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went cryoablation using a 7F 4 mm-tipped catheter. At each prospective ablation site, cryo-mapping (−30◦C) which causes transient electrical dysfunction was ...
Journal of Interventional Cardiac Electrophysiology 10, 153–158, 2004  C 2004 Kluwer Academic Publishers. Manufactured in The Netherlands.

Clinical Usefulness of Cryomapping for Ablation of Tachycardias Involving Perinodal Tissue Tom Wong, Vias Markides, Nicholas S. Peters, and D. Wyn Davies St. Mary’s Hospital, London, UK

Abstract. Objectives: Radiofrequency (RF) ablation near the AV node carries a significant risk of AV block. We report our initial experience of using cryomapping function to aid the safe cryoablation close to the compact atrioventricular (AV) node. Methods: Five consecutive patients with para-Hisian accessory pathways (AP) (n = 2), or focal atrial tachycardia (AT) originating near the AV node (n = 3) underwent cryoablation using a 7F 4 mm-tipped catheter. At each prospective ablation site, cryo-mapping (−30◦ C) which causes transient electrical dysfunction was performed, and in the absence of AH interval prolongation, a full cryoablation (≤−70◦ C) was applied to the same site. Results: The AT foci, left in 2 patients and right in 1, and the APs were located 1.9 ± 3.0 mm and 4.5 ± 8.1 mm from the catheter recording the His deflection in two orthogonal radiographic projections. A His signal (0.18 ± 0.07 mV) was recorded at the site of successful cryoablation in both patients with AP and 1 with right AT. There was no change in AV nodal function during/after ablation. At each successful cryoablation site, interruption of target pathway/focus function was observed during cryo-mapping after 19.8 ± 12.4 s. Full cryoablation at sites where cryo-mapping had not caused an effect did not then produce any further electrophysiologic effect. All pathways and foci were ablated successfully without complications, using 3.2 ± 3.9 cryothermic applications alone in 4 patients, and after a supplementary RF ablation in 1. All patients remained free of arrhythmia at 15 ± 8 months follow-up. Conclusion: Cryomapping may help identify sites for safe and effective ablation of pathways and foci located near the AV node. Key Words. atrial tachycardia, para-Hisian accessory pathway, cryoablation

Introduction Radiofrequency (RF) catheter ablation has become the treatment of choice for the majority of supraventricular tachycardias. However, RF ablation near the compact atrioventricular (AV) node is associated with a significant risk of heart block [1,2]. Cryoablation allows the identification of transient electrophysiologic effects induced by reducing the temperature at the catheter tip in a con-

trolled fashion to −30◦ C (cryomapping) [3,4]. Thus if undesirable effects are seen during cryomapping, discontinuation of the application may prevent them from becoming permanent. Additionally, stability of the cryoablation catheter during freezing is ensured by the adhesion of the catheter tip to the endocardium. Also, the lesion created is more focus [5]. These favorable characteristics of cryoablation may encourage its use for ablating arrhythmias that involve a pathway/focus near the compact AV node.

Methods Patients We studied 5 consecutive patients who underwent cryo-ablative procedures between August 2000 and February 2003 for para-Hisian accessory pathways (AP, n = 2) or focal atrial tachycardia (AT, n = 3) originating close to the AV node. Three were male and their mean age was 41.4 ± 14.0 years. Their clinical characteristics are summarized in Table 1. Electrophysiologic Study and Mapping All procedures were performed under local anesthesia, in the fasting state and after obtaining written informed consent. A 12-lead surface ECG during pre-excitation or AT was obtained and analyzed. The P-wave morphology was assessed as previously described [6]. A conventional electrophysiologic study was performed using quadripolar catheters positioned in the high right atrium, right ventricular apex and the His bundle region, and a decapolar catheter positioned in the coronary sinus. In addition, a three-dimensional electroanatomical mapping system (CARTOTM , Biosense Webster, Inc. Address for correspondence: Dr. Tom Wong, MRCP, Waller Cardiology Department, St. Mary’s Hospital, Praed Street, London, W2 1NY, UK. E-mail: [email protected]

Received 30 July 2003; accepted 25 September 2003 153

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Table 1. Clinical characteristics

Pt. no.

Age (yrs)/ Gender

Structural heart disease

1 2 3 4 5

31/M 26/M 43/F 45/F 62/M

Nil Nil CAD Nil Severe MR & TR

Symptom

Duration of symptom (yrs)

Failed antiarrhythmic drugs (n)

Electrophysiologic diagnosis

Syncope & palpitation Pre-syncope & palpitation Dyspnoea & palpitation Lethargy & palpitation Dyspnoea & palpation

9 13 5 10 3

2 1 4 1 1

Pre-excited para-Hisian AP Concealed para-Hisian AP Left focal AT Left focal AT Right focal AT

CAD: coronary artery disease, MR: mitral regurgitation, TR: tricupid regurgitation, AP: accessory pathway, AT: Atrial tachycardia.

