A heart attack occurs when the blood flow to a section of the heart muscle becomes blocked, permanently damaging the heart. Heart attacks are typically caused by coronary artery disease, in which plaque builds up on the inside walls of the coronary arteries. Coronary arteries supply blood and nutrients to the heart. Because the vasculature around a cat's heart is different from a person's, cats rarely, if ever, suffer from a true heart attack. However, they can suffer from and die of heart disease.
Many times, if pet owners are told their cat had a heart attack or died of a heart attack, it's a layman's term for the cat having cardiomyopathy, which literally translates to "heart muscle disease." This autoimmune disease inflames the heart muscle, which prevents it from generating the normal force of contraction and affects how well it pumps.
Types of Cardiomyopathy
There are three main types of cardiomyopathy: dilated, hypertrophic and restrictive. The one most commonly found in cats is hypertrophic cardiomyopathy.
Hypertrophic cardiomyopathy causes an abnormal thickening of the heart muscle. This reduces the amount of blood the heart can pump with each beat, making it hard for the blood to pump out of the heart. It can also affect electrical function, causing arrhythmia (irregular heartbeat).
Dilated cardiomyopathy involves enlargement of the heart chambers, affecting the heart's ability to pump blood.
In restrictive cardiomyopathy, the walls of the heart become rigid due to scarring, restricting the muscle from stretching and filling with blood.
Clinical signs sometimes include a heart murmur (extra or unusual sound during a heartbeat) or pulse over 200. The type of cardiomyopathy your cat has will determine what other symptoms may be present.
Symptoms of dilated cardiomyopathy may include abdominal swelling due to fluid retention, coughing, shortness of breath or difficulty breathing, weight loss and fatigue.
Most cats with hypertrophic cardiomyopathy will be asymptomatic or mildly symptomatic. If the cat is symptomatic, it may experience dyspnea (difficulty breathing, panting, open-mouth breathing), lack of appetite, vomiting, exercise intolerance, fainting or extremely painful rear limb paralysis due to blood clots. In some cats, the only symptom may be a sudden cardiac death.
Cats with restrictive cardiomyopathy may experience lethargy or dyspnea.
Heart disease can occur in cats as young as 3 months or as old as 19 years. Middle-aged male cats of 5 to 7 years have the highest risk. It is largely genetic. But, there are also acquired forms of heart disease. For example, hypertrophic cardiomyopathy is often linked with hypothyroidism (slow thyroid function). Taurine deficiency used to be the main cause of dilated cardiomyopathy. Now that commercial cat foods have added taurine, dilated cardiomyopathy is rare and will generally only occur in older male cats. Restrictive cardiomyopathy mostly occurs in older male cats (around 10 years of age).
The prognosis for cats that suffer from heart disease varies. It depends on what type of heart disease and how serious it is when diagnosed. However, it is hard to diagnose heart disease in cats because they tend to change their habits to mask signs. Sometimes, there are no signs. Some cats may live up to six years with an undiagnosed heart condition. Many times, owners never know their cats have a heart condition until a sudden cardiac death occurs and it is discovered postmortem.
Dilated cardiomyopathy is serious and the mortality rate, even of treated cases, is very high. The median survival rate is about two weeks for cases that aren't related to a taurine deficiency. However, for DCM caused by taurine deficiency, if the cat can be kept alive long enough for taurine supplements to become effective (two to three weeks), the prognosis is better.
If your cat develops aortic thromboembolism, a common complication associated with all forms of cat heart disease, the median survival time is about 61 days. A thrombosis is a blood clot. An embolism is when the clot lodges within a vessel. For cats with heart failure, the median survival time is 92 days. Cats with a resting heart rate of less than 200 live longer than cats with a resting heart rate over 200.