From the Guidelines
Mitral regurgitation (MR) decreases afterload.
Rationale
- In MR, the left ventricle (LV) ejects blood into the left atrium (LA) during systole, which reduces the impedance to LV ejection, thereby decreasing afterload 1.
- This decrease in afterload is due to the unloading of the LV into the LA, allowing for a larger total stroke volume and a normal forward stroke volume 1.
- The reduced afterload in MR is a compensatory mechanism that facilitates LV ejection and maintains forward cardiac output, even in the presence of significant regurgitation 1.
- However, it is essential to note that while MR decreases afterload, it also increases preload due to the volume overload caused by the regurgitant flow 1.
- The management of MR involves correcting the valvular lesion before the onset of LV systolic dysfunction, and medical therapy may include beta-adrenergic blockade, ACE inhibitors, and aldosterone antagonists to reduce the burden of volume overload and prevent LV dysfunction 1.
From the Research
Mitral Regurgitation and Afterload
- Mitral regurgitation (MR) is generally believed to create a systolic 'unloading' effect by providing a low-resistance ejection into the left atrium, which is thought to increase the left ventricular ejection fraction (EF) and mask a reduced contractile state 2.
- However, studies have shown that chronic MR is not associated with an unloading effect, and calculated values for circumferential and meridional wall stress were found to be normal or high in patients with chronic MR 2.
- In decompensated MR, systolic wall stress tends to increase after mitral valve replacement (MVR), which can contribute to a postoperative decline in myocardial fibre shortening and a lower EF 2.
- By contrast, patients with compensated MR exhibit a decline in systolic wall stress after MVR, despite this postoperative decline in afterload, fibre shortening falls 2.
- The easy unloading of the left ventricle via both aortic and mitral valves during systole is the hallmark of chronic mitral regurgitation, and the volume overload in mitral regurgitation leads to eccentric hypertrophy of the left ventricle while the mass-to-volume quotient remains within normal limits 3.
- The myocardial wall stress of the left ventricle at the end of systole is reduced in mitral regurgitation, and even in the presence of substantially reduced contractility, the left ventricular function appears adequate 3.
Effects of Afterload Reduction on Mitral Regurgitation
- Afterload reduction with vasodilators and diuretics decreases mitral regurgitation during upright exercise in advanced heart failure 4.
- Intensive reduction of ventricular filling pressure and systemic vascular resistance decreases total ventricular stroke volume but increases forward stroke volume 5.
- Tailored afterload reduction decreases mitral regurgitation at rest and during upright exercise, and increases the forward ejection fraction without changing total ejection fraction 4.
- Afterload reduction may halt the progression of left ventricular dysfunction in patients with chronic compensated mitral regurgitation, while beta-adrenergic blockade may worsen progression of left ventricular dysfunction 6.