DIPYRIDAMOLE SUPPRESSES CATECHOLAMINE-SENSITIVE AND CA-SENSITIVE VENTRICULAR ARRHYTHMIAS(+ INFLUX)

To study the mechanism of ventricular arrhythmias, the effect of dipyr idamole (DIP; 300 mg/day), an adenosine transport inhibitor, on ventri cular premature contractions (VPCs) was assessed in 12 patients who sh owed VPCs (21312 +/- 12314/day) on Holter ECG in a controlled setting. The effects were compared with those of verapamil (240 mg/day) and bi soprolol (5 mg/day). DIP suppressed more than one-half the VPCs in 5 p atients. 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 th e 5 DIP-responders had sustained ventricular tachycardias (VT) that we re terminated by intravenous DIP, ATP, acetylcholine, verapamil, and p ropranolol. 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 pm ol/ml after DIP, p<0.05). The inhibitory effect of DIP may involve sup pression of Ca++ current through an extracellular increase in adenosin e.