To study the mechanism of ventricular arrhythmias, the effect of dipyridamole (DIP; 300 mg/day), an adenosine transport inhibitor, on ventricular premature contractions (VPCs) was assessed in 12 patients who showed VPCs (21312 +/- 12314/day) on Holter ECG in a controlled setting. The effects were compared with those of verapamil (240 mg/day) and bisoprolol (5 mg/day). DIP suppressed more than one-half the VPCs in 5 patients. The mean degree of reduction in these DIP-responders was 75 +/- 18%. Both verapamil and bisoprolol inhibited VPCs in all of the DIP-responders (verapamil: 71 +/- 15%, bisoprolol: 88 +/- 16%). Two of the 5 DIP-responders had sustained ventricular tachycardias (VT) that were terminated by intravenous DIP, ATP, acetylcholine, verapamil, and propranolol. In contrast, verapamil did not inhibit VPCs in any of the DIP-nonresponders. Bisoprolol also did not suppress VPCs in 3 of 6 DIP-non responders. heart rate was unaffected by DIP, but was suppressed by both verapamil and bisoprolol. In addition, DIP increased the serum concentration of adenosine (control 16.3 +/- 17.1 vs 22.3 +/- 19.0 pmol/ml after DIP, p < 0.05). The inhibitory effect of DIP may involve suppression of Ca+2 current through an extracellular increase in adenosine.
The effects of adenosine triphosphate (ATP) on ventriculoatrial (VA) conduction were examined before and after accessory pathway (AP) ablation, with emphasis on assessment of the complication of dual atrioventricular (AV) node pathway. By evaluating the differences in the response to ATP of APs and other pathways, we assessed the usefulness and problems of this method. Of 59 patients who underwent AP ablation, 31 showed pre-excitation and 28 had concealed APs. A dual AV node pathway was found in 9 patients (15.3%) before ablation. After ablation, a dual AV node pathway was newly found in 9 patients. Thus, the total number of patients with a dual AV node pathway was 18 (30.5%). VA conduction over APs was not blocked in 26 of 29 patients, but the remaining 3 APs were blocked transiently by ATP. ATP caused VA block over the AV node in 15 of 16 patients and a dual AV node pathway in all 11 patients. In contrast, VA conduction over the retrograde fast pathway was blocked in 9 of 14 patients with AV node re-entrant tachycardia. ATP has little effect on APs, so observation of the response to ATP provides a more reliable and useful means of evaluating successful ablation. With this method, however, it is important to consider the possibility of the presence of ATP-sensitive APs and ATP-resistant retrograde fast pathways. The influence of ablation-induced injury has not been fully clarified. It is therefore essential to take into account various data, including the comparison between data obtained before and after ablation.
The optimum potential of the slow pathway (SP) was investigated by determining the effectiveness and safety of high-radiofrequency catheter ablation to treat atrioventricular nodal reentrant tachycardia (AVNRT). The subjects consisted of 29 patients with AVNRT (11 men, with a mean age of 54 +/- 15 years). Three ablation methods were used: a) Method A used the earliest atrial activation site, which is retrograde to the slow pathway, b) Method SP used the SP potential, and c) Method SW, in which ablation was performed stepwise starting from the coronary sinus and moving toward the recording site of the His bundle potential. Five, 20, and 4 patients underwent Methods A, SP, and SW, respectively. The fewest number of applications was needed with Method SP (11 +/- 9, 6 +/- 4, and 13 +/- 9), and the delivered energy was also lowest with Method SP (9151 +/- 6119, 3712 +/- 2168, and 12183 +/- 4090 J, with Methods A, SP, and SW, respectively). In Method SP, the interval between the atrium and SP was significantly longer at sites which cured tachycardia, than at sites at which ablation was ineffective (88 +/- 26 vs 66 +/- 22 msec, p < 0.05). The SP potential showed a humped shape in 18 of 20 patients. Method SP was the most efficient ablation method for treating AVNRT.
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