Feasability of transcoronary guidewire RF ablation

K. Heinroth (Halle (Saale))¹, D. Hoyer (Halle (Saale))², D. Mahnkopf (Rottmersleben)³, D. G. Sedding (Halle (Saale))^2
1Martha-Maria Krankenhaus Halle-Dölau GmbH Klinik für Innere Medizin I Halle (Saale), Deutschland; ²Universitätsklinikum Halle (Saale) Klinik und Poliklinik für Innere Medizin III Halle (Saale), Deutschland; ³IMTR Rottmersleben, Deutschland

Background
Transcoronary ablation of septal hypertrophy (TASH) is the recommended treatment option in patients with hypertrophic obstructive cardiomyopathy refractory to conventional drug treatment. More recently application of radiofrequency (RF) either via conventional RF-catheters or by transapical insertion of a RF-needle was used for reduction of LVOT-obstruction. We describe the application of RF-energy via coronary guidewires in an animal model for selective occlusion of coronary side branches mimicking the principle of TASH by occluding septal branches.

Methods
Transcoronary guidewire ablation of coronary vessels was investigated in 8 adult pigs under general anaesthesia in an animal cathlab after successful bench testing of the ablation settings. The study was approved by the local animal based research authorities. 
A standard floppy-tip guidewire insulated by a monorail balloon or a special guidewire with electrical insulation by PTFE coating except for the distal end of the wire were positioned in different coronary side branches. A skin patch electrode at the dorsal chest of the animal served as the indifferent electrode. 
After assessing transcoronary pacing parameters for validation of the electrical integrity of the system RF-energy was delivered via the guidewire-tip. Occlusion or patency of the specific coronary side branch was documented by coronary angiography after RF-delivery.
 
Results
Transcoronary pacing thresholds obtained against the RV electrode were (2.1±1.4 V) with a mean pacing impedance of 417 ± 65 Ohm. The magnitude of the local electrogram before the ablation was 5.9±4.0 mV.
In 15 vessels same measurements could be completed after the ablation procedure. 
As expected the pacing thresholds after the ablation procedure were higher (4.1±2.3 V) with a mean pacing impedance of 389 ± 41 Ohm and an R-wave amplitude of 4.9±2.2 mV.                                                             
After the transcoronary RF-ablation the intended occlusion of the coronary vessel (TIMI 0 or TIMI I-flow) could be verified by angiography in 82 % of the septal branches attempted and 79 % of the epicardial branches. The mean ablation duration was 10.3 s at 20 Watt power with an initial impedance of 176 ± 31 Ohm. An unintended occlusion of the donor vessel did not happen in any case.

Conclusions
RF-ablation via coronary guidewires is a feasible method for inducing an acute occlusion of coronary vessels.
This technique may change the interventional therapy of HOCM by obliterating septal branches without the risks associated with ethanol injection. 
Our in vitro and in vivo animal data have to be validated in human even there are some case reports applying this method in the coronary venous system for VT-ablation.
If the safety of this approach could be proved and with the availability of insulated coronary guidewires (ideally tip coated by platinum/gold), tip temperature sensors and saline cooling via microcatheters this technique could potentially replace ethanol injection in TASH procedures.