Key Points
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The best candidate for cryosurgery is a patient with refractory drug-sustained ventricular tachycardia (VT) from a left anterior aneurysm more than 2 months after a myocardial infarction, especially if the patient needs coronary artery bypass grafting (CABG) and ventricular restoration.
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Cryosurgery for VT can be performed visually with the same results as map-guided procedures.
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Large encircling cryotherapy is a simple, fast, easy to learn, and reproducible technique. Cryolesions should always be applied under cardioplegic arrest.
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Postoperative electrophysiologic study (EPS) is mandatory. Should a sustained VT remain inducible, an implantable cardioverter-defibrillator (ICD) must be implanted before discharge.
Historical Background
The first preoperative use of cryotherapy for ventricular tachycardia (VT) suppression was reported by Gallagher in 1978. The patient with diagnosed scleroderma presented with recurrent VT. During surgery, after localization of the site of origin of VT on the right ventricle by epicardial mapping, the abnormal focus of myocardium was frozen at −60°C and the patient remained free from VT originating from this site. Camm et al. reported a similar case soon after in 1979. After those two initial cases of surgical treatment of VT unrelated to ischemic heart disease, one had to wait until 1983 to read the first report of an ischemic VT cryoablation. Then the use of cryo for ablation of VT rapidly increased. Two schools emerged: the first one relied on intraoperative mapping and localized or regional ablative procedures, where cryotherapy was used as an adjunct to endocardial resection or alone ; the second one promoted an empirical encircling endocardial cryoablation of the entire visible endocardial scar and rapidly breached free from mapping.
Today, the landscape is profoundly altered by the widespread use of implantable cardioverter-defibrillator (ICD) and the huge advances in endocardial catheter ablation techniques. Most, if not all, nonischemic VTs are treated by radiofrequency or cryocatheter ablation. The use of cryosurgery for this indication remains confidential and tends to be less invasive. This considerable evolution lead Dr. Cox to write in 2004, “The only remaining viable surgical procedure[s] for cardiac arrhythmias [is] the Dor procedure for ischemic VT.” Even now, postinfarction recurrent VT has begun to be considered for catheter-based ablation. Nevertheless, in patients with postinfarction aneurysm and recurrent VT, myocardial revascularisation combined with aneurysm resection and VT cryoablation remains the only curative procedure addressing all the aspects of the disease in one setting.
Rationale for Using Cryoablation
Cryolesion results in a fibrous scar unable to promote or propagate electrical impulse, with a sharp delineation from adjacent normal myocardium. It fulfills six main criteria defined by Gallagher et al. to characterize an ideal technique for ablation:
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It preserves the structural integrity of the tissues undergoing ablation. Collagenous structure remains unaltered by the procedure and the following fibrous scar does not show tendency to dilate or rupture.
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It has minimal effect on normal structure and function. Cryosurgery can be applied on the base of mitral papillary muscle without subsequent massive mitral insufficiency, and it does not impair per se the left ventricular function.
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It creates a homogeneous lesion that is itself nonarrhythmogenic. This is the main strength of cryosurgery and has been demonstrated by many experimental works, as in Klein et al.’s report.
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It can be used initially in a reversible manner. An application from 0°C to −10°C for 10 to 15 seconds will temporarily stop myocardial conduction. After thawing, electrophysiologic properties are restored. This property has been used for the so-called ice-mapping or cryomapping in various arrhythmias.
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It allows continuous assessment of the ablation. Temperature is monitored during all the procedures. The diameter and depth of the cryolesion can be modulated by the size and shape of the cryoprobe, the tank pressure within the nitrous oxide delivery line, the temperature and duration of application, and the myocardial temperature.
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It can be rapidly used. Available cryothermia units are easy to handle and have a fast implementation. Duration of cryoapplication itself never extends 30 minutes.
