How do ACEI / ARB work in HFrEF and MI but produce “no benefit” in HFpEF?
When the heart is failing, it doesn’t pump as effectively. Opening the blood vessels and lowering blood pressure are important because that reduces how hard the heart needs to work. It may help keep blood from backing up in the heart and lungs.
Mechanism 1: Systemic Vasodilation. ACE inhibitors are vasodilators; that means they dilate systemic blood vessels and thus help improve blood flow. This decreases the amount of work the heart has to do. ACEIs work by blocking the production of angiotensin II (a potent vasoconstrictor) whose production is increased as a result of heart failure. When the heart is failing and not pumping well, angiotensin II is released to constrict the vessels to maintain enough blood pressure to perfuse vital organs. [KTA]. Angiotensin II is one of the most potent vasoconstrictors in the body.
Mechanism 2: Sodium and water excretion. ACEIs also lower the amount of salt (sodium) and water in your body, which also helps to lower your blood pressure.
ACEIs also used to control high blood pressure, prevent kidney damage from diabetes (b/c they are renoprotective), and prevent more heart damage after a heart attack.
ACE inhibitors are critical in the treatment of heart failure when systolic dysfunction is present and may also be prescribed for the treatment of diastolic dysfunction.
Why are ACEIs used for heart failure?
“They relieve heart failure symptoms, such as fluid buildup and swelling, and help you feel better. They may help you live longer and stay out of the hospital. You may need to take an ACE inhibitor if you have recently had a heart attack. This is true even if you do not have symptoms of heart failure.”
Reference
https://www.cardiosmart.org/~/media/Documents/Fact%20Sheets/en/zp3950.ashx (American College of Cardiology)