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Differential effects of adenosine on antegrade and retrograde fast pathway conduction in atrioventricular nodal
1Department of Internal Medicine, Kaohsiung Medical College, Taiwan, Republic of China.
Insights
Adenosine differentially affects atrioventricular (AV) and ventriculoatrial (VA) conduction in AV nodal reentry. It more potently slows antegrade fast pathway conduction than retrograde fast pathway conduction.
Area of Science:
- Cardiology
- Electrophysiology
- Pharmacology
Background:
- Adenosine is known to depress atrioventricular (AV) nodal conduction.
- The specific effects of adenosine on both antegrade and retrograde fast pathway conduction in AV nodal reentry tachycardia (AVNRT) remain incompletely understood.
- Previous studies have not fully elucidated the differential impact of adenosine on these pathways.
Purpose of the Study:
- To investigate the differential effects of adenosine on antegrade and retrograde fast pathway conduction in patients with AV nodal reentry.
- To compare the potency of adenosine in slowing conduction in the fast versus slow pathways of AVNRT.
- To assess the influence of verapamil on adenosine's effects on ventriculoatrial (VA) conduction.
Main Methods:
- Radiofrequency catheter ablation was used to selectively ablate the antegrade slow pathway in 17 patients with AVNRT.
- High right atrial pacing and right ventricular apical pacing were employed to assess antegrade and retrograde fast pathway conduction, respectively.
- Incremental intravenous doses of adenosine were administered until AV block or VA block occurred, with and without verapamil in a subset of patients.
Main Results:
- Adenosine required a significantly lower dose to produce AV block (3.4 mg) compared to VA block (8.2 mg), indicating greater potency for slowing antegrade fast pathway conduction.
- The increase in the atrio-His interval by 50% with adenosine was 1.8 mg, while the increase in the VA interval by 50% was 3.4 mg.
- Verapamil demonstrated an additive effect to adenosine in slowing retrograde VA conduction.
Conclusions:
- Adenosine exhibits differential potency in depressing AV and VA conduction in AV nodal reentry, more effectively slowing antegrade fast pathway conduction.
- The retrograde fast pathway in AVNRT appears to involve an AV nodal-like structure, as evidenced by verapamil's additive effect with adenosine.
- These findings clarify adenosine's electrophysiological effects in AVNRT and have implications for its clinical use.
Abstract:
Although adenosine depresses antegrade atrioventricular (AV) nodal conduction, the effects of adenosine on antegrade and retrograde fast pathway conduction in AV nodal reentry have not been determined. In 17 patients (five men, 12 women, mean age 49 +/- 12 years) with common slow-fast AV nodal reentrant tachycardia, the antegrade slow pathway conduction was selectively and completely ablated by radiofrequency catheter ablation while the antegrade and retrograde fast pathway conduction remained intact. During high right atrial pacing at a mean pacing cycle length of 474 +/- 36 msec, adenosine was rapidly injected intravenously at an initial dose of 0.5 mg followed by stepwise increases of 0.5 mg or 1.0 mg given at 5-minute intervals until second-degree AV block developed. During right ventricular apical pacing at the same pacing cycle lengths (mean 474 +/- 36 msec) as those in the study of antegrade conduction, intravenous injection of incremental doses of adenosine was repeated until ventriculoatrial (VA) block occurred. The adenosine-induced prolongation of VA conduction was also determined in the presence of verapamil (loading dose 0.15 mg/kg, maintenance dose 0.005 mg/kg/min) in seven of 17 patients. The dose of adenosine required to produce AV block, the increase in the atrio-His interval by 50% and the maximal response were 3.4 +/- 1.4 mg, 1.8 +/- 0.6 mg, and 58% +/- 5%, respectively. On the other hand, the dose of adenosine required to produce VA block, the increase in the VA interval by 50%, and the maximal response were 8.2 +/- 2.9 mg, 3.4 +/- 0.6 mg, and 20% +/- 5%, respectively, in the control and 3.7 +/- 0.5 mg, 3.5 +/- 0.7 mg, and 23% +/- 5%, respectively, in the presence of verapamil. In conclusion, adenosine has a differential potency to depress AV and VA conduction in patients with AV nodal reentry, with greater potency for slowing antegrade fast than retrograde fast pathway conduction. Verapamil had an additive effect to adenosine on slowing retrograde VA conduction, which further supports the evidence that the retrograde fast pathway in part involves an AV nodal-like structure.