# Paired pulse pacing increases cardiac O_{2} consumption for activation without changing efficiency of contractile machinery in canine left ventricle

## Summary

The relation between cardiac O_{2} consumption (Vo_{2}) 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 Vo_{2}-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 Vo_{2}-PVA relation by increasing the Vo_{2}-axis intercept (or PVA-independent Vo_{2}) 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 Vo_{2}-PVA relation at 2.24±0.53 (dimensionless). The efficiency from PVA-dependent Vo_{2} (total Vo_{2}-PVA-independent Vo_{2}) to PVA (= TME), calculated as the reciprocal of the slope of the Vo_{2}-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 Ca^{2+}. We conclude that PP pacing augments the PVA-independent Vo_{2} for activation without affecting the efficiency of the contractile machinery to generate TME from the PVA-dependent Vo_{2}.

## Key words

Heart Cardiac energetics Pressure-volume area Excitation-contraction coupling Efficiency## Preview

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## References

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