Hidetaka Okazaki

Increase in heart rate after radiofrequency catheter ablation is mediated by parasympathetic nervous withdrawal and related to site of ablation.

To assess the mechanism for the increased sinus rate after radiofrequency catheter ablation performed for atrioventricular nodal reentrant tachycardia (AVNRT), we studied heart rate variability before and after radiofrequency catheter ablation in 17 patients with AVNRT and in 38 patients with an accessory pathway. The accessory pathway was located at the left ventricular free wall, the right ventricular free wall, or the posterior interventricular septum. An increased sinus rate was observed in patients with AVNRT or with the accessory pathway at the posterior septum or left free wall after radiofrequency ablation. In these groups, high-frequency power, root mean square of successive difference and percent of adjacent cycles that were more than 50 ms apart, all of which are indices reflecting parasympathetic nervous activity, were decreased. The ratio of low-frequency to high-frequency power reflecting sympathovagal balance, was increased in patients with AVNRT or with an accessory pathway at the posterior septum or left free wall. Increases in sinus rate were correlated with decreases in high-frequency power, and percent of adjacent cycles more than 50 ms apart that the increase in heart rate was due to parasympathetic nervous withdrawal.

Significance of abnormal root mean square voltages in signal averaged electrocardiogram as a reliable predictor of sustained ventricular tachycardia.

The late potential is useful to predict patients with sustained ventricular tachycardia (VT). However, because positive predictive value for sustained VT is low, the validity of late potential for screening the patients to be studied by electrophysiological tests was not high. We examined 923 cases, including 63 cases of sustained VT. When we separated patients showing abnormal values of the root mean square voltage of the QRS end part 40 milliseconds (RMS40) into four groups, there was a tendency of a higher incidence of sustained VT with lower value of RMS40. When we conducted electrophysiological tests on 121 cases without sustained VT, it turned out a high induction rate of sustained VT in patients with low RMS40 values (RMS40 < 10 microV, 67%; < 20 microV, 30%; 20 microV, < or = 5%). We conclude abnormally low value (less than 10 microV) of RMS40 can be useful for screening the late potential-positive cases who are high risk for inducible sustained VT.

Supernormal conduction in a case of mobitz type II atrioventricular block

A 52-year-old woman exhibited Mobitz type II atrioventricular block with right bundle branch block and 1:1 atrioventricular conduction at or slower than 80 beats/min. Electrophysiologic study revealed transient HV interval block followed by recovery from the block at shorter coupling intervals without prolongation of the H1H2 and H2V2 intervals, suggesting true supernormal conduction. Isoproterenol enhanced the supernormal conduction, with shortening of blocked intervals and recovery of atrioventricular conduction, while atropine caused their less marked enhancement. Linking (ie, retrograde concealment of the impulse to the distal His bundle region through the blocked right bundle branch) is considered a possible mechanism of supernormal conduction in this case.