| More than half of patients with pacemaker and implantable cardioverter-defibrillator receives antiarrhythmics in order to control tachycardia. It is known that some antiarrhythmics increase pacing threshold and cause pacing failure. Therefore, it is valuable to evaluate the effect of some common antiarrhythmics on pacing threshold and give clinicians advises regarding a possible relation between antiarrhythmic drugs and pacemakers. This study focused on the efficacy and safety of propafenone and amiodarone in dogs and patients. The clinic trial was established to observe the effect of routine dose propafenone or amiodarone on pacing threshold within 3 months after pacemaker implantation. The experiment research was set to increase the doses of propafenone or amiodarone gradually and to observe the effect of propafenone and amiodarone on the pacing threshold at larger doses.Methods: The experiment was performed in 12 adult mongrel dogs weighting 14.21±1.98Kg (13-17Kg). Under general anesthesia with intravenous barbital sodium (30mg/Kg), two electrical catheters were inserted into the right atrium and the right ventricle through jugular vein, respectively. The basic atrial and ventricular pacing threshold, sensing threshold and lead impedance, blood pressure, heart rate (HR), PR interval, QRS duration and QTc interval were obtained. Propafenone were intravenously administered in different doses (3.1mg/Kg, 3.1mg/Kg, 4.65mg/Kg, 4.65mg/Kg and 6.2mg/Kg) during a 20-minute period. After drugs, the parameters above were determined repeatedly. For the amiodarone group, the experimental procedures were same as the propafenone group and the doses were 10mg/Kg, 10mg/Kg, 15mg/Kg, 15mg/Kg, 20mg/Kg, respectively. In the clinical trial, 20 patients with permanent pacemaker received 2 intravenous doses of propafenone (70mg foreach), and the parameters above were determined following propafenone administration. These parameters were monitored at 0, 30, 60, 90, 120 minutes after drug administration. After 5 half-life time of propafenone, 2 doses (150mg for each) of amiodarone were intravenously given to the same patient. The chromatographic condition of propafenone and amiodarone with high performance liquid chromatography was established to determine serum concentrations of propafenone and amiodarone.Result: Experimental Study: With increasing of propafenone doses, mean blood pressure (MBP) and HR decreased, and PR interval, QRS duration and QTc interval prolonged gradually, and pacing threshold increased. When propafenone reached a dose of 6.2mg/Kg, MBP decreased and HR from 142±llmmHg to 67±12mmHg and 163±13 bpm to 90±10 bpm, respectively (all P<0.01), compared with the baseline. PR interval, QRS duration and QTc interval prolonged from 98±10ms to 159±28ms, 40±5ms to 102±22ms, 315±32ms to 366±18ms, respectively (all PO.01). Atrial and ventricular pacing threshold increased from 0.98±0.36V to 8.25±1.92V and 0.55±0.35V to 2.30±1.78V, respectively (all P<0.01). P or R amplitude decreased from 4.8±1.3mV to 1.6±0.7mV (P<0.01) and 20mV to 18.3±2.2mV (P<0.05), respectively.For amiodarone, MBP decreased from 134±21 to 59±21 mmHg (P<0.01) after the first dose. After administration of amiodarone, HR decreased, and PR interval, QRS duration and QTc interval prolonged gradually. Following the all 5 doses of amiodarone, HR decreased from 173±19 to 69±22bpm (P<0.01) and PR interval, QRS duration and QTc interval prolonged from 93±10ms to 134±13ms (P<0.01), 43±8ms to 90±21ms (P<0.01), 316±35ms to 322±21ms (P>0.05), respectively. Atrial or ventricular pacing threshold increased from 0.8±0.22V to 0.92±0.36V (P<0.01) and 0.40±0.12V to 0.5±0.11V (P>0.05).Clinic Trial: After drug administration, HR decreased, and PR interval,...
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