Postextrasystolic potentiation and echocardiography: the effect of varying basic heart rate, extrasystolic coupling interval and postextrasystolic interval.
Authors: M W Cooper, L O Lutherer, R M Lust
Journal: Circulation (1982)

The purpose of this study was to determine whether echocardiography can be used to monitor postextrasystolic potentiation (PESP) and, if so, which of the echocardiographic variables are valid indicators of PESP and under what conditions.An implantable M-mode echocardiographic transducer was sewn to the right ventricular outflow tract of the dog heart to record continuously across the minor diameter of the left ventricle.The sinus node pacemaking region was excised and a pacing protocol was used to vary the basic heart rate, the extrasystolic coupling interval and the postextrasystolic interval.The decreases in ejection time and diastolic dimension as well as the increases in the mean rate of circumferential fiber shortening (Vcf) and fractional shortening (%FS) that occur with increasing heart rate were detected by echocardiography.There were also increases in posterior wall maximal velocity and excursion and an increase in the rate of diastolic relaxation.Shortening the coupling interval of the extrasystole resulted in the expected potentiation of Vcf, %FS and the excursion, maximal velocity and rate of diastolic relaxation of the posterior wall.No correlation was observed for percent thickening of the posterior wall or interven- tricular septum, either because the technique was too insensitive or because wall thickening does not reflect the rapid-phase force-frequency perturbation of PESP.Allowing a full compensatory pause for the postex- trasystolic interval resulted in a greater potentiation of all variables than if the postextrasystolic interval was timed to occur when postextrasystolic diastolic pressure and dimension were identical to preextrasys- tolic diastolic pressure and dimension (isolength).However, only at isolength was potentiation highly predictable, and then only if the heart rate and the coupling interval were known.We conclude that most of the variables measured echocardiographically can be used to determine whether the PESP response is equivalent to a predicted value, provided all intervals are known or carefully controlled.THE POTENTIATION of contractile state after a sin- gle closely coupled extrasystole has been proposed as an index of the progression of regional contraction abnormalities in acutely ischemic cardiac muscle.' 2 Cohn et al.3 proposed echocardiography as a noninva- sive method of measuring the effects of externally induced postextrasystolic potentiation (PESP).We sought to determine whether echocardiography could be used to evaluate the PESP response experimentally and, if so, which echocardiographic variables are valid indicators of PESP and under what conditions. Methods Dog PreparationSeven adult mongrel dogs that weighed 20-30 kg were anesthetized with i.v.pentobarbital, 30 mg/kg, and underwent a tracheotomy.Cannulas were placed so their tips were in the aorta, the vena cava and the left ventricular (LV) and right ventricular (RV) chambers.The chest was opened by a thoracotomy at the right fourth intercostal space, and the dog was placed on positive-pressure ventilation for the remainder of the experiment.The heart was supported temporarily in a pericardial cradle.The sinus node pacemaker region was excised by a modification of the technique de- scribed by Euler et al.4An incision-resuture technique was applied to the entire sinoatrial nodal region to isolate the sinus pacemaker cells from the conduction