Atrial fibrillation (AF), or an irregular heartbeat, is present in up to 2% of the population and in approximately 10% of those aged over 60y, making it by far the most common form of sustained abnormal heart rhythm (arrhythmia). Although AF is often considered to be innocuous, it is sometimes associated with serious morbidity due to its three detrimental sequelae:
- Palpitations, resulting in patient discomfort and anxiety,
- Loss of synchronous atrial then ventricular contraction, which compromises cardiac haemodynamics resulting in various degrees of ventricular dysfunction or congestive heart failure,
- Stasis of blood flow in the left atrium which increases the risk of thromboembolism and stroke.
Atrial fibrillation is classified into 4 categories which then help to decide the treatment strategy:
- Paroxysmal – meaning the AF is intermittent. These episodes are generally self-terminating and last <48h but can last up to 7 days.
- Persistent – these are episodes that last longer than 7 days or require termination by cardioversion (drugs or direct current).
- Long-standing persistent – episodes of AF that last longer than 1 year but where the aim is still to restore sinus rhythm.
- Permanent – in this case, we just accept that the AF cannot be cured and the aim of treatment shifts from controlling the rhythm to controlling the heart rate, as well as protecting against blood clot formation with the use of blood-thinning drugs.
There are various treatment options which your cardiologist will discuss with you, ranging from antiarrhythmic and anticoagulant tablets, to cardioversion, to catheter ablation or surgical ablation. The surgical options are all based on the work of Dr James Cox at Washington University in the 1980s, who identified the key role of macro-reentrant circuits in established AF, prior to the identification of focal triggers in and around the pulmonary veins some 11 years later. Dr Cox devised a maze-like series of lines of scar tissue placed around the left and right atria that were designed to form lines of permanent conduction block to interrupt these macro-reentrant circuits. The procedure became known as the Cox-Maze procedure and went through various refinements from the Maze I to the Maze III. The lines of scar tissue were initially made by cutting the atrial wall but this was complex and associated with an important risk of bleeding in the early post-op period. We now have alternative ways of forming lines of conduction block, such as freezing (cryothermy) or heating (radiofrequency), and this has led to the Cox-Maze IV. Similarly, we no longer need to perform a sternotomy to access the heart as this is considered very invasive but rather the operation can be performed through tiny incisions (minimally invasive). There are two surgical options for the treatment of stand-alone AF, namely a minimally invasive cryomaze or a totally thoracoscopic approach, and the differences between these will be detailed below. It will be interesting to see how this field pans out over the next few years.
Minimally invasive cryomaze
This procedure replicates the Cox Maze IV lesion set and is therefore likely to carry a higher success rate than the totally thoracoscopic approach, which is a more limited lesion set. The operation is performed through a 5-6cm mini-incision on the right side of the chest and uses the heart-lung machine (cardiopulmonary bypass). It involves freezing parts of the inside of both atria down to -150°C to create the scar tissue that precisely recreates the Maze IV lesion set. The left atrial appendage, an important source of blood clots in AF, is also excluded internally. Some of the latest US data published in The Annals of Thoracic Surgery from 2013 has shown a 94% success rate at 1 year on anti-arrhythmic drugs (87% off anti-arrhythmic drugs) (reference: Ann Thorac Surg. 2013 Sep;96(3):792-8). Hospital stay is about 5 days and the risks of the operation are very small but not zero.
Totally thoracoscopic approach
This is performed using three 1cm ports on each side of the chest and through one of these we use a HD video camera to visualise the heart. Bipolar radiofrequency is used to isolate the pulmonary veins and the posterior left atrium. It does not need cardiopulmonary bypass unlike the minimally invasive cryomaze procedure. The complete Cox Maze IV lesion set however cannot be formed and therefore the success rate is unlikely to be as high as the minimally invasive cryomaze, which is supported by data from the FAST trial which reported 66% success at one year for this procedure (reference: Circulation. 2012 Jan 3;125(1):23-30). There are groups reporting higher success rates. A clip can also be applied to the left atrial appendage to exclude it during the part of the procedure in the left chest. We don’t have any studies yet directly comparing the mini cryomaze to the totally thoracoscopic approach as both of these procedures are right at the forefront of cardiac surgery.
Three 1cm ports are used on each side of the chest for the totally thoracoscopic approach.