ACE Inhibitors in the Treatment of Congestive Heart Failure
Angiotensin Converting Enzyme (ACE) Inhibitors are one of the drugs used to treat Congestive Heart Failure (CHF). They work by increasing vasodilation and decreasing workload of the heart in patients with CHF.
Mode of Action
ACE inhibitors prevent vasoconstriction by suppressing the angiotensin converting enzyme, preventing angiotensin I from converting into angiotensin II. Angiotensin converting enzyme is responsible for converting angiotensin I to angiotensin II which is responsible for vasoconstriction. In addition to being a powerful vasoconstrictor, Angiotensin II is also responsible for hypertrophy of vascular tissues and aldosterone secretion. Hypertrophy of vascular tissues causes vessels to become narrow resulting in increased workload on the heart. Aldosterone secretion is primarily responsible for water retention which can increase vascular fluid volume also increasing the workload on the heart. Therefore, the inhibition of angiotensin II decreases the amount of pressure in the heart which decreases workload on the heart. Another beneficial effect of ACE inhibitors is that they increase bradykinin levels in the blood by decreasing their breakdown. Bradykinin is responsible for vasodilation.
Common Ace Inhibitors
In general, these medications help decrease cardiac output by limiting vasoconstriction and inhibiting aldosterone secretion promoting vasodilation. Common ACE inhibitors for patients with CHF are:
- Benazepril: given 10 mg once daily and gradually increased to 20-40 mg per day with a half-life of 10-11 hours and 12 hours respectively. If given with a diuretic the initial dose should be 5mg.
- Fosinopril: given 10 mg once daily and gradually increased to 20-40 mg per day with a half-life of 10-11 hours and 12 hours respectively. If given with a diuretic the initial dose should be 5mg.
- Captropil: given 25 mg 3 times daily and has a shorter half-life of 3.3 hours requiring the patient to take it more frequently.
- Rare: Hypotension and Renal Failure because ACE inhibitors are primarily excreted through the kidneys.
- Minor side effects, normally resolved with adjusting the dosage, include:
- Angioedema (an area of swelling of the lower layer of skin and tissue just under the skin or mucous membranes skin)
- GI discomfort
Implications for Physiotherapy
ACE inhibitors cause a reduction in BP this coupled with the naturally occurring post-exercise hypotension can result in excessive reductions in blood pressure. This can lead to dizziness and, in rare instances, syncope. Post-exercising clients on ACE inhibitors may need education in adhering to a gradual cool-down after each and every exercise session to prevent these symptoms and benefit the body by enhancing venous return and the prevention of blood pooling in the skeletal muscle. A gradual cool-down of five to 10 minutes of light aerobic activity allows the body to return to homeostasis and prevents excessive reductions in blood pressure.
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