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Balance and imbalance of regional myocardial contractile function and blood flow
1Abteilung für Pathophysiologie, Zentrum für Innere Medizin, Universitätsklinikum Essen, Hufelandstrasse 55, 45122 Essen, Germany.
Insights
Myocardial blood flow and contractile function are unevenly distributed in the left ventricle. During ischemia, reduced blood flow severely impacts function, especially in inner heart layers.
Area of Science:
- Cardiovascular Physiology
- Myocardial Mechanics
- Coronary Circulation
Background:
- Left ventricular function and blood flow exhibit significant heterogeneity, both regionally and transmurally, during normal perfusion.
- Understanding these heterogeneities is crucial for diagnosing and treating various cardiac conditions.
Purpose of the Study:
- To investigate the relationship between myocardial blood flow and contractile function under normal and ischemic conditions.
- To characterize the spatial distribution of mechanical function and perfusion within the left ventricle.
Main Methods:
- The study likely involved advanced imaging techniques to assess myocardial deformation and blood flow.
- Experimental models were used to induce and study conditions like hypoperfusion and embolization.
Main Results:
- Heterogeneous distribution of segment shortening and wall thickening observed, with greater function in the apex and anterior wall, and inner myocardial layers.
- Myocardial blood flow is also greater in inner than outer layers.
- During hypoperfusion, subendocardial flow and function decline more rapidly than subepicardial.
- Perfusion-contraction mismatch occurs during acute microcirculation embolization.
- Post-ischemia, contractile function recovery is prolonged despite restored blood flow.
Conclusions:
- Regional disparities in myocardial perfusion and function are significant in the left ventricle.
- Ischemia disproportionately affects subendocardial layers, leading to rapid functional loss.
- The coupling between blood flow and function can be disrupted during prolonged ischemia and reperfusion.
Abstract:
During normoperfusion, both contractile function and myocardial blood flow are heterogeneously distributed throughout the left ventricle. Midwall segment shortening is greater at the apex than at the base of the left ventricle, and it is greater in the anterior than in the posterior wall. Also, transmural heterogeneity of myocardial deformation exists, with greater segment shortening and wall thickening in inner than in outer myocardial layers. Myocardial blood flow is greater in inner than in outer myocardial layers. Apart from transmural heterogeneities, there are adjacent regions with largely different resting flow in the same heart. While an increase in myocardial contractile function will lead to a metabolically mediated increase in myocardial blood flow, an increase in regional coronary perfusion within or above the autoregulatory range does not, in turn, increase regional myocardial contractile function. During hypoperfusion induced by a proximal coronary stenosis, the reduction in subendocardial blood flow is more pronounced than that in subepicardial blood flow, and contractile function in the inner myocardial layers ceases more rapidly than that in outer myocardial layers. The reduced regional myocardial contractile function is closely matched to the reduced regional myocardial blood flow; however, such coupling between reduced flow and function is lost when ischemia is prolonged for several hours, i.e., function for a given flow is further reduced. Acute embolization of the coronary microcirculation induces a progressive loss of regional myocardial function at unchanged regional myocardial blood flow, i.e., perfusion-contraction mismatch. During reperfusion, regional myocardial contractile function remains depressed for a prolonged period of time, depending on the severity, duration and location of the preceding ischemic episode, while regional myocardial blood flow is restored.