ACE Inhibitor (Angiotensin-Converting Enzyme Inhibitor) [ACE]

An ACE inhibitor (angiotensin-converting enzyme inhibitor) is a class of medication that lowers blood pressure and reduces the workload on the heart by blocking the enzyme that converts angiotensin I into angiotensin II. Angiotensin II is a powerful vasoconstrictor: it narrows blood vessels and stimulates the release of aldosterone, a hormone that causes the kidneys to retain sodium and water, raising blood pressure. By blocking this conversion, ACE inhibitors cause blood vessels to relax and dilate, reducing both blood pressure and the resistance against which the heart must pump.

ACE inhibitors are among the most widely used and evidence-based medications in cardiology. They are a first-line treatment for heart failure with reduced ejection fraction (HFrEF), where they have been shown to reduce mortality and hospitalisations. They are also prescribed after heart attack, particularly when the left ventricular function is impaired, to limit further remodelling of the damaged heart muscle. In people with hypertension, diabetes, or chronic kidney disease, ACE inhibitors provide both blood pressure control and additional organ protection.

For survivors of sudden cardiac arrest who are found to have impaired left ventricular function, an ACE inhibitor is typically a core part of the medication regimen. The dose is usually started low and increased gradually (up-titrated) under the supervision of the cardiology team. Common side effects include a persistent dry cough, which affects around 10 to 15 percent of patients and is caused by a build-up of bradykinin. If the cough is troublesome, an angiotensin receptor blocker (ARB) such as candesartan or valsartan provides equivalent benefits without this side effect.

Less common but more serious side effects include angio-oedema (swelling of the lips, tongue or throat, requiring immediate medical attention), raised potassium levels (hyperkalaemia) and a fall in kidney function, particularly when starting treatment or after dose increases. Regular blood tests to monitor kidney function and potassium are standard practice, especially in the first few months and after any dose change.