Electrophysiologic effects of ouabain in patients with preexcitation and circus movement tachycardia

Effects of intravenous ouabain were evaluated in 19 patients with an anomalous conduction pathway (14 with manifest and 5 with concealed preexcitation) utilizing intracardiac stimulation and recording. Anterograde conduction through the anomalous pathway was present in all 14 patients with manifest preexcitation at a maximal atrial paced rate of 140 to 250 beats/min (mean ± standard error of the mean 214 ± 7.2) before and at 150 to 240 beats/min (mean 206 ± 7.1) after ouabain (difference not significant [NS]). The anterograde effective refractory period of the anomalous pathway, measured at an equivalent atrial paced rate in 10 patients, was 250 to 450 ms (mean 309 ± 19.7) before and 260 to 450 ms (mean 300 ± 17.2) after ouabain (NS). Retrograde conduction through the anomalous pathway was possible at maximal ventricular paced rates (17 patients) of 160 to 250 beats/min (mean 222 ± 6.6) before and 190 to 250 beats/min (mean 221 ± 4.4) after ouabain (NS). Sustained atrioventricular (A-V) reentrant paroxysmal supraventricular tachycardia was inducible in all 19 patients before and in 17 patients (89 percent) after ouabain (tachycardia could not be induced in two patients because of increased A-V nodal refractoriness). The mean cycle length of tachycardia in the 17 patients was 320 ± 6.7 ms before and 340 ± 8.1 ms after ouabain (p <0.01). In conclusion, ouabain has no significant effect on either anterograde or retrograde anomalous pathway refractoriness. Although ouabain slightly increases the cycle length of tachycardia, it does not interfere with induction of tachycardia in most patients with preexcitation. Oral cardiac glycosides alone would appear to be of limited value in patients with preexcitation and recurrent supraventricular tachycardia.