The basic pacing interval (S1-S1) was set at 300 ms, which was shorter than the cycle length of the spontaneous heart rate. Excitation threshold measurement followed each series of PES. After a train of 15 pacing stimuli, a single extrastimulus (S2) was delivered by shortening the S1-S2 interval in 5 ms steps until arrhythmia or refractoriness occurred. If S2 failed to induce arrhythmia, double extrastimuli (S2 and S3) were delivered with the S1-S2 interval just exceeding the ERP. S3 was introduced initially at the same interval as S2, which was again decreased in 5 ms steps. If S3 failed to induce arrhythmia, a third extrastimulus (S4) was delivered similarly. In most dogs, arrhythmias such as ventricular fibrillation (VF), sustained VT, nonsustained VT or premature ventricular complexes (PVCs) were induced. More than three consecutive PVCs were defined as VT. Nonsustained VT was defined as a VT lasting less than 30 s, while sustained VT was defined as a VT lasting more than 30 s.
Dogs in which ventricular arrhythmia was induced by PES at least twice during the control period were used further for pharmacological analysis. Sustained VT or VF was terminated by using a direct current defibrillator. After drug administration, the same procedure of PES was repeated. Twenty-four hour ECG recording: Del Mar Avionics ambulatory ECG recording devices (Model 456A, Irvine, California, USA) were used to record 24 h ECG of conscious beagles. Ten dogs for all experiments were given an oral capsule of vehicle (placebo), then at least two days afterward, oral class III drugs were tested. ECGs were printed out and the number of beats and the appearance of abnormal beats including PVCs and aberrant ventricular conduction were evaluated. Visiting an online pharmacy has never been easier and safer, since now you have the one you can call your favorite one: purchase cialis checkout now at the pharmacy that always takes care of its customers and always pay less money.