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The relationship between regional blood flow and contractile function in normal, ischemic, and reperfused myocardium
1Abteilung für Pathophysiologie Zentrum für Innere Medizin Universitätsklinikum Essen, Germany.
Insights
Myocardial blood flow and contractile function exhibit heterogeneity in the left ventricle. During ischemia, inner layers are more affected, with function recovery faster in outer layers post-reperfusion.
Area of Science:
- Cardiovascular Physiology
- Cardiac Mechanics
- Myocardial Perfusion
Background:
- Left ventricular function and blood flow are unevenly distributed.
- Heterogeneity exists both regionally (apex-base, anterior-posterior) and transmurally (inner vs. outer layers).
- Myocardial blood flow patterns are stable over several minutes.
Purpose of the Study:
- To investigate the relationship between myocardial blood flow and contractile function under normoperfusion, hypoperfusion, and reperfusion.
- To characterize the transmural and regional heterogeneity of myocardial function and flow.
- To examine the impact of ischemia duration and severity on the flow-function coupling.
Main Methods:
- Assessment of myocardial blood flow and segment shortening in the left ventricle.
- Analysis of transmural and regional variations in myocardial deformation and perfusion.
- Evaluation of flow-function coupling during normoperfusion, hypoperfusion, and reperfusion.
Main Results:
- Under normoperfusion, apex and anterior wall show greater shortening; inner myocardial layers exhibit greater shortening and blood flow.
- Hypoperfusion disproportionately affects subendocardial blood flow and inner layer function.
- During reperfusion, blood flow normalizes, but contractile function remains depressed, with faster recovery in outer layers.
Conclusions:
- Left ventricular function and perfusion are inherently heterogeneous.
- Ischemia preferentially impairs inner myocardial layers, and prolonged ischemia decouples flow from function.
- Reperfusion restores flow but recovery of function is layer-dependent and prolonged.
Abstract:
During normoperfusion, both myocardial blood flow and contractile function are heterogeneously distributed throughout the left ventricle, in that midwall segment shortening is higher at the apex than at the base of the left ventricle, and greater in the anterior than in the posterior wall. Also, transmural heterogeneity of myocardial deformation exists with greater segment shortening and wall thickening occurring in inner than in outer myocardial layers. A transmural heterogeneity of myocardial blood flow-with greater inner as compared to outer wall perfusion-exists which is not simply related to temporal fluctuations since the heterogeneous flow pattern is stable over at least a few minutes. 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 increase regional myocardial contractile function. During hypoperfusion, 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 in the outer myocardial layers. The reduced regional myocardial contractile function is closely matched to the reduced regional myocardial blood flow; however, such a coupling between reduced flow and function is lost when ischemia is prolonged for several hours in that function for a given flow is further reduced. 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 to almost normal. Recovery of contractile function in the outer myocardial layers is faster than in the inner myocardial layers.