Bidirectional Cavotricuspid Isthmus Conduction Block Research Articles

AB-452675-4 CORONARY ARTERIAL SPASM DURING CAVO-TRICUSPID ISTHMUS ABLATION WITH A NOVEL FOCAL PULSED FIELD ABLATION CATHETER: FINDINGS FROM CORONARY ANGIOGRAPHY AND FRACTIONAL FLOW RESERVE MEASUREMENTS

Pulsed field ablation (PFA) has been shown to avoid esophageal damage, PV stenosis and permanent phrenic nerve paralysis. But not studied in these trials was ablation of the cavo-tricuspid isthmus (CTI), a not uncommon adjunct target for ablation during pulmonary vein isolation (PVI) procedures. Indeed, recent studies demonstrated that when PFA is performed adjacent to a coronary artery, there is a susceptibility for vasospasm: in a study of right coronary artery (RCA) angiography during PFA of the cavo-tricuspid isthmus (CTI), there was universally severe RCA spasm, albeit subclinical. However, these studies were performed with a pentaspline PFA catheter designed to create a broad electrical field, not with a focal spot ablation catheter. To evaluate the potential for PFA to cause coronary spasm during CTI ablation, but using a focal PFA catheter. As part of a clinical trial of persistent AF ablation (PersAFOne 3, NCT05272852), after PVI and posterior wall ablation using a 12F commercial pentaspline PFA catheter (Farawave, BSC Inc.), CTI ablation was performed using an investigational 8F deflectable focal catheter (Farapoint, BSC Inc.). PFA was performed at 2kV (2 x 2.5 sec applications per site) with fluoroscopy and ICE guidance. Coronary angiography of the RCA with FFR measurement (Abbott PressureWire X) was performed before, during and after PFA at each application site. Spasm was categorized as mild (<50%), moderate (50-90%) or severe (>90%). At a single center, PFA of the CTI was performed in 8 patients. Bidirectional CTI conduction block was achieved in all patients after a mean of 13.3 lesions/pt (range 8-18). One patient had a left dominant coronary arterial system, and a de minimis RCA; of the remaining, 6 of 7 patients developed moderate (n=5) to severe (n=1) spasm as determined by both angiography and FFR (mean pressure differential 0.60, range 0.31-0.78 among patients developing spasm). There were no EKG changes and no symptoms (albeit sedated patients). The mean time for spasm resolution was 13.8 min. In an additional patient, intracoronary NTG pretreatment (1 mg) was administered before PFA lesions were delivered to the CTI: no coronary spasm was provoked. Focal PFA to the CTI provokes subclinical coronary vasospasm when delivered adjacent to the RCA. Additional investigation is necessary to determine the optimal NTG dosing strategy to prevent this phenomenon.

Simultaneous pulmonary vein cryoablation and cavotricuspid isthmus radiofrequency ablation in patients with combined atrial fibrillation and typical atrial flutter

Pulmonary vein isolation (PVI) using cryoballoon (CB) technique and cavotricuspid isthmus (CTI) ablation using radiofrequency (RF) are established interventions for drug-resistant atrial fibrillation (AF) and typical atrial flutter (AFL). Twelve patients with a mean age of 62±12years underwent simultaneous delivery of RF energy at the CTI during CB applications at the PV ostia. Pulmonary vein isolation was achieved in all PVs and sustained bidirectional CTI conduction block obtained in all patients. The reported ablation protocol of combined paroxysmal AF and typical AFL did not result in prolongation of the procedure duration or in prolonged radiation exposure when compared to CB-PVI alone. No interferences between both ablation energy systems were observed. These preliminary results suggest that combined paroxysmal AF and typical AFL can be successfully and safely ablated using hybrid energy sources with simultaneous CTI ablation using RF during CB applications at the PV ostia.

Initial clinical experience with a novel visualization and virtual electrode radiofrequency ablation catheter to treat atrial flutter

Linear ablation lesions are used to treat a variety of cardiac arrhythmias. However, successful long-term outcome is hampered by both the uncertainty of catheter-tissue contact for any individual lesion and the difficulty in ensuring point-to-point lesion contiguity. A novel virtual electrode radiofrequency ablation catheter equipped with an endoscope to directly visualize the target tissue was used to ensure tissue contact and lesion contiguity along the cavotricuspid isthmus (CTI) to treat typical atrial flutter. In this feasibility study of five patients with drug-resistant CTI-dependent atrial flutter, catheter ablation was performed using the visualization virtual electrode radiofrequency ablation catheter. After standard femoral access, the ablation catheter was advanced to the tricuspid annulus under fluoroscopic and intracardiac echocardiography guidance. In three of five patients, the ablation procedure was performed during atrial flutter; the other two ablations were during coronary sinus pacing. Conversion to sinus rhythm was noted after the delivery of 12 ± 7 lesions. Bidirectional CTI conduction block was successfully achieved in all patients. Initial, transient CTI block was first observed after delivering 19 ± 13 lesions; ultimately, 34 ± 18 lesions were required to achieve permanent bidirectional CTI block. The mean ablation and procedure times were 72 ± 42 and 151 ± 17 minutes. The mean fluoroscopy times for the ablation alone and the entire procedure were 13 ± 8 and 17 ± 7 minutes, respectively. This study introduces the clinical feasibility of a novel paradigm for contiguous linear ablation: virtual electrode ablation under direct endoscopic visualization.

