Why Are Diuretics Used in Heart Failure?

Heart failure can cause edema when extra fluid seeps into the lung cavity or other cavities. Diuretics treat this symptom, but do not cure heart failure.

Congestive heart failure is a condition in which the heart is unable to efficiently pump blood to meet the body’s oxygen and nutrient needs. This impairs normal blood circulation and leads to excess fluid in the blood. The excess fluid leaks out of the blood vessels and accumulates in the lungs and other tissues.

Congestive heart failure is a progressive disease and has to be managed with medication and lifestyle habits. The primary symptoms of congestive heart failure include:

• Shortness of breath (dyspnea) from fluid collection around the lungs,
• Swelling of lower limbs (peripheral edema)
• Fatigue and reduced capacity for exercise

Diuretics, also known as water pills, are medications that promote urination and reduce fluid retention in the body. Diuretics inhibit the kidney from reabsorbing sodium, which normally happens during blood filtration. The release of sodium also leads to the elimination of excess fluid by way of increased urine output.

Diuretics are an integral part of heart failure treatment, along with other medications to treat the underlying cause of heart failure. Diuretics help the kidneys flush out the excess fluid and maintain normal blood volume.

The elimination of excess fluid reduces pressure in the veins and the overload of venous blood into the heart. As a result, the heart requires less effort to pump out blood, and the blood pressure in the arteries drops. The fluid accumulated in the lungs and other tissues drains back into the circulation, providing symptom relief. 

Studies show that diuretics improve blood flow and reduce the symptoms of heart failure, but do not clearly demonstrate an improvement in mortality in heart failure or arrest in disease progression with diuretic use. The effectiveness of diuretics may be limited by some of their adverse effects.

The kidney is made up of microscopic functional units known as nephrons. The nephrons produce certain proteins which help filter the wastes from the blood, and reabsorb minerals such as sodium, potassium and chloride for circulation in the blood. Diuretics inhibit the nephron’s proteins, inducing the kidneys to flush minerals along with excess water.

Certain classes of diuretics flush out potassium in the urine, which can lead to low potassium levels in the blood. Potassium-sparing diuretics, on the contrary, may increase potassium levels. An imbalance in the blood potassium level can cause irregular heartbeat, and must be monitored.

Diuretics may be taken as pills for early stages of heart failure, but may be administered intravenously for hospitalized patients. People who take diuretics on a long-term basis must regularly check their kidney function and electrolyte levels because of the extra urine output and loss of minerals.

People may develop resistance to diuretics gradually, in which case a combination of diuretics may be effective.

Loop diuretics

Loop diuretics inhibit a protein found in a part of the nephron known as the loop of Henle. Currently available loop diuretics include:

• Furosemide (Lasix)
• Bumetanide (Bumex)
• Torsemide (Demadex)
• Ethacrynic acid (Edecrin)

Ethacrynic acid is rarely used except by those with sulfa allergies, as the other three are sulfonamide diuretics.

Thiazide and thiazide-like diuretics

Thiazide diuretics are commonly used to treat high blood pressure (hypertension), but also to manage heart failure. Thiazide diuretics inhibit a different protein than the loop diuretics do, which also helps in mineral reabsorption. Thiazide diuretics include:

• Chlorothiazide (Diuril)
• Hydrochlorothiazide (Hydrodiuril)
• Metolazone (Zytonix) – thiazide-like
• Potassium-sparing diuretics (aldosterone antagonists)

Aldosterone is a hormone produced by the adrenal gland, which activates sodium absorption and potassium removal. Aldosterone antagonists block the release of aldosterone, preventing sodium absorption as well as potassium depletion. Following are the aldosterone antagonists currently available in the US:

• Spironolactone (Aldactone)
• Eplerenone (Inspra)
• Amiloride (Midamor)
• Triamterene (Dyrenium)
• Carbonic anhydrase inhibitor

A carbonic anhydrase is an enzyme that balances the blood pH levels. Carbonic anhydrase inhibitors block the enzyme, promoting the excretion of sodium, potassium, bicarbonate and water. The carbonic anhydrase inhibitor used for heart failure is:

• Acetazolamide (Diamox)

Non-diuretic alternatives

• Vasopressin antagonists: Vasopressin antagonists are a new class of drugs being studied for use in heart failure. This class of drugs works by blocking vasopressin, which is an antidiuretic hormone produced by the pituitary gland.
• Ultrafiltration: Ultrafiltration is the removal of excess fluid in the blood with the use of a machine. A catheter placed in the vein carries the blood to a filtration machine and brings it back into circulation after the removal of excess fluid.

Diuretic use for heart failure carries some risks because the loss of minerals can cause electrolyte imbalance and lead to conditions such as:

• Hypokalemia: Low potassium 
• Hypomagnesemia: Low magnesium
• Hyponatremia: Low sodium
• Hypercalcemia: High calcium
• Hyperuricemia: High level of uric acid
• Hypochloremic metabolic alkalosis: Increase in pH level because of chloride loss
• Hyperkalemia: High potassium from potassium sparing diuretics

Side effects include:

• Frequent urination
• Extreme tiredness and weakness which may resolve as the body gets used to the medication
• Dehydration
• Dizziness
• Headaches
• Muscle cramps
• Blurred vision
• Nausea and vomiting
• Irregular heartbeat