The electrophysiologic effects of intravenous
diltiazem were evaluated in 10 patients with recurrent
supraventricular tachycardias. The
tachycardia incorporated an accessory pathway in 7 patients and was due to AV nodal reentry in 3 patients.
Diltiazem 0.25 mg/kg was administered intravenously over 5 minutes during sustained
supraventricular tachycardia. Programmed electrical stimulation was used to restore sinus rhythm if
diltiazem failed to terminate the
arrhythmia within 10 minutes. Conduction intervals, refractory periods and
tachycardia characteristics were evaluated before and immediately after
drug administration.
Diltiazem did not significantly modify sinus cycle length, AH and HV intervals. Atrial and ventricular effective refractory periods were similar before and after
diltiazem. The effective refractory period of the AV node was prolonged by 42 msec after
diltiazem (p less than 0.05).
Diltiazem increased the
tachycardia cycle length from 320 +/- 41 to 353 +/- 36 msec (p less than 0.01) but terminated the
arrhythmia in only 2 patients. After
diltiazem,
supraventricular tachycardia could not be reinitiated in only 2 patients and the
tachycardia initiating window was not significantly reduced (56 +/- 26 to 41 +/- 33 msec). The infusion of
diltiazem was accomplished without side effects. Thus, 0.25 mg/kg of intravenous
diltiazem produces a modest depression of AV nodal function and is not very effective in terminating
supraventricular tachycardia or preventing its initiation in this study population. Further studies using higher doses of intravenous
diltiazem would be useful to determine its maximal therapeutic benefit in patients with recurrent
supraventricular tachycardias.