QTc during maximal bradycardia. Notched T-waves were observed in 72% of LQT patients but in only 5% of controls during adenosine-induced bradycardia (P<0.001). CONCLUSION: By provoking transient bradycardia followed by sinus tachycardia, this adenosine challenge test triggers QT changes that appear to be useful in distinguishing patients with LQTS from healthy controls.
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Viskin et al. (2005) conducted a case-control in Long QT syndrome (n=38). Intravenous adenosine vs. Healthy controls was evaluated on QT interval increase during adenosine-induced bradycardia (%) (p=<0.001). Intravenous adenosine provoked a significantly greater increase in the QT interval during maximal bradycardia in patients with long QT syndrome compared to healthy controls (15.8% vs 1.5%, P<0.001).
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