When considering VT surgery, another advantage is the fact that cryotherapy can be applied alone, without the need for endocardial resection. This leaves more room and makes ventricular closure easier. Furthermore, dangers like septal perforation during endocardiectomy can be avoided. Although there are advantages of cryoablation over subendocardial resection, there are also some limitations: the depth of cryolesion is difficult to assess especially when facing thick myocardium ; the risk for complete heart block if cryo is applied too high and too close from the aortic annulus; and finally, the risk for a thrombosis in case of involvement of the coronary artery.
Cryoablation Technique
Cryoablation can be used in addition to another procedure. In this configuration, it is used at the periphery of the zone of subendocardial resection as in the Dor procedure, or it allows for the treatment of areas like mitral papillary muscle, which is crucial when facing a posterior aneurysm.
Cryoablation can also be used alone. Previously, it had been used with mapping in some reports, but it is now used more frequently without the need for mapping according to the methodology that Guiraudon et al. described.
After an initial period of map-guided procedures, we turned to large encircling cryoablation without mapping. The two main reasons to abandon mapping was that our rate of successful mapping has never reached 100%, and that in most patients with anterior myocardial infarction (MI), the earliest activation or cryotermination site was located by mapping within the area of the visible scar tissue. Furthermore, the fact that Takur et al. did not find any significant difference between patients operated on with and without mapping in their series comforted us in the way of visually guided large encircling cryoablation.
How to Do It
This chapter describes herein how to perform a procedure with large encircling cryoablation in a typical case of documented recurrent VT in a patient with a left ventricular aneurysm after anterior MI. This procedure has been previously described, but some refinements have been added.
After median sternotomy, internal mammary arteries and saphenous grafts are harvested if required. Then the pericardium is entered and adhesions are gently freed on the anterior and right aspect of the heart. Cardiopulmonary bypass is instituted with an aortic and two venous cannulas. Left venting is slightly pushed on the left atrium, and no attempt to put it on the left ventricle is done until the cavity has been checked for thrombus deposition. Normothermic cardiopulmonary bypass is now preferred, and after aortic cross-clamping, cold blood cardioplegia is used to arrest the heart. Reinfusions are performed every 20 minutes. Distal anastomoses are first performed when required; then the left ventricle is opened through the scar in a usual fashion. Trombus, if present, is carefully removed, and the cavity is explored to spot the borderzone between normal and scarred myocardium ( Figure 20–1 ). Then cryoablation is performed with a Frigitronics cryosurgical system CCS 100 with a 15-mm diameter flat-face curved probe (CooperSurgical, Shelton, CT). Points of cryolesion are applied 1.5 cm (which corresponds to the diameter of the probe) outside the area of the visible scar, clockwise, in a circular way starting from the superior edge of the ventriculotomy. Points are edge to edge or overlapping ( Figures 20–2 to 20–4 ). In the septum, where the exact delineation of the scar is more difficult, a second row is usually applied. Care is taken to avoid ablation in the upper part of the septum near its membranous portion, which can cause a His bundle block. It is important not to leave a gap between two points, especially in areas with thick trabeculations where overlapping is mandatory to avoid discontinuity. Usually, 11 to 12 points are applied at a mean temperature of −60°C during 2 minutes. During the defrost maneuver, room temperature saline is applied on the tip of the cryoprobe to fasten thawing and avoid sticking. This allows spending no more than 10 seconds between two points. As soon as the last point is achieved, the aorta is unclamped while strong suction is applied on the aortic vent. Closure of the aneurysm is then undertaken either by linear closure or by patch-plasty repair. Careful deairing is performed before releasing the heart onto position in the pericardial cavity. After surgery, patients are evaluated with an electrophysiologic study, the protocol of which has been previously described. In brief, the stimulation protocol (identical to the preoperative one) consisted one to three ventricular premature beats delivered with increasing prematurity on a 500-millisecond basic cycle length. Should a sustained VT (>30 seconds) be inducible or recorded on postoperative 24-hour Holter electrocardiogram, an ICD would now be considered before discharge. Patients are placed on warfarin and a 200-mg daily regimen of amiodarone for 3 months.
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