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Coronary vascular resistance increases under full bypass support of centrifugal pumps--relation between myocardial
Masahiko Ando1, Yoshiaki Takewa, Takashi Nishimura
1Department of Artificial Organs, National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan. masandoo@hotmail.com
Insights
Left ventricular assist device support can decrease coronary flow (CoF) and myocardial oxygen consumption (MVO2). Studies show increased coronary vascular resistance (CVR) with 100% bypass, possibly due to pump mechanics or autoregulation.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Medical Devices
Background:
- Coronary circulation is intrinsically linked to myocardial oxygen consumption (MVO2).
- Previous research indicates a potential decrease in coronary flow (CoF) during left ventricular assist device (LVAD) support.
- The autoregulatory mechanisms maintaining optimal CoF relative to MVO2 under LVAD support require further elucidation.
Purpose of the Study:
- To investigate the impact of centrifugal pumps on coronary flow (CoF).
- To assess the relationship between bypass rates, left ventricle workload, and coronary circulation.
- To evaluate changes in myocardial oxygen consumption (MVO2) and coronary vascular resistance (CVR) under varying LVAD support levels.
Main Methods:
- Utilized an adult goat model (n=10) with an EVAHEART centrifugal pump.
- Experimentally set three conditions: Circuit-Clamp (no support), 50% bypass, and 100% bypass.
- Measured coronary flow (CoF), myocardial oxygen consumption (MVO2), pressure-volume area (PVA), and coronary vascular resistance (CVR) across all conditions.
Main Results:
- Under 100% bypass, significant decreases in CoF, MVO2, and PVA were observed compared to the clamp condition.
- In 50% bypass, CoF and MVO2 decreased from clamp, but PVA remained unchanged.
- A notable 40% increase in CVR was recorded at 100% bypass, suggesting potential mechanical collapse or autoregulatory vasoconstriction.
Conclusions:
- LVAD support, particularly at high bypass rates, can alter coronary hemodynamics and increase CVR.
- The observed increase in CVR may stem from mechanical effects of the pump or an autoregulatory response.
- Clinical optimization of LVAD speed is crucial to prevent adverse coronary vascular events like collapse; further research in heart failure models is warranted.
Abstract:
Coronary circulation is closely linked to myocardial oxygen consumption (MVO(2)), and previous reports have suggested decreased coronary flow (CoF) under left ventricular assist device support. Decreased CoF itself under support is not unfavorable because the native heart can be well unloaded and myocardial oxygen demand is also decreased. There should be an autoregulatory system that would maintain optimal CoF according to oxygen demand; however, the detailed mechanism is still unclear. The aim of the current study is to evaluate the effect of centrifugal pumps on CoF under varied bypass rates in relation to left ventricle workload. A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed in an adult goat (n = 10, 61.3 ± 6.5 kg). We set up the following conditions, including Circuit-Clamp (i.e., no pump support), 50% bypass, and 100% bypass. In these settings, CoF, MVO(2), pressure-volume area (PVA), and coronary vascular resistance (CVR) were measured. In 100% bypass, CoF, MVO(2), and PVA were all decreased significantly from clamp. While in 50% bypass, CoF and MVO(2) decreased from clamp, but not PVA. There was a significant 40% increase in CVR in 100% bypass from clamp. This CVR increase in 100% bypass was possibly due to mechanical collapse of coronary vascular bed itself by pump support or increased vascular tone through autoregulatory system. In clinical settings, we should adjust optimal pump speed so as not to cause this vascular collapse. However, to clarify autoregulatory system of the coronary perfusion, further investigation is ongoing in ischemic and heart failure models.
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