Diamond Bar, CA) was used in 1 patient (Patient 5) where distal coronary sinus electrode served as a reference. Atrio-ventricular nodal function was assessed before and after ablation during incremental atrial and ventricular pacing, and AH intervals were assessed before, during and after ablation. Accessory pathway conduction properties were also assessed by atrial and ventricular incremental pacing. Tachycardia was induced by programmed stimulation in patients in whom the arrhythmia was not incessant. The ventricular insertion of the AP in the patient with pre-excitation was mapped during atrial pacing. The site on the tricuspid annulus (TA) with the earliest ventricular electrogram preceding the delta wave and the shortest AV interval was identified. The atrial insertion of the concealed AP was located on the TA during orthodromic tachycardia by identifying the earliest atrial electrogram and the shortest VA interval. The AP was defined as para-Hisian when these location also recorded a His bundle potential of >0.1 mV. Standard criteria were used for the diagnosis of focal AT and its differentiation from re-entrant tachycardia [7,8]. Mapping of both atria was performed in all patients during AT to identify the earliest site of atrial activation.

Cryo-System c The cryoablation catheter used (Freezor, CryoCath Technologies Inc., Kirkland, Quebec, Canada) is a 7F 4-mm tipped quadripolar deflectable catheter with a closed electrode tip connected to a console and a conventional EP system. The refrigerant, liquid nitrous oxide is delivered from the console to the catheter tip where the liquid is vaporized. The transformation from liquid to gas at the catheter tip can reduce to temperature to ≤−70◦ C. The temperature can be accurately controlled by adjusting the flow of the refrigerant. Cryo-Mapping and Ablation Cryomapping at −30◦ C was applied at each target site for 40–60 s, during which the effects on

AV nodal and pathway/focus function were closely monitored. Provided that there was no AH prolongation during cryo-mapping, a full cryo-ablation at ≤−70◦ C was applied to the same site without re-warming for approximately 4 minutes. This allowed us to assess the safety prior to the placement of permanent lesion and also to investigate whether cryomapping can predict the outcome of full cryoablation. The procedure was considered successful if there was persistent loss of pathway/focus function during cryo-application that persisted after a 30 minute observation period and after re-testing with and without isoproterenol (AT) or adenosine (AP).

Fig. 1. Twelve-lead ECG showing (A) pre-excited QRS complexes in Patient 1 with negative delta-wave in aVR and aVL, iso-electric in V1 and V2, and positive in other leads; (B) during AT the P-waves in lead I, aVL and V1, were negative, iso-electric or biphasic with an initial downward deflection in both left AT (LAT) cases contrasting to predominantly positive or biphasic with initial upward deflection in the right AT (RAT) case.

Perinodal Cryothermic Mapping and Ablation

Follow-Up No anti-arrhythmic drug was restarted after ablation and all patients were followed-up in the out-patient clinic. Arrhythmia recurrence was accessed by symptoms, 12-lead ECGs and 24-hour Holter monitoring.

Results Electrocardiogram Twelve-lead ECGs during sinus rhythm revealed pre-excited QRS complexes in Patient 1 (Fig. 1A). The P-wave durations recorded during AT were shorter than that in sinus rhythm (457.3 ± 6.1 vs. 115.3 ± 8.1 ms, p = 0.0004), and the P-wave morphologies were summarized in Fig. 1B. Electrophysiologic Study and Mapping Tachycardia was incessant in Patient 5 and inducible in the remaining 4 patients. Mapping was performed during tachycardia except in Patient 1 in whom it was performed during atrial pacing. The electrophysiologic characteristics of successful ablation sites were summarized in Table 2. Clear His potentials of 0.20, 0.23 and 0.1 mV were recorded at those sites in the two patients with

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APs and one with AT originated from the right atrium (Fig. 2).

Cryo-Mapping and Ablation All APs and AT foci were ablated successfully without complications, using cryothermy alone in 4 patients and after supplementary RF ablation in 1. Successful ablation sites were located 1.9 ± 3.0 mm and 4.5 ± 8.1 mm from the His catheter in two orthogonal radiographic projections. Cryomapping at all 4 successful sites resulted in loss of pathway/focus function after 15, 10, 38 and 16 s respectively. No electrophysiologic effect was observed during cryomapping at the ineffective sites. In Patient 4 the tachycardia was nonsustained, nonetheless consistently initiated by 2 atrial extra-stimuli. In this case a single cryomapping terminated the AT after 2.8 s. The absolute catheter stability due to cryo-adhesive effect during freezing allowed the tachycardia initiation pacing manoeuvre to be repeated during the cryodelivery. The clinical tachycardia was re-initiated 3 times by this, the last time being 38 s into the cryomapping period. A full cryoablation was delivered at the same site without re-warming, rendering the tachycardia non-inducible.

