Test Your Knowledge Cardiac Conundrum

Question 8

A 6-year-old neutered male Labrador presents to you with a 2-week history of exercise intolerance and a collapsing episode 2 hours before presentation. The collapse happened when the dog tried to chase a cat. The dog seemed unconscious to the owner, there was no tonic or tonic-clonic activity and the collapse episode lasted less than 30 seconds with a fast and complete recovery afterward.

On physical examination the heart rate was 40 bpm with a regular and strong femoral pulse, no cardiac murmur was detected and the clinical examination was otherwise unremarkable. You performed an ECG to characterize the bradycardia.

What’s your ECG diagnosis? And, what is the most appropriate treatment for this patient?

Answer

The ECG shows a complete atrioventricular dissociation (P waves are not associated with the QRS complexes) with a slow ventricular escape rhythm. This is a third degree atrioventricular block (complete AV block). The recommended treatment for complete AV block is a pacemaker implantation.  

Third degree AV block is the most common indication for pacemaker implantation. In veterinary cardiology the most frequently implanted pacemaker system is a rate-responsive, single chamber and single lead (VVIR) pacemaker.