Resolution of sustained narrow complex ventricular tachycardia and tachycardia-induced cardiomyopathy in a Quarter Horse following quinidine therapy.

This research focuses on a case where a fifteen-year-old Quarter Horse suffering from sustained narrow-QRS tachycardia and left ventricular systolic dysfunction was successfully treated using quinidine therapy, after initial attempts with intravenous diltiazem and lidocaine failed. The study demonstrates the potential of the rhythm-control drug quinidine in resolving such heart conditions in horses.

Details of the Case

• A fifteen-year-old Quarter Horse was diagnosed with a sustained form of narrow QRS tachycardia, a specific type of abnormal heart rhythm, and left ventricular systolic dysfunction, a condition where the heart’s main pumping chamber is unable to contract forcefully.
• This condition had been present for three months, and no structural cardiac anomalies or underlying causes for the tachyarrhythmia were evident by echocardiography, a diagnostic tool that uses sound waves to produce images of the heart.

Initial Treatment

• The initial course of treatment involved the administration of intravenous diltiazem and lidocaine, both medications commonly used to control heart rate and stabilize heart rhythm.
• However, the medications did not lead to successful conversion, implying that they were not effective in restoring the horse’s heartbeat to a normal rate and rhythm.

Quinidine Therapy

• Subsequently, the horse was treated with quinidine, an oral medication more commonly used in human cases for the treatment of certain types of heart rhythm disorders.
• This therapy successfully converted the horse’s tachyarrhythmia, indicating that it was effective in restoring a regular heart rhythm.

Outcome and Interpretation

• Following the successful treatment, the ventricular systolic dysfunction and enlargement of the heart chambers were resolved.
• This shows the potential of quinidine as a successful treatment for similar cardiac issues in horses where other medications are ineffective.
• The researchers assert that, as with other species, echocardiographic features of dilated cardiomyopathy (heart muscle disease) in horses may be induced by tachycardia and could potentially be resolved following successful control of heart rate and rhythm.