Stimulation threshold of myocardial electrodes in long-term cardiac pacing.

The stimulation threshold behaviour in long-term cardiac pacing is presented for a material of 45 myocardial electrodes. The initial stimulation threshold was measured in 25 cases and the mean value was 1.5 +/- 0.7 mA. The follow-up period was from 17 to 99 months (mean 50 months) and during that time 63 threshold measurements were made. The mean chronic stimulation threshold was 2.2 +/- 0.7 mA. It was not dependent on the aetiology or type of the conduction defect. There was no relationship between the initial and chronic stimulation threshold. In the region of the left ventricular apex, the chronic stimulation threshold was higher than in the anterior wall of the right ventricle. The long-term stimulation threshold was significantly higher in the cases of enlarged heart and in the age group less than or equal to 50 years than in those with a heart of normal size and in the age group greater than or equal to 70 years.