Case Studies In Small Animal

Cardiovascular Medicine

ECG 22

Signalment: Seven-year-old spayed female Pit Bull Terrier (Brandy)

Presenting complaint: Episodic collapse during or following exercise

ECGs taken upon presentation (2)

Quiz

Correct Quiz

ECG taken under anesthesia while being temporarily paced from the right ventricle and with a recording electrode in the right ventricle

ECG taken under anesthesia while being temporarily paced from the right ventricle and with a recording electrode in the right atrium

ECG taken under anesthesia while being temporarily paced from the right ventricle and with a recording electrode in the right atrium - catheter with electrode is touching right atrial myocardium between QRS complexes # 2 and #4

The dog was anesthetized and a temporary pacing lead placed in its right ventricle that was the connected to a temporary pacing generator. An electrode catheter was then introduced into the right heart. Recordings from both the right ventricle and right atrium revealed atrial flutter but with very small complexes. When an attempt was made to pace the heart from the right atrium, there was no response. Occasionally when the electrode catheter touched certain parts of the right atrial myocardium, larger electrical deflections were recorded. A diagnosis of persistent atrial standstill was made. In this disease the myocardium is mostly destroyed by some disease process that leaves only fibrous tissue behind. It was thought in this dog that there was still some functional myocardium left that generated feeble atrial flutter that was unable to generate enough electrical force to traverse the AV node to produce ventricular depolarizations so the AV node and Purkinje fibers had to take over the pacing function for the heart. Some islands of myocardial tissue could still be directly stimulated by physically touching the myocardium with the catheter.

See Case 11 - Electrograms for a similar case with the intracardiac electrograms.