From the Guidelines
The largest contributor to afterload is systemic vascular resistance (SVR), which is significantly influenced by hypertension, a major risk factor for aortic stenosis (AS) and associated with increased rate of progression and reduced survival 1.
Factors Influencing Afterload
Afterload represents the pressure that the ventricle must overcome to eject blood during contraction. Several factors contribute to afterload, but SVR is the primary determinant of this pressure in the systemic circulation.
- SVR is influenced by blood vessel diameter, blood viscosity, and total vessel length.
- Vasoconstriction increases SVR and thus afterload, while vasodilation decreases it.
- Other contributors to afterload include aortic valve stenosis, which creates resistance to ventricular ejection, and aortic compliance, which affects the pressure wave reflection back to the heart.
Clinical Management of Afterload
Clinically, afterload can be manipulated using medications to reduce SVR and thus decrease afterload, which is particularly important in managing conditions like heart failure or hypertension.
- Vasodilators (such as nitroprusside, hydralazine, or ACE inhibitors) can be used to reduce SVR and decrease afterload.
- The treatment of hypertension is a valid target in reducing afterload, with recommended systolic blood pressure targets of 130–139 mmHg and diastolic blood pressure targets of 70–90 mmHg 1.
- Studies, such as the Symptomatic Cardiac Obstruction-Pilot Study of Enalapril in Aortic Stenosis (SCOPE-AS), have shown that gradual titration of enalapril can be well tolerated in patients with symptomatic severe AS, no syncope or hypotension, and preserved LV systolic function 1.
From the FDA Drug Label
Amlodipine reduces the total peripheral resistance (afterload) against which the heart works The largest contributor to afterload is total peripheral resistance. 2
- Afterload is the pressure against which the heart must work to eject blood into the circulation.
- Total peripheral resistance is the resistance to blood flow in the systemic circulation, which is the main determinant of afterload.
From the Research
Largest Contributor to Afterload
The largest contributor to afterload is related to the systemic vascular resistance, which is influenced by various factors such as hypertension, diabetes, obesity, active smoking, hypercholesterolemia, and inactivity 3.
- Systemic vascular resistance index (SVR(i)) is a measure of afterload that takes into account central venous pressure (CVP), cardiac index (C(i)), and mean arterial blood pressure (MAP) 4.
- Total systemic vascular resistance index (TSVR(i)) is another measure of afterload that ignores the contribution of CVP, but has been shown to have a high degree of correlation with SVR(i) 4.
- The renin-angiotensin-aldosterone system plays an important role in regulating blood pressure and body volume, and ACE inhibitors can reduce afterload by preventing ventricular remodeling and retarding atherogenic changes in the vessel walls 3.
Factors Influencing Afterload
Several factors can influence afterload, including:
- Arterial elastance (Ea) 5
- Total arterial compliance (Ca) 5
- Systemic vascular resistance index 5
- Cardiac performance and vascular effects, as measured by afterload-related cardiac performance (ACP) 6
- Vasodilator drugs, which can reduce ventricular afterload and produce substantial hemodynamic benefit in patients with heart failure 7
Clinical Significance of Afterload
Afterload is an important factor in influencing cardiac function, particularly in patients with heart failure 7. Elevated arterial afterload has been identified as a contributor to the hemodynamic presentation in patients with low gradient severe aortic stenosis and preserved ejection fraction 5. Afterload-related cardiac performance (ACP) has been shown to be a powerful independent hemodynamic predictor of mortality in patients with chronic heart failure 6.