Fig. 4.

Tachybradycardia produced by prolonged isoproterenol and ZD infusion. Shown are pseudo-ECGs from the canine isolated RA. A: tachybradycardia from the first dog. Top, eight episodes of tachybradycardia; bottom, expanded view of the indicated section (*) showing 4.0- and 3.5-s pauses. B: tachybradycardia from a second RA. Top, three episodes of tachybradycardia; bottom, expanded view of the indicated section (*) showing a 4.2-s pause. C: comparison of the first and last CLs between pauses.