Systolic Compression of Coronary Vessels

Systolic Compression of Coronary Vessels is the mechanical narrowing and impedance of blood flow through the small intramural coronary vessels that occurs during ventricular contraction, resulting from the pressure generated by the surrounding contracting myocardium acting directly on the embedded vasculature.

Mechanism of Compression

Intramyocardial Pressure Generation

As the ventricular wall contracts during systole, tension develops within the myocardium that generates substantial intramyocardial pressure, particularly in the inner layers of the wall, and this pressure is transmitted directly to the small coronary vessels coursing through the muscle, narrowing their lumen and increasing resistance to flow.

Transmural Gradient of Compression

The magnitude of systolic compression is not uniform across the thickness of the ventricular wall, being greatest in the subendocardial layer, where intramyocardial pressure most closely approaches or can even exceed ventricular cavity pressure, and progressively diminishing toward the subepicardial layer, which experiences comparatively less compressive force.

Functional Consequences

Impedance to Left Ventricular Flow

Because the left ventricle generates high systolic pressure and possesses a thick muscular wall, systolic compression substantially impedes coronary flow to the left ventricular myocardium during this phase, contributing to the diastolic dominance characteristic of left coronary circulation.

Relative Sparing of Right Ventricular Flow

The right ventricle, generating much lower systolic pressure, produces correspondingly less intramyocardial compression, allowing right coronary flow to continue more substantially throughout systole compared to the pattern observed on the left side.

Determinants of Compression Severity

Ventricular Wall Tension

Greater ventricular wall tension during systole, influenced by factors such as ventricular pressure, chamber radius, and wall thickness according to relationships analogous to the law of Laplace, produces greater intramyocardial pressure and correspondingly more severe compression of the embedded coronary vessels.

Duration of Systole

The proportion of the cardiac cycle spent under compressive conditions depends on the relative duration of systole, meaning that changes in heart rate and contractile timing influence the overall fraction of time during which coronary vessels are subject to this compressive effect.

Clinical and Pathophysiological Relevance

Vulnerability of Hypertrophied Myocardium

In conditions such as ventricular hypertrophy, increased wall thickness and elevated intraventricular pressure can intensify systolic compression, further reducing the proportion of the cardiac cycle during which adequate coronary perfusion is possible and increasing the vulnerability of the myocardium, particularly the subendocardium, to ischemia.

Interaction with Coronary Artery Disease

In the presence of an already narrowed coronary artery due to atherosclerotic disease, the additional resistance imposed by systolic compression can further limit flow during systole, compounding the reduction in coronary flow reserve and increasing the likelihood of ischemia during periods of increased myocardial oxygen demand.

Physiological Significance

Explaining the Timing of Myocardial Perfusion

Systolic compression of coronary vessels provides the fundamental mechanical explanation for why myocardial perfusion, particularly to the left ventricle, is concentrated in diastole, establishing a direct link between the mechanics of cardiac contraction and the physiological pattern of the heart's own blood supply.