Roberto De Ponti, “Cryothermal Energy Ablation Of Cardiac Arrhythmias 2005:
State Of The Art”
18
Accessory pathways. In Table 1, published data on cryothermal ablation of anteroseptal
(parahissian) and midseptal accessory pathways are reported17,19,24-29. As shown, this technique
in anterospetal and midseptal areas, both at high risk of complete permanent atrioventricular
block when standard radiofrequency energy in performed, is highly safe and successful. In the
larger series, success rate is above 90%. Although transient modifications of the normal
atrioventricular nodal conduction pathways are observed during cooling, no permanent
modifications is observed with the only exception of right bundle branch block in 2 cases in a
single centre. In fact, immediate discontinuation of cryothermal energy application at any
temperature upon observation of modification of conduction over normal pathways results in
return to baseline condition, soon after discontinuation. Resumption of accessory pathway
conduction with palpitation recurrences may occur in the follow up to 20%, but, especially in
young healthy individual, a recurrence is by far more acceptable than permanent complete
atrioventricular block requiring pacing, which was invariably the case in many series of
radiofrequency ablation of these pathways. In our experience, we have treated 18 patients with
anteroseptal or midseptal accessory pathways, so far, age ranging 11-51 years. No patient was
excluded from the study for proximity of the accessory pathway to the normal conduction
pathways (Figure 3). Successful ablation was obtained in all, but 1 pediatric and asymptomatic
patient, in whom conduction properties over the accessory pathway indicated ablation, which
was eventually postponed. Cryoadherence effect proved very useful in every case, but especially
when energy delivery was performed during orthodromic atrioventricular tachycardia, to better
visualize the His bundle electrogram and to monitor conduction over normal pathways. No
complication or palpitation recurrences were observed during a 17±10 month follow-up. In
approaching anteroseptal and midseptal accessory pathways, instead of performing
“cryomapping” at -30°C in the selected site, we found it useful to test cryothermal energy
applications with a step-by-step method to decrease temperature. In fact, in the most suitable site
with the best contact (sometimes, a superior vena cava approach via a subclavian or a brachial
vein is useful to stabilize contact), test applications are applied for 30 s, initially with a
temperature of -30°C. If this test application is successful with no modification of normal
conduction, then transition to ablation at -75°C up to 480 s is made. If the test application is
unsuccessful, after re-warming, further 30s applications are tested, decreasing for each
application the temperature by 10°C every step, up to the last application at -70°C. This is
because we observed that the amount of cryothermal energy required for permanent ablation is
quite individual (ranging from an application of -40°C for 40s to an application of -75°C for
480 s) and limiting test applications to only -30°C may limit the applicability of cryoablation in
these patients. On the other hand, the use of cryothermal energy at temperatures lower than -30°
C should be considered safer than radiofrequency energy in these critical sites.
Cryoablation can be also successfully and safely used to ablate selected cases of
epicardial left-sided accessory pathways within the coronary sinus, well beyond the middle
cardiac vein, once attempts by using both transseptal and transaortic approach have failed20,30.
Similarly, safe and successful cryothermal energy ablation of permanent junctional reciprocating
tachycardia has been reported in children, in the midseptal region, at the coronary sinus os or in
the middle cardiac vein31.
The experience of cryoablation in unselected accessory pathways is more limited and less
satisfactory20. Of 51 accessory pathways with various locations, only 69% were successfully
ablated and this value is considerably lower than the one reported for radiofrequency ablation.
There are many possible explanations for this including the learning curve and the smaller size of
the lesion produced by cryoablation10. In any case, all the peculiarities of cryothermal energy,
which are optimal for septal ablation, are less important or even useless for ablation of accessory
pathways located elsewhere.
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(1): 12-24 (2005)