title: Systolic time intervals in measurement of inotropic response to drugs.
abstract: During periods of tachycardia induced by atrial pacing in eight patients, moderate increments in dP/dt(max) and (dP/dt)/CPIP (common produced intraventricular pressure) and moderate reductions in left ventricular ejection time (LVET) and Q-S2 were demonstrated. These changes varied between individuals, but reduction in systolic intervals was consistently less than that reported from populations showing a range of resting heart rates. Individual regression formulae relating each variable to paced heart rate were used to calculate rate-dependent and rate-independent changes induced by isoprenaline and ouabain. Despite technical difficulty in precise measurement of systolic intervals, there was an excellent inverse correlation between rate-independent changes in Q-S2 and in both dP/dt(mac) and (dP/dt)/CPIP. Rate-independent change in Q-S2 appears to be a practical, moderately sensitive, and reasonably precise measure of the inotropic effect of a drug which does not radically alter left ventricular end-diastolic pressure or blood pressure. Day-to-day variation in systolic intervals may limit the use of the technique to studies of short duration.
mesh_terms: D000328:Adult; D002316:Cardiotonic Agents / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006352:Heart Ventricles / Q000187:drug effects; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D013599:Systole / Q000187:drug effects
chemical_list: D002316:Cardiotonic Agents; D010042:Ouabain; D007545:Isoproterenol