Welcome to September's Case of the Month! Here's a case involving the heart.

BE STILL MY BEATING HEART!

HISTORY

Erin was a 10-year-old Boxer who had been visiting us regularly for several years. Once, when she was in our office for a dental cleaning, we discovered an abnormal heart rhythm. Surprisingly, she had no sign of heart problems, and her heart rate and rhythm felt normal. However, an electrocardiogram (EKG, or ECG) revealed a serious problem.

EKG RESULTS

To help you compare, here's a normal EKG:

An EKG measures the normal electrical activity of the heart. Each time a part of the heart muscle contracts, or beats, an electrical signal accompanies it. These electrical signals show up as the humps, or "waves," on an EKG. With the first wave, the P wave, the atria contract. With the next wave (actually a group of three: Q, R, and S), the ventricles contract. And, with the final wave, the T wave, the heart muscle prepares to contract again.

On Erin's EKG, every other beat is abnormal. There are characteristics of EKG waves which tell us their origin: these abnormal beats arose in her ventricles. We took x-rays to evaluate her heart size, which was normal, and started her on an anti-arrhythmia medication. Another EKG a few weeks later showed this:

Better, but not perfect. Another EKG a few weeks afterwards still showed the arrhythmia, so we switched her to a different medication. The normal EKG shown above was hers, a month after starting the second medication.

DISCUSSION

Anything disrupting the heart's normal rate and rhythm is known as an arrhythmia. These can be caused by many things, including heart disease, trauma, drug reactions (including anesthetics), and electrolyte imbalances. In Erin's case, the cause was most likely early heart disease. She remained arrhythmia-free for about a year, but then started to have abnormal beats again (about 1 per every 3 normal beats). We're hoping we can adjust her medicine dose a little to straighten things out again.

FOLLOW-UP

Erin's heart rhythm had begun to revert to the abnormal state it had shown when she was first diagnosed with her problem. A couple of weeks after we'd increased her medication a little, her EKG looked liked this:

Much better! The only abnormal thing is that her heart rate is a little slow, and her owners reported she was acting a little sluggish. If you compare it with the normal EKG from before, you'll see fewer beats it the same amount of time:

This shouldn't be a problem, but we're looking at trying to reduce her medication again to find a balance between too slow of a heart rate and too many abnormal beats. It's been about a year since Erin was diagnosed, and she's still doing pretty well. Unfortunately, many pets with heart disease don't fare as well.

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