RA=Right atrial lead, LV = left ventricular lead placed in a coronary vein, RV = right ventricular lead. This the most advanced pacemaker that has three leads, shown here in a dog; however, most pacemakers placed will only have the RV lead and work well improving the quality and longevity of a patient's life.
Just like people, some pets need a pacemaker to keep their hearts ticking. This article provides general information about why a pet might require a pacemaker, and how pacemakers are implanted.
Why Would my Pet Need a Pacemaker?
Normally, the heart sends a repetitive electrical signal through its muscle cells, which stimulates the muscle to contract and pump blood through the body, much like a car's spark-plugs provide the spark that ultimately causes the pistons to move. This signal is carefully coordinated and regulated.
Occasionally, however, the signal is disrupted. Heart block and sick sinus syndrome are the two most common causes of such a disruption, resulting in erratic discharge of the signal or a complete failure of it. This disruption causes a slow heart rate because without the regular spark-plug, “emergency life-support back-up systems” take over to keep the heart beating enough to stay alive.
When such a disruption occurs, the pet usually develops exercise intolerance, collapses or faints. Because many of these pets are older, owners sometimes attribute more subtle signs of slowing down to aging when in fact it is due to a slow heart rate.
The solution for these pets is to “rewire” their heart with a pacemaker that provides the regular electrical signals. Almost universally, pets needing a pacemaker improve clinically (often quite dramatically) once the pacemaker is implanted and adjusted. Without a pacemaker, clinical signs often worsen, and the pets usually succumb to their disease within 1 to 2 years. Pacemakers can often extend this survival by several years, depending on the overall health of the pet.
Non-related disease usually does not prevent use of a pacemaker.
What is a Pacemaker and how is it Placed?
A pacemaker is made up of a pulse generator (a small computer and battery) and specialized wires called pacing leads. The pulse generator is about the size of a silver dollar, only thicker, and contains an energy supply and a computer that monitors and controls the rhythm of the heart. The leads transmit electrical impulses in both directions between the pulse generator and the heart, so that the pulse generator “knows” when to send an impulse and when to wait.
Pacemakers used in pets are identical to those used in people; the only difference is that they are usually obtained from the manufacturer after the shelf-life of the power source has decreased below acceptable limits for use in people. Because of the generally shorter life span of animals, these pacemakers can be successfully implanted in pets at a substantially lower cost than if a new pacemaker was being implanted; new pacemakers in people cost upward of $10,000, while those in pets are often around 10% of this cost.
The pacemaker lead is typically placed through the jugular vein in the right side of the neck, down into the inside of the heart and attached the heart wall. Occasionally, the pacemaker lead may be placed through the diaphragm and attached to the outside of the heart; this method is mainly used in cats. Some dogs may have one pacing lead, while others will have multiple pacing leads, depending on the heart problem and the size of the patient. The type of pacemaker used, its placement, and number of pacing leads is decided by the cardiologist implanting the system. If the lead is placed through the jugular vein, the pulse generator is placed in a pocket under the skin – usually on the side of the neck. If the lead is placed through the diaphragm, the pulse generator is attached to the inside of the abdominal wall.
Prior to anesthesia but while under sedation, a temporary pacemaker is placed so that the pet’s heart rate can be controlled during anesthesia. Since this is a modestly risky procedure, complications can occur. These include problems under anesthesia, such as abnormal heart rhythms, puncture of the heart or vessels, infection, or rarely death during the procedure. Once the pacemaker is implanted, it may stop functioning if the pacing lead becomes dislodged, or the strength of the impulse provided by the generator is too low. Most of these problems can be corrected.
What Special Care is Needed once my Pet comes Home?
Initially, rest and recuperation are advised while the pacemaker and the lead “heal” into place. After a couple of weeks, the stitches are removed, and normal activity can be resumed. Usually at this time, the pacemaker is adjusted to provide an appropriate signal (not too big as that would waste battery power and not too small as that could fail to stimulate the heart). This adjustment is done by the cardiologist using a device that checks the pulse generator through the skin. It is completely painless.
Occasionally, a swelling develops over the site where the pulse generator has been implanted. If this occurs, consult the cardiologist who implanted the pacemaker. Under no circumstances should your local veterinarian address this issue without consulting the cardiologist. It is usually a simple problem to deal with, if handled correctly.
While petting, you will be able to feel the pacemaker under the skin; it feels like a flat hard metal disc. It's usually located on the side of the neck or over the shoulder blade.
What Should Pets with Pacemakers Avoid?
Microwaves are not a danger to your dog (microwave energy can sometimes cause undesirable currents to flow in the pacemaker's electric leads, but generally dogs are not tall enough to be affected). However, if your dog has a pacemaker and requires advanced imaging, such as a magnetic resonance imaging (MRI), it is important to notify the cardiology service before the scan because the MRI will negatively affect the pacemaker. There may be precautions that can be taken to either shield the pacemaker, or know that it will temporarily "malfunction" if going into an MRI. It is probably best for the cardiology department to determine the risk on a case-by-case basis.
Dogs with pacemakers should avoid metal detectors, and strong electrical or magnetic fields of any sources (i.e. power plants, junk yards). In addition, cell phones should be kept at least a minimum of 6 inches away from the pacemaker generator at all times to avoid interference, even when the phone is turned off.
With rare exceptions, bumping the pacemaker won't affect it, so don't be afraid to let your dog play as desired.
How often does my Pet Need to be Examined?
Rechecks to evaluate pacemaker function and battery life are usually performed several times in the weeks following pacemaker implantation and then yearly. Additional rechecks are recommended at your doctor’s discretion, or if your dog becomes weak or collapses.
(Co-authored by Herbert Maisenbacher, VMD, DACVIM-Cardiology and Mandi Schmidt, DVM)
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