Heart Failure in Horses

A clinical condition, heart failure is a secondary occurrence resulting from significant, overpowering heart disease. Heart failure is a condition where there is clogging or atypical collection of fluid, a decrease in blood flow to the body, and your horse has very low blood pressure. In most cases, heart failure is due to chronic illness that has led to significant issues causing the heart to be unable to pump enough blood. Heart failure is considered rare in horses.

A result of significant heart disease, heart failure will occur should the heart not be able to keep up standard venous and capillary pressures, cardiac output, and the system’s blood pressure.

Should your horse be experiencing heart failure, the following symptoms may be seen:

• Heart murmur and rapid heart rate
• Enlarged jugular veins
• Throbbing of the jugular veins
• Coughing
• Rapid breathing
• Lack of appetite
• Lack of energy
• Weight loss
• Swelling along the surface of the abdomen of your horse
• Swelling of lower limbs
• Weakness
• Restless during sleep
• Inability to exercise
• Collapse

Types 

Heart failure is divided into four classifications:

Systolic myocardial failure

The heart muscle’s ability to contract is reduced. If the reduction is severe, regular blood flow is unable to be kept up. This can happen as a result of trauma, infection, drugs, poisons, electric shock, heat stroke or tumors.

Obstruction to cardiac inflow

This leads to blood flow decreasing possibly caused by the heart being compressed, perhaps due to:

• Fluid in the sac that surrounds the heart
• A problem in the widening of the chambers of the heart between two contractions that causes a still ventricle and decreased ventricular filling
• Anomalies to the heart’s structure

Pressure overload

This can happen due to long term increases in stress impacting the heart wall when contracting, causing blood flow from the heart to be blocked or an increase in blood pressure.

Volume overload

This can occur due to any disease that multiplies the amount of blood in the ventricles(s) which leads to a greater amount of blood flow and can cause congestive heart failure. This includes valve disease and left-to-right shunts.

Heart failure is, in most cases, a result of a chronic disease that leads to a significant reduction in the heart’s contractions, significant regurgitation or shunting or significant diastolic dysfunction.

While not a distinct disease, heart failure is considered to be a syndrome where significant dysfunction resulting from one of the many types of heart disease leads to the cardiovascular system being unable to circulate blood to the extent necessary. Certain workings impacted by heart disease can lead to cardiovascular system failure; however, heart failure is not a specific diagnosis. Often, the heart of your horse would be found to be enlarged upon undergoing an echocardiogram; the clinical signs that are seen the most in heart failure are a direct result of swelling or effusion.

Your horse may have heart disease without it leading to heart failure, though heart failure can only happen in your horse if he has heart disease.

When considering treatment for heart failure, your veterinarian will look to improve the operation of the heart muscle, regulate arrhythmias and blood pressure, enhance blood flow, and decrease the volume of blood that fills the heart prior to contraction. Should these not be regulated, further damage to the heart and blood vessels may occur. Treatment will also seek to decrease the volume of fluid that is present in the lungs, abdomen, and chest cavity of your horse.

A variety of medications are available when looking to treat heart failure. Your veterinarian will consider the cause and extent of your horse’s heart failure when looking at which medication, dose, and how often it will be administered. 

• Diuretics are typically prescribed in order to decrease excess fluid
• Medications that help the heart muscle contract, like digitalis and digoxin (from the category of drugs called positive inotropes) may be recommended
• Angiotensin-converting enzyme (ACE) inhibitors and vasodilators work to broaden blood vessels, helping to decrease blood pressure
• Beta-adrenergic blocking drugs (beta-blockers) as well as calcium channel blockers may be of use
• In some cases, surgical measures may be recommended to remove fluid buildup

Should your horse be experiencing heart failure, you will want to work closely with your veterinarian; it is important to administer all medications as directed and attend follow up appointments as discussed. Medications may not be effective if not given at appropriate timeframes and not following your veterinarian’s instructions can lead to further problems for your horse.