Early Detection of a Serious Heart Arrhythmia

By Susan Wootten, DVM

What started out as a routine recheck for a quiet heart murmur found at her annual visit in May turned into a life-threatening emergency visit for sweet Mia, an 11-year-old Greyhound. I found a grade 2/6 heart murmur during an annual comprehensive wellness visit in May. Because this was a new finding, I recommended that we have the heart murmur rechecked within 3-4 months. Heart murmurs are graded on a scale of 1-6 depending on how loud they are. If the murmur was found to be louder at this visit, or there were any other concerns with her heart rate or rhythm, additional diagnostics would be recommended at that time.

Mia's weight was down slightly at this visit, but overall her family reported that she had been doing well. When I listened to Mia’s heart with a stethoscope, I found that her heart rate was extremely elevated (over 200 when it should be less than 100) and that the rhythm was not normal. I ordered an ECG, also known as electrocardiogram, which is a diagnostic test which measures the electrical activity of the heart to show whether or not it is working normally. An ECG records the heart's rhythm and activity on a moving strip of paper or a line on a screen. Mia’s ECG test showed that she had a heart condition called ventricular tachycardia.

Ventricular tachycardia is a heart rhythm disorder (arrhythmia) caused by abnormal electrical signals in the lower chambers of the heart (ventricles). The heart rate is regulated by electrical signals sent across heart tissues. A healthy dog's heart normally beats about 80-120 times a minute when at rest and is defined by signals that originate in the upper chambers of the heart (atria). In ventricular tachycardia (V-tach), abnormal electrical signals in the ventricles cause the heart to beat faster than normal, usually 120 or more beats a minute, out of sync with the upper chambers. When that happens, the heart may not be able to pump enough blood to the body and lungs because the chambers are beating so fast or out of sync with each other that they don't have time to fill properly. In some cases, ventricular tachycardia can cause the heart to stop (sudden cardiac arrest), which is a life-threatening medical emergency. This condition usually occurs in dogs with other heart conditions, such as structural heart disease called cardiomyopathy.

Luckily, Mia's heart rhythm disturbance was caught during a routine medical progress exam. This allowed me to administer life-saving medications and reverse the arrhythmia. She was hospitalized briefly that day for further diagnostic testing including a cardiac ultrasound by Dr. Earley. Cardiac ultrasound, also known as echocardiography, is a 3-D image of the heart. The analysis of images is heavily technology driven as interpreting the diseases of the heart requires a rather detailed representation of everything that moves (cardiac muscles, valves, blood) within the heart. There is also a Doppler feature on the ultrasound that gives an analysis of valves and blood flow. The cardiac ultrasound showed that Mia had an early form of dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is a disease of the heart muscle that is characterized by an enlarged heart that does not function properly. With DCM, both the upper and lower chambers of the heart become enlarged, with one side being more severely affected than the other. When the ventricle, or lower chamber, becomes enlarged, its ability to pump blood out into the lungs and body deteriorates. When the heart’s ventricle does not pump enough blood, fluid can begin to accumulate in the lungs or in the abdomen. An enlarged heart soon becomes overloaded, and this can lead to congestive heart failure (CHF).

The major symptoms of DCM include lethargy, decreased appetite, rapid or labored breathing, shortness of breath, coughing, abdominal distension, and transient loss of consciousness. In some cases, dogs with preclinical (prior to the appearance of symptoms) DCM may be given a questionable diagnosis because they appear to be in fine health. On the other hand, a thorough physical exam can make apparent some of the subtle symptoms of DCM, such as pulse deficits, ventricular premature contractions, and slow capillary refill time. The dog’s breathing sounds may also have a muffled or crackling sound due to the presence of fluid in the lungs if they are developing early congestive heart failure. In Mia's case, she was preclinical at home, but during her examination, was found to have the life-threatening arrhythmia. Had it gone undiagnosed for much longer, she could have succumbed to sudden death at home.

Mia was started on several heart medications, two to help with the underlying heart condition, and another to help with the arrhythmia. At her recent medical progress exam, Mia was doing great. Her family reported a huge increase in her energy level and the arrhythmia was found to be well controlled with her current medications. Mia's story stresses the importance of routine annual wellness examinations for your pet and recommendations by your veterinarian for any future follow up that may prevent a life-threatening disease.