Case 14 — Text

Text from “Small Animal Cardiovascular Medicine”

Cardiac Pacemaker Therapy

A pacemaker is a device that delivers battery-supplied electrical stimuli through electrodes in contact with the myocardium to produce an artificially triggered depolarization. Since the first implantable pacemakers were developed, the equipment and techniques available have improved dramatically, including new lead designs, microprocessor-based circuitry, long-life batteries, telemetric manipulation, and newer pacing routines allowing rate-responsive adaptations and dual-chamber pacing. Cardiac pacemakers are now much smaller and more durable, with batteries that can provide up to 12 years of continuous function. The most important technologic advance has been the refinement of percutaneous transvenous pacing leads that can be introduced through a peripheral vein, eliminating the need for thoracotomy.

Indications

The primary indications for artificial pacing are symptomatic bradyarrhythmias and conduction disturbances unresponsive to medical control. In veterinary patients, the most common arrhythmias treated include sinus bradycardia/sinus arrest (usually due to sick sinus syndrome or high vagal tone), high-grade second-degree and complete atrioventricular blocks, and persistent atrial standstill.

It is important for the clinician to understand that recognition of an abnormal ECG rhythm alone is not an indication for artificial pacing. In animals with documented ECG abnormalities and associated clinical signs (episodic weakness, syncope, etc.), artificial pacing is the preferred method when medical therapy is unrewarding. Due to the cost, potential complications, and life-long special care inherent to permanent artificial pacing, it is not always rational therapy in asymptomatic animals even when documented ECG abnormalities exist.

Contraindications

There are no absolute contraindications for pacemaker implantation; however, clinical and personal factors may preclude the decision to implant. Relative contraindications include debilitating generalized diseases and poor cardiac function secondary to a pre-existing cardiac disorder. The cost of new pacemaker hardware is prohibitive in veterinary medicine. The use of previously used generators and donation of outdated components by manufacturing companies provides free generators. Dogs with hyperadrenocorticism have more complications than dogs without, due to compromised immune function.

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