Effects ofIntravenous andChronic Oral Verapamil Administration inPatients withSupraventricular Tachyarrhythmias

SUMMARY Theefficacy ofi.v. andoralverapamil was studied in28patients withsupraventricular tachycardia (SVT). Verapamil (5-10 mg i.v.) terminated SVT inallsixpatients withatrioventricular nodal (AVN)reentrant tachycardia. Inallpatients verapamil prolonged antegrade butdidnotaffect retrograde AVN conduction time. Twopatients hadassociated sinus nodal reentrant tachycardia thatpersisted after the AVN tachycardia terminated. Insixpatients withSVTusing an accessorypathway forretrograde conduction, i.v. verapamil terminated SVTinfourandslowed SVTintwopatients. Verapamil didnotaffect theelectrophysiologic properties ofthe accessorypathway andtheeffect ontheSVT,aswithAVN reentry, wascaused bychanges inantegrade AVN function. Verapamil lengthened AVN antegrade conduction timeinpatients withaccessory pathways less than itdidinpatients withAVN reentry. Verapamil atdoses that resulted inAVN Wenckebach block hadnoeffect onthedischarge rateofthethree patients withautomatic atrial tachycardia. In13of14patients withatrial fibrillation orflutter, i.v. verapamil promptly decreased theventricular rate. Onepatient withpreexcitation hadan increase inventricular rate after verapamil. Theshortest RR intervals before andafter verapamil were260and220msec,respectively, and after verapamil more ventricular beats werepreexcited. Oralverapamil was given to19of28patients. Tendiscontinued thedrugwithin 30daysbecause ofside effects orineffectiveness. Seven patients treated fora mean of19months haveshownevidence ofimprovement, judged bydecreased frequency andshorter duration oftachycardia whenitdidrecur.Thus, i.v. verapamil isan effective antiarrhythmic drugformostpatients withSVT,butoralverapamil iseffective inonlyselected patients. VERAPAMIL hasbeenusedtotreat supraventricular tachycardia (SVT)forseveral years inEurope andrecently hasbeenapproved forinvestigational use intheUnited States.' Inthis study weassessed its efficacy andsafety andevaluated its electrophysiologic mechanism ofaction inpatients with different types of SVT.