Key Points
- To determine the coupling between regional myocardial segment work and local oxygen consumption, and assess how tachycardia-induced regional work changes affect external cardiac work.
- Paced open-chest anesthetized dogs at heart rates from 120 to 270 beats/min while measuring global hemodynamics and coronary sinus flow.
- Quantified regional segment work via ultrasonic dimension crystals and strain gauge arches, regional blood flow via radioactive microspheres, and oxygen saturation via microspectrophotometry.
- Measured mitochondrial NADH redox levels continuously using surface fluorometry.
- Increasing heart rate from 120 to 180 beats/min increased regional work from 3040 (SEM 220) to a peak of 4290 (280) mm·g⁻¹·min⁻¹ and regional oxygen consumption from 6.16 (0.47) to 8.29 (0.53) ml O2·min⁻¹·100 g⁻¹ (linear correlation r = 0.971, p < 0.05).
- External cardiac work did not increase with initial pacing [67.0 (2.6) to 65.3 (4.4) mm Hg·L⁻¹·min⁻¹] and decreased overall by ~26% at higher rates, while global myocardial oxygen consumption increased by 49% and NADH redox levels rose by up to 67%.
Structured PICO
PPopulationOpen chest anaesthetised dogs
IInterventionPacing at frequencies of 120-270 beats.min-1 to induce tachycardia
CComparatorBaseline heart rate (120 beats.min-1)
OOutcomeRelationship between regional myocardial segment work and regional oxygen consumption, and changes in external cardiac worksurrogate
Myocardial oxygen consumption is more closely related to regional segment work than to external work, and tachycardia significantly raises the oxygen cost of external cardiac work.