Phoenix and Merlin - Feline Pacemaker

Phoenix (a black and white 16 year old male neutered domestic shorthair) and Merlin (a tabby and white 13 year old male neutered domestic long hair) both presented to Langford Vets Cardiology Service within 24 hours of each other in December 2023 for investigations of collapse episodes. Phoenix was diagnosed with intermittent third degree atrioventricular block by his local Cardiologist and referred on to us for treatment, and Merlin was diagnosed with intermittent third degree atrioventricular block following his investigations with us.

Both cats had surgery to place a pacemaker for this potentially life-threatening abnormal heart rhythm on the same day, and both cats have since recovered and are doing well. While it’s unusual for cats to need to have a pacemaker placed, to see two cases in less than 24 hours is extremely rare!

Phoenix (a black and white 16 year old male neutered domestic shorthair) and Merlin (a tabby and white 13 year old male neutered domestic long hair) both presented to Langford Vets Cardiology Service within 24 hours of each other in December 2023 for investigations of collapse episodes. Phoenix was diagnosed with intermittent third degree atrioventricular block by his local Cardiologist and referred on to us for treatment, and Merlin was diagnosed with intermittent third degree atrioventricular block following his investigations with us.

Both cats had surgery to place a pacemaker for this potentially life-threatening abnormal heart rhythm on the same day, and both cats have since recovered and are doing well. While it’s unusual for cats to need to have a pacemaker placed, to see two cases in less than 24 hours is extremely rare!

Intermittent third degree atrioventricular block is an abnormal heart rhythm. The electrical activity of the normal heart rhythm starts in the sinoatrial node and then spreads through the atria (the chambers that receive blood from the lungs and body), causing the atria to squeeze blood into the ventricles (the chambers that pump blood to the body and lungs). The electrical activity can only spread from the atria to the ventricles via the atrioventricular node. Once the electrical activity is through the atrioventricular node, it spreads through the ventricles causing the ventricles to squeeze blood out to the body and lungs. In both Phoenix and Merlin, the atrioventricular node had intermittently stopped working, resulting in no electrical activity in the ventricles and therefore no blood being pushed out to the body and lungs. This is why they were collapsing. If the ventricles don’t receive an electrical signal for more than a few seconds, the ventricles can often create their own electrical activity, but this is unstable and only results in a low heart rate.

Intermittent third degree atrioventricular block is an abnormal heart rhythm. The electrical activity of the normal heart rhythm starts in the sinoatrial node and then spreads through the atria (the chambers that receive blood from the lungs and body), causing the atria to squeeze blood into the ventricles (the chambers that pump blood to the body and lungs). The electrical activity can only spread from the atria to the ventricles via the atrioventricular node. Once the electrical activity is through the atrioventricular node, it spreads through the ventricles causing the ventricles to squeeze blood out to the body and lungs. In both Phoenix and Merlin, the atrioventricular node had intermittently stopped working, resulting in no electrical activity in the ventricles and therefore no blood being pushed out to the body and lungs. This is why they were collapsing. If the ventricles don’t receive an electrical signal for more than a few seconds, the ventricles can often create their own electrical activity, but this is unstable and only results in a low heart rate.

Patients with third degree atrioventricular block are at risk of developing an enlarged heart, congestive heart failure (fluid on or around the lungs causing breathing difficulties) and sudden death. Phoenix had an enlarged heart and had early evidence of congestive heart failure, whereas Merlin had some early enlargement of his heart. The best treatment for this abnormal heart rhythm is to place a pacemaker. Unlike in dogs, where the pacemaker lead is placed via the main blood vessel in the neck, cats have their pacemaker leads sutured on to the outside of the heart. The pacemaker in a cat sits in the abdomen, with the lead traveling through the diaphragm to the heart. Phoenix and Merlin had their surgeries performed on the same day, with both cats having x-rays to confirm position of the pacemaker afterwards (PHOTO) and then recovering in our Intensive Care Unit.

Patients with third degree atrioventricular block are at risk of developing an enlarged heart, congestive heart failure (fluid on or around the lungs causing breathing difficulties) and sudden death. Phoenix had an enlarged heart and had early evidence of congestive heart failure, whereas Merlin had some early enlargement of his heart. The best treatment for this abnormal heart rhythm is to place a pacemaker. Unlike in dogs, where the pacemaker lead is placed via the main blood vessel in the neck, cats have their pacemaker leads sutured on to the outside of the heart. The pacemaker in a cat sits in the abdomen, with the lead traveling through the diaphragm to the heart. Phoenix and Merlin had their surgeries performed on the same day, with both cats having x-rays to confirm position of the pacemaker afterwards (PHOTO) and then recovering in our Intensive Care Unit.