Alcohol Septal Ablation For Hypertrophic Cardiomyopathy: Procedure, Complications, And Recovery

Hypertrophic cardiomyopathy (HCM) is the most common type of inherited heart disorder. In this condition, parts of the heart muscle become abnormally thick, making it harder for the heart to pump blood. In some cases, HCM can cause outflow tract obstruction, a condition in which the passage of the blood from the heart is limited or partially blocked. As a consequence, the patient might feel tired, dizzy, or experience chest pain and breathlessness. Patients who have outflow obstruction have a higher risk than other HCM patients of developing life-threatening complications like stroke, heart failure, and sudden cardiac death.

Treatment for obstructive hypertrophic cardiomyopathy  

The first line of treatment to alleviate symptoms and reduce the risk of complications is medication. While medication is effective for most of the patients, five to 10 percent either don't respond to medication or have serious adverse reactions. That calls for another approach, based on physically reducing a part of the heart called the septum. There are two options — an open-heart surgery called septal myectomy in which excess heart tissue is excised, or a non-surgical procedure called alcohol septal ablation.

However, as later data showed, applicability, effectiveness, and complications of this procedure were different than anticipated. The choice between ASA and septal myectomy is a complex medical decision, and multidisciplinary heart teams should make this assessment. The choice is, ultimately, often left to the patient. 

What is outflow tract obstruction and how does it happen in HCM patients?

Your heart is a muscular pump consisting of four chambers: two upper ones called atria, and two lower ones called the ventricles. The left and the right side of the heart are separated by a muscular wall called the septum. In two-thirds of HCM patients, the septum is the affected part, although any part of the left ventricle (the heart's main pumping chamber) can be involved. Other parts of the heart like the mitral valve (a valve between the left atrium and the left ventricle) or the right ventricle can also be abnormal.

Oxygenated blood is pumped from the left ventricle to the aorta, the main artery which carries blood to all of the organs and the cells in your body. Sometimes, the thickened septum can bulge into the left ventricle, just where the aortic valve is. The aortic valve is something like a gate between the left ventricle and the aorta, which directs the flow of blood. Thickening of the septum can lead to the narrowing of the passageway, essentially limiting or blocking the blood flow. This is called outflow tract obstruction. The left ventricle needs to pump harder to meet the body's demands. The patient might feel dizzy and exhausted because the body is not getting enough oxygen. 

What happens during the procedure?

You will also receive medications that prevent blood clotting, like heparin and aspirin, as well as a local anesthetic to your groin (that might need to be shaved prior to the procedure).

The doctor will make a small incision on your groin and insert a catheter — a plastic, flexible hollow tube — into the blood vessel. The tube is threaded all the way to your heart through the blood vessels. Echocardiogram (echo, heart ultrasound) and angiography (an imaging technique that uses X-rays to visualize blood vessels) are used to guide the catheter into the right position. A temporary pacemaker is inserted through the veins. 

When the balloon reaches the branch of the artery that feeds the septum, 1-4 mL of alcohol is injected. Correct identification of this specific blood vessel is the key to this procedure. The alcohol used is 96 percent ethanol, which is very toxic to the cells (for comparison, alcohol used to disinfect surfaces and kill bacteria and viruses is 80 percent). It causes the death of heart cells in the basal septum, the part where the thickening has happened. This might cause discomfort in your chest followed by a burning sensation lasting around one to two minutes.

What are the possible complications of alcohol septal ablation?

Most patients feel immediate relief after the procedure and the risk of death is low (up to four percent). Compared to myectomy, it's a simpler and cheaper procedure with a significantly shorter recovery time. However, ASA comes with its own sets of serious risks, and a much higher risk of needing re-intervention (in almost eight percent) and a permanent pacemaker.

Disruption of the conduction system

A network of specialized heart muscle cells sends electrical signals through the heart that cause contraction. This network initiates and maintains the regular heartbeat and it’s called the cardiac conduction system. The cells of the system are grouped into nodes that are connected by branches that together form an electrical path. Both permanent and transient disruptions of that path are known to happen during alcohol septal ablation. The reason for that is that the targeted blood vessel in which the alcohol is injected feeds parts of the conduction system as well, and not just the septum.

Known complications include:

• First degree AV (atrioventricular) block and RBB (right bundle branch) block. Both are common (happen in nearly half of patients), but transient and usually benign.
• Complete heart block. This is the most concerning complication of ASA due to its high incidence and the frequent need for a permanent pacemaker. It's a dangerous condition that can be fatal, and happens in 10 to 15 percent ASA patients, although some studies report the incidence being as high as 50 percent. It usually happens during or after the procedure, but examples of complete heart block that happened a week after the ASA have also been documented.

Ventricular arrhythmia (VA)

Ventricular arrhythmias are abnormal heartbeats caused by electrical impulses that originate from the ventricles. Patients with HCM are already at risk. The danger rises after ASA, especially during the first week after the procedure. One of the reasons is the scar tissue that forms after the targeted heart tissue dies. Certain types of ventricular arrhythmias, like ventricular fibrillation (or V-fib) are life-threatening conditions that require immediate medical attention. 

Damage of the blood vessels

• Tears of the vessels during catheterization leading to cardiac tamponade (accumulation of fluid around the heart)
• Spillover of alcohol to left coronary artery resulting in severe damage 
• Tears to the left coronary artery 

Others

• Infection
• Pulmonary embolism (blockage of arteries in the lungs, usually by a blood clot)

Recovery        

You should expect to stay in the cardiac intensive care unit for two to three days, if there are no complications. In the first few hours after the procedure, you will be asked to lay flat, without bending your legs, to prevent bleeding. The doctor will perform tests, like an echocardiogram (heart ultrasound), to see if the procedure was successful. Your medical team will give you detailed instructions to follow once you're released from the hospital. Most patients can return to light activities very soon.