Visiting Veterinarian : A slow pulse can stump the best vets on Martha's Vineyard
When Zev, a middle-aged cockapoo, developed a mild cough recently, his owner wasn't too concerned at first. Probably just allergies, she thought. Goldenrod was in bloom, the pollen count high. But after a few days, he started coughing nonstop. My office was closed for the weekend so his mom contacted the veterinarian covering emergency calls, who saw them right away.
On exam, Zev's temperature was slightly elevated. The emergency doctor couldn't have known that Zev normally runs a hair warmer than your average dog, but what clearly wasn't normal was his heart rate. It was slow. Really slow. Reeaaally ssllooww.
Now I wasn't in that exam room at that clinic at that time, but I have been in similar situations and can picture myself in that scenario. Here's this dog who's coughing, maybe a little out of breath. He's high-strung, even a bit uncooperative, and appears to have a low-grade fever. I put my stethoscope up to his chest, assuming he's suffering from something routine. Something easy. Like kennel cough. Lub dub. Waiting. Waiting. Waiting. Where's the next heart beat? I move my scope around to find a better spot. Lub dub. Waiting. Waiting. Uh-oh. I start counting beats, and think to myself "Drat, drat, drat. This ain't a simple case of kennel cough."
Bradycardia is the technical word for an abnormally slow heart beat. It's a descriptive term, not a diagnosis, and the seriousness depends on the underlying cause. The normal heartbeat is controlled by electrical impulses that travel through the muscle at regular intervals. This creates a steady rhythm that may vary slightly with respiration, but is consistent. Normal heart rates for dogs range from 60 to 160 beats per minute. Smaller dogs tend to have higher rates. Large athletic dogs, slower. Zev's heart rate was — lub dub — wait for it — 40 beats per minute.
There are many things that can cause such an unusually slow heart rate. The veterinarian on call got a full history, performed a complete physical, took blood tests, radiographs, and an electrocardiogram. This thorough work-up ruled out many etiologies such as the adrenal gland disorder known as Addison's disease, exposure to various drugs, and Lyme disease. The ECG revealed atrioventricular (AV) block, a situation in which the electrical impulse gets stopped en route from one part of the heart to another.
Again, this is a description of what is happening, not an explanation why. AV block causes a slowed heart rate. The slow heart rate causes reduced cardiac output. The heart isn't pumping sufficient blood around the body. Blood carries oxygen, without which nothing works right. Affected animals may get winded easily, be lethargic, have fainting spells. They may even collapse and die suddenly.
Zev's owner was advised to consult a veterinary cardiologist immediately and to consider having a pacemaker implanted. Having gone in expecting a diagnosis of something relatively inconsequential like pollen allergies, she was understandably overwhelmed and needed time to think. Zev was already more than 11 years old.
"I'd hate to put him through any major invasive procedures," she confided two days later, when she came to discuss the options with me. She shared that her father had needed a pacemaker, and the experience had been difficult. "Besides, Zev's cough is almost completely gone," she said, looking at me hopefully. "See how great he's feeling?"
Zev did, indeed, look fine. Completely fine. Tail wagging. Full of energy. I grabbed my stethoscope. Lub dub. Waiting, waiting, waiting. Lub dub. His heart rate was still abnormally low. Forty-five beats per minute.
We opted to consult a cardiologist electronically by sending an ECG over the telephone, followed by a procedure called an Atropine Response Test (ART.)
I'll spare you the pathophysiology lesson. Suffice it to say Zev's heart rate did not improve with the ART, thus giving us one more piece of the puzzle and a differential diagnosis of idiopathic cardiac fibrosis or sick sinus syndrome, two similar conditions that occur occasionally in cocker spaniels. Neither has any definitive treatment other than pacemaker implantation. No one knows exactly why cockers get these problems, but as breed-specific occurrences, it is suspected they are genetic and inheritable. Rarely, cancer or infection may be implicated, but Zev showed no indications of such underlying illnesses.
His mother agonized over the decision. "What will happen without a pacemaker?" she asked somberly. After discussing Zev's situation with several cardiologists on-line, I answered her question. Sort of.
"One cardiologist says that without a pacemaker Zev has a significant risk of sudden death within the next year or two," I stammered. "The other cardiologist thinks the prognosis may not be so grave. In his opinion, as long as Zev isn't showing any symptoms, we can sit tight. He may even live for many years."
As far as giving medication that might increase his heart rate, the cardiologists concurred that the only reason to use such drugs would be if Zev developed obvious symptoms affecting his daily quality of life, such as fainting spells. "One more thing," the owner added, pointing out to me a lump the on call veterinarian had found in Zev's neck.
"We can't tell if it's benign or malignant without a biopsy," I said. "But in either case, anesthesia and surgery is too risky without that pacemaker."
Three days after the initial diagnosis, the cough which had prompted Zev's mom to get him evaluated, leading to discovery of the bradycardia, had completely resolved. Maybe it had been just pollen allergies. Or kennel cough. In any case, it was apparently unrelated to his heart condition. Zev looked fine — energetic and playful. Unless you happened to have a stethoscope, you'd never know anything was wrong with him.
But his mom knows that her little cockapoo could pass away suddenly at any moment. We're going to monitor the lump, take life one day at a time, and hope over the coming months and years that the more optimistic cardiologist will be proven right.