Not so innocent bystander(s)

A patient with atrial flutter, intermittent non-sustained wide complex tachycardia and 1:1 AV conduction is reported. Electrophysiology testing showed counterclockwise isthmus-dependent right atrial flutter with conduction via the AV node and an innocent bystander left lateral accessory pathway. This explained the observed intermittent wide complex tachycardia. After successful bidirectional cavotricuspid isthmus conduction block, a sustained wide complex tachycardia with identical counterclockwise right atrial activation and rate occurred. This was due to antidromic AV re-entrant tachycardia with innocent bystander activation of the right atrium mimicking atrial flutter. Accessory pathway ablation effectively stopped tachycardia.

Successful Catheter Ablation of Typical Atrial Flutter in a Patient with a Long Vertical and Diverticulum‐Like Cavotricuspid Isthmus

A long vertical vestibule with a diverticulum-like morphology of cavotricuspid isthmus (CTI) was demonstrated by right atrial angiogram in a 47-year-old male patient in whom his typical atrial flutter was difficult to be ablated. Compatible with the right atrial angiography, the diverticulum-like CTI with a long vertical vestibule, pouch-like recess, and a long transverse posterior component was also demonstrated on volume-rendering reconstruction computed tomography and the virtual endoscopy showed prominent trabeculation inside the diverticulum-like part of CTI. The bidirectional CTI conduction block was successfully achieved after ablating along the CTI guided by the right atrial angiography.

Transvenous catheter–based microwave ablation for atrial flutter

We report a case of successful transvenous, catheter-based, cavotricuspid isthmus ablation for treatment of atrial flutter using microwave energy. Microwave energy was delivered at 900–930 MHz using 21 W of power. Bidirectional cavotricuspid isthmus conduction block was achieved by microwave ablation without any patient discomfort or complication during the procedure. Our initial experience suggests that transcatheter microwave ablation is feasible for the cure of typical atrial flutter.

Single cryothermia applications of less than five minutes produce permanent cavotricuspid isthmus block in humans

The aim of this study was to compare single-3-minute (single-3) with double-3-minute (double-3) cryothermia applications for treatment of atrial flutter (AFL). Previous animal studies have indicated the need for a double 5-minute cryothermal application to create large and permanent lesions. Forty patients (56 +/- 13 years old) with typical AFL (cycle length 229 +/- 35 ms) were randomized to single-3 (n = 20) or double-3 (n = 20) cryothermia applications at each site along the cavotricuspid isthmus (CTI). Cryoablation was performed with the CryoCor cryoablation system. A successful procedure was defined as noninducibility of AFL with the concomitant presence of bidirectional CTI conduction block under isoproterenol infusion. All but 1 patient (95%) of the single-3 group and all patients (100%) of the double-3 group were successfully ablated. The number of sites needed to create isthmus conduction block was 9 +/- 4 (single-3) and 8 +/- 2 (double-3) (NS). Fluoroscopy time did not differ between the two groups (single-3: 31 +/- 14; double-3: 36 +/- 17 min, NS). The procedure time of the single-3 group was significantly shorter compared to the procedure time of the double-3 group (mean procedure duration 132 +/- 64 vs 159 +/- 50 min, P < .04). After a mean follow-up of 11.7 +/- 4.7 months, two recurrences of AFL occurred in the double-3 group. Single cryothermia applications of 3 minutes produce permanent CTI conduction block in patients with typical AFL and significantly reduce procedure duration.

Catheter-based cryoablation produces permanent bidirectional cavotricuspid isthmus conduction block in dogs.

Catheter-based cryoablation has been shown to produce punctate and effective cardiac lesions to treat focal targets. However, sequential applications are required to produce a continuous linear lesion needed to cure macroreentrant arrhythmias with large critical isthmuses. The purpose of this study was to compare and contrast linear cardiac lesions produced with sequential applications using a novel cryoablation system to those produced using radiofrequency (RF) energy. Seven mongrel dogs were prepared for femoral venous insertion of the ablation catheter (either a 10-French, 6-mm tipped, bipolar cryoablation catheter (N = 5, cryo group) or a 7-French, 4-mm tipped, bipolar RF ablation catheter (N = 2, RF group)). Ablation of the cavotricuspid isthmus was performed by delivering applications at sequential locations across the isthmus. The cryo group received 6 to 10 (mean 8 +/- 1.4), 5-minute applications at 3 to 5 separate sites with a mean nadir temperature of -74.5 +/- 1.6 degrees C. Each dog in the RF group received 9, 90-second applications with a mean temperature and power of 62 +/- 0 degrees C and 32 +/- 3.6 W. No acute or chronic complications were associated with either form of ablation. Immediately and six weeks after the index procedure, electroanatomical mapping showed the presence of bidirectional isthmus conduction block in all dogs. Gross and histopathologic examination revealed the presence of linear lesions, which were continuous and transmural. Similar to RF ablation, catheter-based cryoablation can produce linear, transmural lesions in the cavotricuspid isthmus resulting in permanent bidirectional isthmus conduction block.