‘Heart attacks’ in humans and pets


When pets die suddenly owners may attribute it to a “heart attack,” but dogs and cats don’t really get heart attacks.

I got an unexpected crash course in a few aspects of human cardiology recently when I started experiencing tightness in my chest. At first I convinced myself it was asthma, but knowing my family history of heart disease, and knowing the signs of a heart attack can be very vague in women, and knowing too many folks who ignored those warning signs with dire consequences, I eventually went to the emergency room at the Martha’s Vineyard Hospital. Four hours later, my X-rays, ECG, and blood work showed no abnormalities and I felt better, but Dr. Zack was sternly adamant. I could go home now, but must go to Mass General ASAP for a nuclear stress test, an evaluation that involves injecting radioactive dye, then taking images of the heart before and after exercise. These pictures would allow cardiologists to see if any areas of my heart muscle weren’t getting adequate blood flow.

While making travel plans, I thought about cardiac disease in dogs and cats. It’s not uncommon when pets die suddenly for owners to attribute it to a “heart attack.” But dogs and cats don’t really get heart attacks, we tell them. Before we go further, a brief disclaimer.  Damn it, Jim, I’m a veterinarian, not a cardiologist. (Okay, please dismiss all Star Trek references as a side effect of my recent illness.)

Seriously. I’m not a cardiologist, but to the best of my understanding, in human medicine what people refer to as “heart attack,” is an acute myocardial infarction. Acute means it comes on suddenly. Myocardial means “of the heart muscle.” Infarction is tissue damage or death caused by lack of oxygen due to an obstruction of that tissue’s blood supply. So a human heart attack, a.k.a. acute myocardial infarction, is caused by sudden blockage of one or more of the coronary arteries leading to damage or death of part of the heart muscle.

Sudden death. It happens to pets now and then. One day your dog or cat, Valentine,  seems perfectly normal. The next, he keels over and dies. It can be devastating for owners, who urgently want explanations for such unexpected losses. Many people’s thoughts go immediately to poison, especially if Valentine goes outside unattended, but most toxins an animal is likely to encounter around here, such as rat poison and antifreeze, will typically cause clinical signs of illness before an animal dies. “He must have had a heart attack,” is another common conclusion. Wrong. Dogs and cats generally do not get coronary artery disease and thus do not get myocardial infarctions. Perhaps it’s their diet, lifestyle, or just genetics, but they appear to be resistant to this particular cardiac problem. That is not to say there aren’t other conditions that can lead to sudden death.

A sidebar on terminology. The term postmortem is short for postmortem examination, the dissection of a deceased body. It comes from the Latin post, meaning after, and mors, meaning death.  Another term for a postmortem on a human being is autopsy. This word comes from the Greek auto, meaning self, and opsis, meaning sight, or eyes. Thus autopsia meaning eyewitness, or seeing with one’s own eyes. The word autopsy was first used to describe the act of dissecting a cadaver to determine cause of death in around 1670 and is technically reserved for when this is done on human remains. For nonhuman animals, the proper term is necropsy, from the Greek nekros, meaning dead body. The point of all this being that if your pet, Valentine, bites the dust unexpectedly, your veterinarian is probably not going to be able to tell you why without performing a postmortem examination, correctly called a necropsy.

One cardiac condition often proposed to explain sudden death in dogs and cats is ruptured chordae tendineae, fibromuscular cords of tissue inside the heart that connect little mounds called the papillary muscles to the heart valves. They are sometimes poetically referred to as the “heart strings.”  If Valentine ruptures one of these heart strings, it can result in sudden death. Theoretically this occurs primarily when there is underlying disease of the heart valve, but we rarely get the opportunity to do a necropsy and/or postmortem laboratory diagnostics to get definitive answers. Perhaps Valentine died of a ruptured brain aneurysm. An aneurysm is a blood vessel with thinning walls that cause it to bulge abnormally. It can suddenly burst, leading to fatal hemorrhage. Even when we do perform necropsies, we rarely examine the brain, so this is another theory we seldom get to prove.

Other common fatal conditions are easier to demonstrate. Middle-aged large breed dogs are particularly prone to a form of cancer called hemgiosarcoma. There tumors affect the spleen or the heart and can often lead to sudden, fatal internal hemorrhage. Presumptive diagnosis can be made by simply tapping the abdomen, or pericardial sac, depending on the location of the tumor, with a needle and syringe and seeing if there is free blood in these places. Other causes of sudden death can include ruptured spleen from trauma such as being hit by a car, electrocution from biting electrical wires, acute conduction disturbances in the heart causing fatal arrhythmias, electrolytes imbalances from adrenal gland disease, and a variety of genetic problems Valentine might be born with but which don’t cause visible symptoms until he suddenly expires.

By the time I got to Boston, I had fairly constant angina. After an abnormal stress test, they quickly admitted me to the ER, then the cardiac ward. Three days later, I was given what they call “conscious sedation,” and cardiologists placed two stents via an artery in my arm into my coronary arteries, restoring adequate blood flow to the affected part of my heart. Amazing technology. The main thing I remember was the cardiologist yelling at me to stop asking so many questions. I guess I was curious. I know I was lucky. My heart gave me warning. No actual heart attack. No sudden death. Just gratitude.