PR RR INTERVAL RATIO DURING RAPID ATRIAL-PACING - A SIMPLE METHOD FORCONFIRMING THE PRESENCE OF SLOW AV NODAL PATHWAY CONDUCTION/

Introduction: Although the AV conduction curve in patients with AV nod al reentrant tachycardia (AVNRT) is usually discontinuous, many patien ts with this arrhythmia do not demonstrate criteria for dual AV nodal pathways. During rapid atrial pacing, the PR interval often exceeds th e pacing cycle length when there is anterograde conduction over the sl ow pathway and AVNRT is induced. The purpose of this prospective study . was to determine the diagnostic value of the ratio of the PR interva l to the RR interval during rapid atrial pacing as an indicator of ant erograde slow pathway conduction in patients undergoing electrophysiol ogic testing. Methods and Results: The PR and RR intervals were measur ed during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction in four study groups: (1) patients with inducible AV nod al reentry and the classical criterion for dual AV nodal pathways duri ng atrial extrastimulus testing (AVNRT Group 1); (2) patients with ind ucible AV nodal reentry without dual AV nodal pathways (AVNRT Group 2) ; (3) control subjects less than or equal to 60 years of age without i nducible AV nodal reentry; and (4) control subjects > 60 years of age without inducible AV nodal reentry. For both groups of patients with i nducible AV nodal reentry, AV conduction was assessed before and after radiofrequency ablation of the slow AV nodal pathway. Before slow pat hway ablation, the PR/RR ratio exceeded 1.0 in 12 of 13 AVNRT Group 1 patients (mean 1.27 +/- 0.21) and 16 of 17 AVNRT Group 2 patients (mea n 1.18 +/- 0.15, P = NS Group 1 vs Group 2). After slow pathway ablati on, the maximum PR/RR ratio was < 1.0 in all AVNRT patients (Group 1 = 0.59 +/- 0.08, P < 0.00001 vs before ablation; Group 2 = 0.67 +/- 0.1 1; P < 0.00001 vs before ablation). Among both groups of control subje cts, the PR/RR ratio was > 1.0 in only 3 of 27 patients with no relati on to patient age. Conclusion: The ratio of the PR interval to the RR interval during rapid atrial pacing at the maximum rate with consisten t 1:1 AV conduction provides a simple and clinically useful method for determining the presence of slow AV nodal pathway conduction. This fi nding may be particularly useful in patients with inducible AV nodal r eentry without dual AV nodal physiology on atrial extrastimulus testin g.