title: Paired pulse pacing increases cardiac O2 consumption for activation without changing efficiency of contractile machinery in canine left ventricle.
abstract: The relation between cardiac O2 consumption (VO2) and the total mechanical energy (TME) generated by contraction was studied under paired-pulse (PP) pacing and compared with that under single-pulse pacing at the same basic rate as PP pacing and at the double-pacing rate in ten excised cross-circulated canine left ventricles (LV). TME was assessed by the systolic pressure-volume (P-V) area (PVA) defined as the area bounded by the end-systolic and end-diastolic P-V curves and the systolic P-V trajectory. The VO2-PVA relation was linear under PP pacing as well as at control and double heart rates. PP pacing increased LV contractility index Emax from 6.3 +/- 3.3 (SD) to 18.0 +/- 8.6 mmHg/(ml/100 g) and elevated markedly the VO2-PVA relation by increasing the VO2-axis intercept (or PVA-independent VO2) from 0.62 +/- 0.11 to 1.13 +/- 0.35 J.beat-1.100 g-1. However, PP pacing did not change the slope of the VO2-PVA relation at 2.24 +/- 0.53 (dimensionless). The efficiency from PVA-dependent VO2 (total VO2-PVA-independent VO2) to PVA (=TME), calculated as the reciprocal of the slope of the VO2-PVA relation, was also constant at 47 +/- 11% regardless of PP pacing. These results are similar to previous results obtained by positive inotropic interventions with catecholamines and Ca2+. We conclude that PP pacing augments the PVA-independent VO2 for activation without affecting the efficiency of the contractile machinery to generate TME from the PVA-dependent VO2.
authors.affiliation: Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Suita, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Suga
authors.forename: S
authors.initials: S
authors.lastname: Futaki
authors.forename: N
authors.initials: N
authors.lastname: Tanaka
authors.forename: Y
authors.initials: Y
authors.lastname: Yasumura
authors.forename: T
authors.initials: T
authors.lastname: Nozawa
authors.forename: D
authors.initials: D
authors.lastname: Wu
authors.forename: Y
authors.initials: Y
authors.lastname: Ohgoshi
authors.forename: H
authors.initials: H
authors.lastname: Yaku
mesh_terms: D000818:Animals; D002304:Cardiac Pacing, Artificial / Q000379:methods; D004285:Dogs; D004562:Electrocardiography; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D009200:Myocardial Contraction; D010101:Oxygen Consumption; D016276:Ventricular Function