From the Guidelines
Afterload in the heart refers to the pressure or resistance that the ventricles must overcome to eject blood during contraction, with the right ventricle's afterload being most appropriately defined as the RV wall stress during systolic ejection estimated by the summation of the resistive and pulsatile components of blood flow. This concept is crucial in understanding cardiac performance and energy requirements, as increased afterload can lead to decreased cardiac output, increased myocardial oxygen demand, and eventual heart failure if sustained 1.
Key Points About Afterload
- Afterload is a primary determinant of normal RV function, and RVEF is inversely proportional to pulmonary artery (PA) pressure (PAP) 1.
- The RV has a shallower end-systolic PV slope than the LV, which results in lesser change in end-systolic pressure, generating greater change in end-systolic volume, making RV systolic function highly sensitive to changes in afterload 1.
- Commonly used measures of RV afterload, including PA systolic pressure (PASP) and pulmonary vascular resistance (PVR), provide an inadequate description of RV afterload because they do not account for contributions of pulsatile loading 1.
- Elevated left-sided heart (LH) disease filling pressures directly increase RV afterload, secondarily reduce PA compliance, and increase PA resistance through acute vasoconstriction and chronic vascular remodeling 1.
Clinical Implications
- Understanding afterload is crucial for managing various cardiovascular conditions as it directly impacts cardiac performance and energy requirements.
- Medications that reduce afterload, such as vasodilators, are commonly used to treat conditions with elevated afterload, helping to decrease the workload on the heart and improve cardiac efficiency.
- The optimal mechanical coupling of RV function to afterload corresponds to a ratio of Ees to arterial elastance of 1.0, with uncoupling occurring below a ratio of 0.6 to 1.0, which is important for maintaining efficient RV function 1.
From the FDA Drug Label
Amlodipine reduces the total peripheral resistance (afterload) against which the heart works The afterload in the heart is the total peripheral resistance against which the heart works. In other words, it is the pressure that the heart must overcome to eject blood into the circulation.
- Afterload is an important determinant of cardiac function, as it affects the amount of blood that the heart can pump with each beat.
- Reduction in afterload can lead to an increase in cardiac output, as the heart does not have to work as hard to eject blood into the circulation 2.
From the Research
Definition of Afterload
- Afterload refers to the resistance or "load" that the heart must overcome to eject blood into the systemic circulation during systole 3.
- It is defined as all of the factors that contribute to total myocardial wall stress (or tension) during systolic ejection 3.
Factors Affecting Afterload
- Afterload is influenced by several factors, including systemic vascular resistance, aortic pressure, and impedance 4, 5.
- It is also affected by the interdependence of preload and afterload, as well as the presence of atrioventricular valve regurgitation 5.
Effects of Afterload Reduction
- Reduction of afterload has been shown to produce substantial hemodynamic benefits in patients with heart failure, including reduced filling pressures and increased forward cardiac output 4.
- Afterload reduction can be achieved through the use of vasodilator drugs, which can improve cardiac function and reduce symptoms in patients with heart failure 4, 5.
- However, the effects of afterload reduction can vary depending on the specific context and the presence of other factors, such as regional ischemia 6, 7.