Evaluation of epicardial microwave ablation lesions: histology versus electrophysiology.
BACKGROUND
Pulmonary vein isolation is a hallmark in current surgical ablation for atrial fibrillation. However, validation of isolation remains cumbersome. We evaluated electrophysiologic and not histologic means to test isolation.


METHODS
In 16 mongrel dogs, robot-assisted epicardial beating-heart microwave ablation (FLEX 10) was performed around the pulmonary veins. Electrophysiologic isolation was tested by pacing at 4 times threshold values inside and outside the pulmonary veins (exit and entrance block). The histology of lesions was studied for transmurality and continuity of the lesion lines. In 5 dogs, lesions were studied at various time intervals.


RESULTS
Histologic evaluation of the lesions showed incomplete (48% +/- 20%) circumferential myocardial damage in all dogs with acute lesions. Electrophysiologic evaluation showed completion of the box (entrance and exit block) in 8 dogs and in another 5 dogs after repeated ablation (p < 0.01 compared with histologic evaluation). Electrophysiologic evaluation of the dogs with chronic lesions showed completed lesions in 4 of 5 dogs directly after ablation. At follow-up (1 to 3 weeks), the isolations remained electrophysiologically complete. Histologic evaluation of the lesions 1 to 3 weeks after ablation showed complete (100%) circumferential lesions in all 4 dogs (p < 0.001 compared with the histology of dogs with acute lesions).


CONCLUSIONS
Directly after treatment, ablation lesions are best evaluated electrophysiologically, because complete (transmural and circumferential) lesions are not shown by histologic evaluation in the acute stage. After 1 to 3 weeks, the histology is in accordance with the electrophysiology. To obtain a complete isolation, online electrophysiologic evaluation during pulmonary vein microwave ablation is necessary to optimize the results.
Department of Cardiothoracic Surgery and Physiology, Cardiovascular Research Institute Maastricht, Maastricht, The Netherlands. t.vanbrakel@ctc.unimaas.nl
Thomas J
TJ
van Brakel
Gil
G
Bolotin
Kenneth J
KJ
Salleng
L Wiley
LW
Nifong
Maurits A
MA
Allessie
W Randolph
WR
Chitwood
Jos G
JG
Maessen
D000818:Animals; D002304:Cardiac Pacing, Artificial; D017115:Catheter Ablation / Q000009:adverse effects / Q000379:methods; D004285:Dogs; D006321:Heart / Q000503:physiopathology* / Q000528:radiation effects; D006325:Heart Atria; D008872:Microwaves / Q000009:adverse effects / Q000627:therapeutic use*; D009206:Myocardium / Q000473:pathology*; D032383:Myocytes, Cardiac / Q000473:pathology / Q000528:radiation effects; D009336:Necrosis; D011184:Postoperative Period; D011667:Pulmonary Veins / Q000601:surgery*; D011832:Radiation Injuries / Q000209:etiology / Q000473:pathology; D012371:Robotics