Ventricular postextrasystolic potentiation in the dog. A study using list mode radionuclide ventriculography.

The first and second postextrasystolic sinus beats (PESB) were isolated and analyzed in five open-chested dogs with the aid of list mode radionuclide ventriculography. Ventricular stimulation was delivered using a coupling interval of 150 msec from electrodes positioned at two (in two animals) or five (in three animals) different ventricular sites. There were marked increases in both left ventricular ejection fraction (41.5 +/- 4% vs. 56.8 +/- 3.9%; control vs. PESB, p less than 0.001) and stroke volume (+ 51.6 +/- 16.8%; PESB vs. control, p less than 0.001) in all first postextrasystolic sinus beats. Concomitant decreases in end-systolic volumes (-16.2 +/- 5.2%; PESB vs. control beat, p less than 0.001) confirmed the increased inotropy seen during these beats. During the second postextrasystolic sinus beats a mild but statistically significant increase in ejection fraction (+ 1.6 +/- 1.6%; PESB vs., control, p less than 0.01) was also seen despite a small decrease in end-diastolic volume (-2.8 +/- 2.5%; PESB vs control, p less than 0.01). In the dog postextrasystolic potentiation affects mostly the first PESB and causes only a mild increase in inotropy during the subsequent sinus beat. List mode radionuclide ventriculography is a useful and reproducible method for assessing changes in ventricular function following ventricular ectopics that have a fixed coupling interval to the preceding QRS complex.