| Catheter ablation |
Catheter ablation is a procedure that uses radio-frequency energy or other sources to terminate or modify a faulty electrical pathway from sections of the heart of those who are prone to developing cardiac arrhythmias such as atrial fibrillation, atrial flutter and Wolff-Parkinson-White syndrome. If not controlled, such arrhythmias increase the risk of ventricular fibrillation and sudden cardiac arrest. The ablation procedure can be classified by energy source: radiofrequency ablation and cryoablation.
Catheter ablation may be recommended for a recurrent or persistent arrhythmia resulting in symptoms or other dysfunction. Atrial fibrillation frequently results from bursts of tachycardia that originate in muscle bundles extending from the atrium to the pulmonary veins.[1] Pulmonary vein isolation by transcatheter ablation can restore sinus rhythm.
Catheter ablation of most arrhythmias has a high success rate. Success rates for WPW syndrome have been as high as 95% [2] For Supraventricular tachycardia (SVT), single procedure success is 91% to 96% (95% Confidence Interval) and multiple procedure success is 92% to 97% (95% Confidence Interval).[3] For atrial flutter, single procedure success is 88% to 95% (95% Confidence Interval) and multiple procedure success is 95% to 99% (95% Confidence Interval). For automatic atrial tachycardias, the success rates are 70–90%. The potential complications include bleeding, blood clots, pericardial tamponade, and heart block, but these risks are very low, ranging from 2.6 to 3.2%.
For non-paroxysmal atrial fibrillation, a 2016 systematic review compared catheter ablation to heart rhythm drugs. After 12 months, participants receiving catheter ablation were more likely to be free of atrial fibrillation, and less likely to need cardioversion. However, the evidence quality ranged from moderate to very low[4] A 2006 study, including both paroxysmal and non-paroxysmal atrial fibrillation, found that the success rates are 28% for single procedures. Often, several procedures are needed to raise the success rate to a 70–80% range.[5] One reason for this may be that once the heart has undergone atrial remodeling as in the case of chronic atrial fibrillation patients, largely 50 and older, it is much more difficult to correct the 'bad' electrical pathways. Young people with AF with paroxysmal, or intermittent, AF therefore have an increased chance of success with an ablation since their heart has not undergone atrial remodeling yet. Several experienced teams of electrophysiologists in US heart centers claim they can achieve up to a 75% success rate.
Pulmonary vein isolation has been found to be more effective than optimized antiarrhythmic drug therapy for improving quality of life at 12 months after treatment.[6]
Catheter ablation has been found to improve mental health outcomes in individuals with symptomatic atrial fibrillation.[7]
A 2018 study showed efficacy of cardiac ablation for treatment of Premature Ventricular Contraction as 94.1%.[8]
Catheter ablation is usually performed by an electrophysiologist (a specially trained cardiologist) in a cath lab.
Catheter ablation procedure involves advancing several flexible catheters into the patient's blood vessels, usually either in the femoral vein, internal jugular vein, or subclavian vein. The catheters are then advanced towards the heart. The catheters have electrodes at the tips that can measure the electrical signals from the heart. These electrodes create a map of the abnormal pathways causing arrhythmias. Then, the electrophysiologist uses the map to identify areas that abnormal heart rhythms originate.[9]
Once the abnormal areas are located, catheters are used to deliver energy via local heating or freezing to ablate (destroy) the abnormal tissue that is causing the arrhythmia. The energy is applied cautiously to avoid damaging healthy heart tissue. Originally, a DC impulse was used to create lesions in the intra-cardiac conduction system.[10] However, due to a high incidence of complications, widespread use was never achieved.
In contrast to the thermal methods (extreme heat or cold) electroporation is being used and evaluated as a means of killing very small areas of heart muscle. The cardiac catheter delivers trains of high-voltage ultra-rapid electrical pulses that form irreversible pores in cell membranes, resulting in cell death of cardiac muscle, while not killing adjacent tissues (esophagus and phrenic nerve).[11] It is thought to allow better selectivity than the previous thermal techniques, which used heat or cold to kill larger volumes of muscle.[12]
One type of catheter ablation is pulmonary vein isolation, where the ablation is done in the left atrium in the area where the 4 pulmonary veins connect.[13] [14] Radiofrequency ablation for atrial fibrillation can be unipolar (one electrode) or bipolar (two electrodes).[15] Although bipolar can be more successful, it is technically more difficult, resulting in unipolar being used more often. But bipolar is more effective in preventing recurrent atrial arrhythmias.[16]
During the procedure, the patient's heart rhythm is monitored continuously. The electrophysiologist can observe changes to the patient's cardiac electrical activity to determine the success of the ablation. If the cardiac rhythm shows no abnormal signals or arrhythmias, the catheters are withdrawn from the heart and the incision is closed.
After catheter ablation the patients are moved to a cardiac recovery unit, intensive care unit, or cardiovascular intensive care unit where they are not allowed to move for 4–6 hours. Minimizing movement helps prevent bleeding from the site of catheter insertion. Some people have to stay overnight for observation, some need to stay much longer and others are able to go home on the same day. This all depends on the problem, the length of the operation and whether or not general anaesthetic was used.
Recurrence of atrial fibrillation within three months of an ablation is seen in most patients, but many of those patients become free of atrial fibrillation in the long term.[17] For this reason the first three months after an ablation are described as the "blanking period," during which no further intervention is to be attempted. Recurrence during the nine months following the blanking period, occurs in 25% to 40% of patients, the variability greatly affected by obesity and the severity of atrial fibrillation before the ablation.
Some potential complications associated with the procedure include:[18]
Patients may also experience a return of the arrhythmia after the procedure, requiring them to undergo further treatment. However, in general this procedure is considered a safe, effective, and minimally invasive method to treat arrhythmias. Studies have shown that the overall complication rate of cardiac ablation procedures is about 6%.