Interventional cardiology refers to a minimally invasive surgery sometimes described as a type of “key-hole” surgery where the heart is accessed via a blood vessel. Special types of x-ray imaging known as fluoroscopy and angiography are used to guide the surgical procedure.
The main conditions that are treated by cardiac interventions are pulmonic stenosis, patent ductus arteriosus and abnormally slow heart rhythms that require a pacemaker to be implanted.
What is pulmonic stenosis and how is it treated?
Pulmonic stenosis is a type of congenital heart disease (a condition that the animal is born with) that occurs due to an abnormal pulmonic valve. The abnormal valve results in partial obstruction to the flow of blood and subsequently increases the workload of the right side of the heart. Over time this can lead to reduced ability to exercise, weakness, collapsing episodes and eventually heart failure.
A consultation, physical examination and ultrasound of the heart (echocardiography) is performed initially to assess whether pulmonic stenosis is present, the severity of the condition and whether other heart abnormalities are present that may interfere with surgery. In moderate and severe cases, a balloon valvuloplasty can be performed to help alleviate the obstruction. This procedure involves a special “balloon” catheter which is guided from a vein in the neck into the narrowed pulmonic valve. Once the catheter is in the correct place the balloon is inflated to stretch the valve and improve blood flow. The balloon is then removed and scan is performed two weeks after surgery to assess how successful the surgery has been. Patients with pulmonic stenosis benefit from tablets called beta blockers usually for at least 4 weeks prior to surgery and most patients will remain on this medication after the surgery has been performed.
What is a PDA and how is it treated?
Patent Ductus Arteriosus (PDA) is a persistent communication that remains after birth between the aorta and the pulmonary artery (the two major blood vessels that leave the left and right side of the heart respectively). This vessel should close at birth to stop blood being able to flow between the aorta and pulmonary artery but remains open in some animals. This causes an excessive amount of blood to flow into the left-side of the heart and results in the heart becoming severely enlarged. If left untreated, these patients will go on to develop severe heart failure. Many patients with a PDA show no clinical signs other than a loud heart murmur but some will become lethargic, reluctant to exercise and breathless, particularly if heart failure develops.
A thorough consultation, physical examination and echocardiography is done to assess the heart size and function and to definitively diagnose a PDA. The main surgical procedure that is performed involves the placement of a special device within the PDA, known as an Amplatz Canine Duct Occluder. This is done by passing a catheter into the main artery within the hind leg (the femoral artery) and “plugging” the PDA with the device, stopping the flow of blood across the PDA.
A repeat ultrasound scan is performed after surgery to ensure that the PDA has been successfully occluded. The success rates of this type of surgery are excellent if the patient has no signs of heart failure and go on to have a normal overall life expectancy.
For patients that are too small to undergo placement of the Amplatz Canine Duct Occluder, there is the option to surgically ligate the PDA. This is a more invasive but highly effective option to resolve PDA and has resulted in many patients being successfully treated.
A pacemaker refers to an external electronic device that is used to maintain the heart rate. In dogs and cats, a pacemaker is usually placed when there are abnormally slow heart rates that cause a reduction in the amount of blood flowing around the body resulting in episodes of collapse and fainting. A pacemaker monitors the heartbeat and will stimulate the heart to beat if the heart rate severely drops.
Certain types of pacemaker can also detect periods of exercise and stimulate the heart rate to increase during these periods. This is known as a rate-responsive pacemaker. Most pacemakers are set to have a heart rate range of 60 to 160 beats per minute.
The initial steps in deciding whether or not a pacemaker is required for your pet is to have a consultation including a clinical examination, echocardiography and an ECG (electrocardiography) which assesses the heart’s electrical activity. Other diagnostic tests that may be needed include bloodwork, chest x-rays and a Holter ECG, which is a monitor that is fitted to your pet over a longer period of time to monitor the heart rate and rhythm.
In dogs, the pacemaker itself is surgically placed under the skin at the side of the neck. A pacing lead is inserted into the heart via a catheter through the main blood vessels in the neck (the Jugular vein) and into the right side of the heart. The pacing lead then stays within the heart and is attached to the pacemaker in the neck, allowing it to deliver the electrical “spark” if the pacemaker detects that the heart rate is too slow to ensure the heart continues to beat.
After the pacemaker has been fitted, your pet will need to return regularly in order to perform a series of checks on the pacemaker and ascertain that it is working properly.