Roberto De Ponti, “Cryothermal Energy Ablation Of Cardiac Arrhythmias 2005:
State Of The Art”
baseline conduction properties, with no permanent damage to normal conduction. Recently, it
has been demonstrated in a canine model10 that cryolesions are associated with significantly less
endothelial disruption and overlying thrombus formation as compared to lesion produced by
radiofrequency energy, regardless of the preventive use of aspirin. This characteristic could be
very important, especially when multiple and prolonged energy applications are required to treat
atrial arrhythmias in the left atrium. Unlike lesions produced by a hyperthermic injury,
cryolesions show both in open chest11 and closed chest10,12 models, a well demarcated border
zone and preservation of the extracellular collagen matrix with no collagen denaturation, nor
contracture related to hyperthermic effects. These histologic observations combine with the
clinical evidence that cryothermal energy application adjacent to coronary arteries, as well as in
venous vessels (coronary sinus, middle cardiac vein and pulmonary veins)12,13,14,15, does not
results in damage nor chronic stenosis of their lumen.
15
In the already mentioned study10, it has been pointed out that lesions by radiofrequency
energy have a comparable depth of those produce by cryoablation. Nevertheless, radiofrequency
energy ablation resulted in a highly significantly greater area and a nearly significantly larger
volume when compared to cryolesions. Moreover, colder temperatures were associated with
deeper lesions and greater area and volume were associated with use of 9 F as compared to 7 F
catheters. It is not clear why cryothermal energy produces a lesion with similar depth, but smaller
area and volume, when compared to the one produced by a “similar” radiofrequency energy
application. One plausible explanation could be the “cryoadherence” effect, which is a tight
adherence of the catheter tip to the adjacent tissue caused by cooling. Due to this effect, the
lesion produced is very focal, since the “brushing” of the tip electrode, usually observed during
radiofrequency ablation, is missing. On the other hand, the advantage of this effect is two-fold.
First, below the critical temperature of -20°C it allows good tip electrode to tissue contact,
which persists throughout the whole application and it is not dependent on the torsion/deflection
manoeuvres applied to the catheter. It is well known that a fixed and stable contact during the
whole application is essential, especially for ablation in proximity of critical areas, such as
atrioventricular node and His bundle. Second, the cryoadherence effect allows safe continuation
of the application, even when sudden changes in heart rhythm that usually displace the ablation
catheter (such as tachycardia termination or pacing) occur. Moreover, cryoadherence does not
compromise safety, since, upon discontinuation of cryothermal energy delivery, the defrost phase
is very fast (within 3 s) and the catheter can be immediately disengaged from the ablation
position.
Finally, another peculiarity of cryothermal energy is the complete absence of patient
symptoms in almost every case, in spite long-lasting applications. In our experience, we have
evaluated patient perceptions during cryothermal energy application in a series of non-sedated
cases. In almost all cases, the absolute absence of perception was demonstrated by the fact that
the patient was unable to tell when the application was started and discontinued. Only in some
cases, when multiple and prolonged applications are delivered in the left heart, a light sense of
cold or headache is perceived as minor discomfort. Although the full explanation of the absence
of symptoms is not completely clear, this characteristic can be particularly useful in young as
well as in paediatric patients.
Clinical use in ablation of cardiac arrhythmias
Over the last five yeas, the world-wide experience in catheter ablation of cardiac
arrhythmias by using cryothermal energy has increased unabated. Based on this experience,
cryoablation should not be viewed as a replacement for radiofrequency energy, which will
continue to be the method of choice in many clinical situations. Nevertheless, ablation by
cryothermal energy should be rather considered as a useful addition to the electrophysiologist’s
armamentarium. In fact, different types of arrhythmias are now successfully treated by
cryoablation and in some cases, especially in proximity to normal conduction pathways,
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(1): 12-24 (2005)