Mark D. Kittleson, D.V.M., Ph.D. explains how SVT may present itself.
Supraventricular tachycardia (SVT) is defined as repetitive supraventricular premature depolarizations (SPDs). As with SPDs, SVT can originate from atrial myocardium or AV junctional tissue. They most commonly occur in humans because of reentry, although automatic SVT can occur...Few electrophysiologic studies have been performed in dog, but response to therapy (most SVTs respond to calcium channel blocker administration) suggests that reentry is also the most common mechanism underlying SVT in the dog
I spoke before about the ties between the symptoms of my own SVT and that in canine STV. If you missed that post, the layperson's description for the clinical one you just read is that SVT presents itself as a sudden, rapid heart rate for no apparent reason. It can be mild or severe. In my case, it was severe and required medical treatment.
After my hospital visit discussed in the previous post, I was referred to a cardiologist who discussed the possibility of SVT and recommended I wear a Holter Monitor for several weeks. As Wikipedia describes it, a Holter Monitor "records electrical signals from the heart via a series of electrodes attached to the chest...these electrodes are connected to a small piece of equipment that is attached to the patient's belt or hung around the neck, and is responsible for keeping a log of the heart's electrical activity throughout the recording period. A company would monitor my heart rate, and I would be required to call them to report any symptoms.
I wore the monitor and alarmed fitness instructors at the gym and many of my friends. I called the people monitoring my heart whenever I felt symptoms, and it quickly became apparent that I needed to put them in my "favorites" list on my phone. When I actually had to physically take action by calling the monitoring facility, it made me realize exactly how often my symptoms were presenting, which was several times a day. Considering that most SVT patients present symptoms only once every few weeks, my condition was fairly alarming.
When I returned to the doctor after the monitoring period, she said "I don't know how you're living like this. I've rarely seen a case this severe." She officially diagnosed me with supraventriciular tachardia, or SVT.
SVT is typically a genetic condition, and it is congenital, meaning that you have to be born with it. Symptoms typically don't appear until adolescence, but that isn't always the case. Though not normally life-threatening, my SVT was so frequent that my cardiologist advised me to have a cardiac ablation as soon as possible. She suspected that I had multiple extra electrical connections that contributed to the severity of my condition, and she advised me not to have any more children until I had the procedure done since hormones are a contributing factor. Lucky for me, I was done having kiddos. Even so, the fact that my heart was so over-taxed on such a regular basis was not good. My heart needed a break, and so did I.
Long-term SVT can lead to progressive myocardial (heart muscle failure) or congestive heart failure in humans and dogs.
Regarding Canine SVT, PetMD.com says
SVT may go unnoticed when it is periodic, but where there are repetitive supra ventricular premature electrical heart depolarizations (changes in the heart's electrical potential) that originate from a site other than the sinus node (the pacemaker of the heart), such as the atrial muscle or atrioventricular nodal tissue, the condition can become a serious health problem.
When Canine SVT is slow or infrequent, there may be no clinical signs, but dogs with fast SVT (a heart rate greater than 300 beats per minute) may exhibit weakness or fainting. Dogs with congestive heart failure may cough or have breathing abnormalities.
SVT in dogs is also thought to develop due to a genetic predisposition or for unknown reasons, but PetMD states that other factors may contribute to the condition, including
• heart disease
• digoxin toxicity
• systemic disorders
• electrolyte imbalances
• abnormal automaticity in ectopic focus (when the heart beats prematurely or outside the normal parameters)
In order to reach a diagnosis, a veterinarian will do a thorough physical exam of your dog. That exam, in combination with the symptoms you report, is critical, as dogs typically won't tolerate wearing a monitor for weeks on end (heck, I could barely tolerate it). Long-term monitors are used in some canine cases. Laboratory tests will also help the veterinarian diagnose Canine SVT. These tests include a biochemical profile, bloodworm, a urinalysis, and an electrolyte panel, which rules out other diseases. The veterinarian may also use an electrocardiogram (EKG) recording to take a more in-depth look at the electrical currents in the heart muscles. The EKG may show abnormalities in the heart's beating ability.
When I received my diagnosis, I had a mixed sense of terror and relief. My condition was serious, which was frightening, but death was not imminent, and I finally had a name and medical description for what I was going through, which helped me feel more settled about my symptoms. I imagine pet parents of dogs with Canine SVT would feel the same way.
Mystery solved. Now, what?
In part three of this series, we'll discuss the treatment.