Fig. 2. (A) Two fluoroscopic projections showing the site of successful cryoablation (CRYO) was close to the His catheter (HIS) in Patient 5. (B) Top panel showing before ablation there was AV nodal Wenkebach during AT (CL 380 ms), the earliest atrial activation (asterisk) was 83 ms before P-wave onset with a clear His potential (arrow head). Bottom panel showing during cryo-mapping at that site, termination of tachycardia (arrow) occurred after 16 s and was preceded by prolongation of tachycardia CL. CSd: distal coronary sinus; CSp: proximal coronary sinus; HISd: distal His; HISp: proximal His; HRA: high right atrium; LAO: left anterior oblique projection; MAPd: distal map; MAPp: proximal map; RAO: right anterior oblique projection.

Pre-excited para-Hisian AP Concealed para-Hisian AP Left focal AT Left focal AT Right focal AT

1

Isoproterenol Two atrial ES Spontaneous

Ventricular or atrial ES Ventricular ES

Mode of induction

360 408 380

330

320

CL (ms) Atrial pacing & pre-excitation Orthodromic tachycardia AT (intermittent) AT (intermittent) AT (incessant)

Rhythm

A — P-wave onset 86 ms A — P-wave onset 64 ms A — P-wave onset 83 ms

Peak-peak AV time 30 ms, V-delta onset 10 ms Peak-peak VA 0 ms

Successful site of ablation

Mapping

– 38 16

10

15

Loss of pathway/ focus during cryo-mapping (s)

10 1 1

1

3

Total no. of cryo-application

Cryoablation

A: atrial electrogram, AP: accessory pathway, AT: atrial tachycardia, AV: atrio-ventricular, CL: cycle length, ES: extra-stimulus/stimuli, V: ventricular electorgram.

3 4 5

2

Diagnosis

Pt no.

Tachycardia

Table 2. Tachycardia, mapping and ablation characteristics

38.9 4.8 4.6

4.2

14.2

Total duration of cryo-application (min)

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tively. The antegrade and retrograde AV conduction before and after ablation are shown in Table 3. The antegrade and retrograde AV nodal conduction was unaffected after cryoablation in all patients except in patient 1 where the AV node effective refractory period could not be measured with certainty before ablation because of the proximity of the AP to AV node.

Follow-Up After a mean duration of follow-up of 15.3 ± 8 (range 3.7–24.4) months, all patients were free from arrhythmic symptoms without drug therapy. Surface ECG showed normal PR intervals (161.0 ± 4.5 ms) and no return in delta in the patient who had pre-excited AP. Holter monitoring at follow-up did not show recurrent tachyarrhythmia in any of the patients.

Fig. 3. Electrograms in Patient 3 showing (A) at a typical unsuccessful cryoablation (CRYO) site where atrial electrogram was less early than (B) that at the successful radiofrequency (RF) ablation site where an atrial electrogram (asterisk) was 86 ms before P-wave onset. Abbreviations as in Figure 2.

Discussion Although successful RF ablation of APs and AT foci near the compact AV node has been reported [7–10], the risk of developing AV nodal conduction block during these procedures remains a concern [1,2]. The unique characteristics of cryothermic ablation may be helpful in such high risk cases. Our initial experience demonstrates the safe and effective ablation of pathways and foci near the AV node using a 7F 4 mm tipped percutaneous cryoablation catheter. Cryothermy has been used in surgical ablation in the past two decades. The reversible suppression of electrophysiologic function that has been observed at 0◦ C during open heart surgery [3] has also been recently reported using a percutaneous cryoablation system with the catheter tip temperature at around −30◦ C (cryomapping) [4]. The lower temperature required for this process with a percutaneous catheter system when compared with that required for surgical ablation, 0◦ C, is because of the warming effect of the circulatory blood. This unique property is particularly

In Patient 3, total 10 cryoablations preceded by cryomapping were applied at sites of early atrial activation (72.5 ± 4.1 (range 68–78) ms before Pwave onset) without any effect. A single RF application at a location with an even earlier atrial potential (86 ms before P-wave onset) terminated the tachycardia and rendered it non-inducible (Fig. 3). In total, 16 cryothermic applications were delivered, including the 4 successful ones. The mean number of cryo-applications was 3.2 ± 3.9 (range 1–10) and the mean duration of cryothermic applications was 13.6 ± 14.7 (range 4–38.8) min per patient. The total procedural and fluoroscopic durations including diagnostic study were 250 ± 99 (range 180 ± 420) and 48 ± 29 (range 24–74) min respectively.

AV Nodal Properties The AH intervals recorded before and after ablation were 103.2 ± 19.8 and 99.6 ± 20.9 ms respecTable 3. Atrio-ventricular conduction before and after ablation AH interval (ms)

AV block (ms)

VA block (ms)

Pt. no.

Pre-Abl

Post-Abl

Pre-Abl

Post-Abl

Pre-Abl

Post-Abl

1 2 3 4 5

78 100 120 92 126

76 90 128 90 114

220∗