From the Guidelines
Changes in myocardial contractility shift the Frank-Starling curve upward or downward while maintaining its characteristic shape, with increased contractility shifting the curve upward and decreased contractility shifting it downward. This concept is crucial in understanding how the heart adapts to various conditions, including those that affect myocardial contractility. When contractility increases (positive inotropy), the Frank-Starling curve shifts upward, meaning the heart generates more stroke volume and cardiac output at any given preload or end-diastolic volume. This allows the heart to pump more blood with the same filling pressure. Conversely, decreased contractility (negative inotropy) shifts the curve downward, resulting in less stroke volume at the same preload.
Factors Affecting Contractility
Factors that increase contractility include:
- Sympathetic stimulation
- Catecholamines like epinephrine and norepinephrine
- Medications such as dobutamine, milrinone, and digoxin On the other hand, factors decreasing contractility include:
- Hypoxia
- Acidosis
- Beta-blockers
- Certain disease states like heart failure or cardiomyopathy
Physiological Basis
The physiological basis for these shifts relates to calcium handling within cardiomyocytes - increased contractility typically involves enhanced calcium entry into cells or improved calcium sensitivity of myofilaments, allowing for stronger cross-bridge formation between actin and myosin, as discussed in the context of cardiac hypertrophy and remodeling 1. Understanding these shifts is crucial in clinical settings when managing patients with heart failure, as interventions often aim to optimize contractility to improve cardiac performance.
Clinical Implications
In the context of valvular heart disease, such as aortic regurgitation, the management of patients involves considering the impact of changes in myocardial contractility on the Frank-Starling curve, as outlined in guidelines for the management of patients with valvular heart disease 1. The goal is to maintain optimal cardiac function and prevent the progression to heart failure, where possible. This may involve the use of vasodilator therapy to reduce the hemodynamic burden on the heart, as well as other interventions aimed at optimizing contractility and improving cardiac performance.
From the Research
Effect of Changes in Myocardial Contractility on the Frank-Starling Curve
- The Frank-Starling curve describes the relationship between the stroke volume of the heart and the end-diastolic volume, which is a measure of the heart's preload 2, 3.
- Changes in myocardial contractility can shift the Frank-Starling curve, with increased contractility resulting in a upward shift and decreased contractility resulting in a downward shift 4, 5.
- The use of inotropic agents, such as dobutamine, can increase myocardial contractility and shift the Frank-Starling curve upward, resulting in increased cardiac output 3.
- However, the effects of changes in myocardial contractility on the Frank-Starling curve can be complex and depend on various factors, including the underlying cardiac function and the presence of other cardiovascular diseases 6.
- The force-frequency relation (FFR) is a measure of the relationship between heart rate and contractility, and can be used to assess the contractile reserve of the heart 5.
- Measurements of FFR can be used to diagnose latent contractile dysfunction and residual contractile reserve in patients with heart failure, and can provide prognostic information beyond traditional measures of cardiac function 5.