Interventional cardiology is a branch of cardiology that deals specifically with the catheter-based treatment of structural heart diseases. Interventional cardiology techniques have revolutionised our ability to treat specific cardiac diseases avoiding open surgery which might be associated with more complications. These include treating patients with patent ductus arteriosus, pulmonic stenosis and arrhythmias.
The majority of these procedures are performed under fluoroscopy guidance (dynamic X-ray machine) and will require an angiography study (technique used to visualize the inside of blood vessels with particular interest in the arteries, veins and the heart chambers). This is traditionally done by injecting a radio-opaque contrast agent into the blood vessel or inside the heart.
Pacemaker implantation for bradyarrhythmias (abnormally low heart rate) such as high-grade atrioventricular block, atrial standstill and sick sinus syndrome has become a routine interventional procedure and leads to the patient then going on to have a normal active life.
A pacemaker is an electronic device that maintains the heart rate by stimulating the heart to contract when the heart’s own electrical activity fails to do so.
The pacemaker works on demand. This means it has the ability to monitor the heart rhythm and if the heart intermittently stops the pacemaker will kick in at these times to keep it going. Pacemakers can also detect movement and increase the heart rate when needed like during exercise (rate-responsive pacemaker). Typically, a pacemaker is set to have a heart rate range of 60/min to 160/min.
Before recommending pacemaker implantation, our Cardiologists will check the medical history provided by your Vet as well as the results of any diagnostic tests such as bloodwork, ECG and chest x-rays. They will also perform a thorough clinical examination and cardiac ultrasound scan to check for any underlying problems that might be the cause of the abnormally low heart rate or that might compromise long-term outcome.
In dogs the procedure is performed via 2 small incisions on the neck with the pacemaker lead being inserted into the jugular vein and advanced to the bottom of the right ventricle where it delivers the electrical ‘spark’ that creates the heartbeat. The actual pacemaker is implanted under the skin on the neck.
Pacemakers can be implanted in cats as well, however the battery is usually placed at the level of the abdomen in a pocket in between the wall muscles. The lead is then attached to the outside of the heart passing through the diaphragm.
The pacemaker continuously monitors the heartbeat and delivers electrical energy to pace the heart if it’s beating too slowly. The pacemaker can be programmed to suit the needs of the patient
Your dog will return home few days following surgery with a large bandage around the neck. The bandage protects the operation sites from being scratched, helps to reduce any swelling, protects against infection and restricts head movement (minimising the risk of lead displacement, which is the major complication in the first weeks).
Infection is a potentially lethal complication, as such your pet will receive a course of antibiotics after surgery. Once home, exercise should be restricted for 4 weeks to allow healing and firm attachment of the lead to the heart. It is recommended to prevent your dog from activities that over-stretch the neck such as jumping up, going up and down the stairs or playing madly. Due to the position of the pacemaker and lead, your pet should wear a harness rather than a collar to avoid the risk of damaging the pacemaker. The sutures and bandage can be removed by your Vet around 10 days after surgery.
Your pet will need to return for pacemaker checks. These visits make sure the pacemaker is working correctly, monitor the battery life and ensure the pacemaker settings are optimised to meet the individual needs of your pet and maximise battery life.
The first programming check is due 1 months after surgery, this is the most important check as it is the first opportunity to check the pacemaker correct function and optimise the settings. After that, a programming check is required annually.
Should your dog outlive the battery life of the pacemaker (which only happens in very young dogs requiring pacemaker implantation), the battery can be replaced. This will involve a short operation to remove the old pacemaker and attach a new one to the existing lead.
Pacemaker battery. Modern pacemakers are small and light.
Radiograph after pacemaker implantation in a cat. The battery is at the level of the abdomen with the lead attached to the outside of the heart.
Radiograph after pacemaker implantation in a dog. The battery is at the level of the neck with the lead fitted through a vein reaching the right ventricle.
Patent Ductus Arteriosus (PDA)
PDA is one of the most common congenital heart conditions seen in young animals. It is more common in some breeds including the CKCS, Bichon, Chihuahua, Cocker Spaniel and German Shepherd dogs. Females are more commonly affected than males.
In patent ductus arteriosus (PDA) the vessel (ductus arteriosus) which connects the aorta and pulmonary artery during the foetal life fails to close after birth.
Uncorrected, a PDA leads to progressive heart enlargement and heart failure with lung congestion. If left untreated approximately 50% of dogs with a PDA die in the first year of life.
Your pet will typically have a loud murmur diagnosed as a puppy, although sometimes the PDA is not detected until they are much older and they may show signs of breathlessness and coughing. Before recommending PDA occlusion, a thorough ultrasound scan by a Specialist Cardiologist is necessary to check for signs of heart enlargement and to assess the degree to which heart function is reduced. This also enables the cardiologist to measure the size of the PDA in order to select the size of the occluder device required and provides an opportunity to double check for any other concurrent defects.
Interventional closure of the duct can be achieved with a canine specifically designed device made of a nitinol mesh (Amplatz canine ductal occluder - ACDO). Access is through the femoral artery and we use catheters and guidewires to advance to the level of the PDA. Once the angiography has been performed and the measurements confirmed the appropriate size of device will be chosen. The Amplatz can then be deployed to occlude from the inside the PDA and prevent flow through it. The device will remain in place for the dog’s life and will be visible on a chest radiograph.
The hospitalisation time only involves an overnight stay following the procedure, pets experience only minimal pain and much lower side effects compared to traditional surgery.
Closure of the PDA by a catheter-based technique is a highly successful and worthwhile procedure. The prognosis is excellent with a normal life expectancy when there is no/little heart enlargement or no evidence of congestive failure, especially when the procedure is performed in puppies. However, in older dogs if there is already severe heart dilation or lung congestion then a return to normal heart function is not always possible.
A follow-up scan by a cardiologist following surgery is important to check for the presence of residual flow through the ductus and assess heart size and function.
Pulmonic stenosis is one of the most common congenital heart conditions seen in young animals. It is the failure of the pulmonic valve to form and open fully. As a result, the blood flows through a narrowed exit and this obstruction causes the right side of the heart to become thicker. Some dogs will show clinical signs (weakness/collapse on exertion) and can lead with time to heart failure.
Balloon Valvuloplasty is performed in patients where moderate/severe pulmonic stenosis is diagnosed as we know dogs with severe forms of the disease will have a worse outcome if the procedure is not performed. Before recommending balloon dilatation, a thorough ultrasound scan by a Specialist Cardiologist is needed. The ultrasound is necessary to check the position of the stenosis, the severity of the stenosis, the extent to which heart function is reduced and to obtain measurements that will assist in determining which size of balloon catheter is required. The scan will also allow an opportunity to double-check for any other concurrent defects or suspect an abnormal coronary artery that would preclude such surgery. Some dogs (especially brachycephalic breeds) might need a coronary angiography prior to this procedure to make sure coronary anomalies are not present.
The procedure is performed accessing the heart via the jugular vein where catheters and guidewires are used to advance through the right atrium and ventricle to the stenotic valve. Once the angiography has been performed and the valve measured an appropriately sized balloon catheter is selected. This is then inserted to the level of the pulmonic valve and rapidly inflated and deflated multiple times to widen the stenosis. Great care needs to be taken at this time as inflating the balloon completely blocks the flow of blood out of the heart to the lungs.
The hospitalisation time only involves an overnight stay following the procedure.
A follow-up scan by a Specialist Cardiologist will be performed the day after surgery to measure the degree of success of the procedure and repeated after few months to check the remodelling of the heart.