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Decreased myocardial oxygen consumption indices in dynamic cardiomyoplasty
F Y Chen1, B J deGuzman, L Aklog
1Division of Applied Sciences, Harvard Graduate School of the Arts and Sciences, Cambridge, Mass, USA.
Insights
Dynamic cardiomyoplasty with a fluid-filled balloon reduces myocardial oxygen consumption (MVo2). Optimizing latissimus dorsi stimulation parameters significantly enhances this MVo2 reduction, improving the benefits of this cardiac procedure.
Area of Science:
- Cardiovascular Surgery
- Biomedical Engineering
- Cardiac Physiology
Background:
- Previous studies on dynamic cardiomyoplasty (DCM) inaccurately calculated myocardial oxygen consumption (MVo2) by not accounting for the altered epicardial reference pressure.
- In DCM, the latissimus dorsi (LD) muscle generates compressive pressure, changing the epicardial pressure from atmospheric to a higher value.
Purpose of the Study:
- To accurately investigate the theory of decreased MVo2 in DCM.
- To calculate MVo2 indices using transmural myocardial pressure (Pt) in DCM, accounting for the LD muscle's contribution.
Main Methods:
- A fluid-filled balloon was placed between the LD and myocardium in a balloon-mediated cardiomyoplasty model in goats.
- Transmural myocardial pressure (Pt) was calculated as left ventricular pressure minus balloon luminal pressure.
- Indices of MVo2, including transmural tension time index (TtTI) and transmural pressure volume area (PtVA), were calculated using Pt.
Main Results:
- With standard LD stimulation, TtTI decreased by 48% and PtVA by 21% upon LD contraction.
- Optimized LD stimulation parameters resulted in a 45% decrease in TtTI and a 33% decrease in PtVA.
- These findings demonstrate a significant reduction in MVo2 indices with DCM and optimized LD stimulation.
Conclusions:
- Dynamic cardiomyoplasty utilizing a fluid-filled balloon effectively decreases MVo2 during LD contraction.
- The effectiveness of MVo2 reduction in DCM is significantly influenced by the chosen LD stimulation parameters.
Background:
To investigate the theory of decreased myocardial oxygen consumption (MVo2) in dynamic cardiomyoplasty (DCM), previous studies have calculated indices of MVo2 in DCM. These previous studies, however, used left ventricular pressure in formulas that assumed the assumed the heart to be in its native state, with the reference pressure at the epicardium assumed to be atmospheric. In DCM, however, the reference pressure at the epicardium is no longer atmospheric but rather is the compressive pressure generated by the latissimus dorsi (LD). We therefore used the transmural myocardial pressure, Pt, to calculate indices of MVo2 in DCM.
Methods And Results:
A half-ellipsoidal, fluid-filled balloon was interposed between the LD and myocardium in a balloon-mediated cardiomyoplasty procedure in five goats. With commonly used LD stimulation parameters, Pt was calculated as left ventricular pressure minus balloon luminal pressure. Using Pt, the transmural tension time index (TtTI) and transmural pressure volume area (PtVA) were calculated. In another series of four goats, LD stimulation parameters were optimized and the TtTI and PtVA recalculated. With standard LD stimulation parameters, the TtTI decreased by 48%, from 15.8 to 8.2 mm Hg.s, and the PtVA by 21%, from 775 to 612 mm Hg.mL, as the LD was stimulated to contract. When the optimized parameters were used, the TtTI decreased by 45%, from 11.2 to 6.2 mm Hg.s, and the PtVA by 33%, from 1984 to 1371 mm Hg.mL.
Conclusions:
Our results suggest that DCM with a fluid-filled balloon decreases MVo2 as the LD contracts and that LD stimulation parameters have a determining effect on this benefit.