Acute Effects of Anti-Anginal Drugs on Cardiac Pacing Threshold

Abstract

SUMMARY:
Forty cardiac pacing threshold studies were conducted in 25 patients being temporarily paced prior to permanent pacemaker implantation using the following anti-anginal drugs: Nitroglycerine 0.5 mg (7 patients), nifedipine 10 mg (7 patients) administered sublingually and intravenously administered (W) oxyfedrine 0.15 mg/kg (6 patients), propranolol 0.1 mg/kg (10 patients), and verapamil 0.15 mg/kg (10 patients). Changes in voltage (volts), current (mA), energy (micro-joules) and resistance (ohms) were measured using a pacemaker system analyser at a constant pulse width (0.6 msec.) and pacing rate.

MATERIAL & METHODS:
Forty studies of cardiac pacing threshold were done in 25 patients (18 males, 7 females) in the age range 24-80 years (mean age 59.5 Years) who were on temporary right ventricular endocardial pacemakers for the following indicat ions: Complete heart block (12), high grade atrio-ventricular block (8), and sick sinus syndrome (5). The results were subjected to statistical analysis using the student’s ‘t” test for paired data.

RESULTS:
GROUP 1: Nitroglycerine (Table I) - (Figure 1)

The group as a whole showed a significant decrease in the voltage and current threshold (p < 0.05). Though the changes in energy thres hold showed a decreasing trend, it did not achieve statistical significance. There was no significant change in the resistance of the lead.

DISCUSSION:

Excitation of a single myocardial cell or a syncitium of cells is a function dependent upon (1) the exciting stimulus, (ii) the resting membrane potential. The Pacemaker standard Subcommittee of the Association for the Advancement of Medical Instrumentation defines stimulat ion threshold as the “minimum stimulation level consistently producing propagated carcliac depolarization”. On the basis of this study, despite the limitations of an acute study, we conclude that the myocardial pacing threshold is not adversely affected by most of the anti-anginal agents. In fact, nitro-glycerine by decreasing the voltage and current thresholds and oxyfedrine by reducing the voltage threshold significantly, could prove to be useful in the setting of pacemaker exit blocks. The safety of verapamil and propranolol in this regard has previously been demonstrated by us.4