Thermotolerance does not reduce the size or remodeling of radiofrequency lesions in the rat myocardium.
OBJECTIVE
Late lesion extension may be involved in the genesis of delayed radiofrequency (RF) effects. Because RF lesion is thermally mediated, we hypothesized that induction of heat shock response (thermotolerance) would modulate lesion healing. We evaluated the effects of thermotolerance on the dimensions and remodeling of RF lesions in a rat model of heart failure.


METHODS
Wistar rats (weight 300 g) subjected to heat stress (n = 22, internal temperature of 42 °C for 10 min) were compared to controls (n = 22, internal temperature of 37 °C for 10 min). After 48 h (peak of HSP70 myocardial concentration), a modified unipolar RF lesion (customized catheter, tip 4.5 mm in diameter; 12 W; 10 s) was created on the left ventricular free wall. Animals were sacrificed 2 h (n = 10 per group) and 4 weeks (n = 12 per group) after ablation for lesion analysis. An echocardiogram was obtained at 4 weeks.


RESULTS
There was no difference between groups regarding the size of acute (controls 27 ± 2 vs. treated 27 ± 3 mm(2)) and chronic lesions (controls 17 ± 1 vs. treated 19 ± 1 mm(2)). Histology of lesions did not differ between groups. The echocardiogram revealed dilation of the cavities and moderate systolic dysfunction without difference between groups. Acute lesion dimensions were similar between control and treated animals over time (ablation undertaken 3, 12, 24, 48, and 72 h after hyperthermia) and also using a conventional ablation catheter (50 °C; 15 W; 10 s).


CONCLUSIONS
Thermotolerance does not reduce the size or remodeling of RF lesions in the rat myocardium.
Discipline of Cardiology, Paulista School of Medicine, Federal University of São Paulo, Pedro de Toledo 781, 10th Floor (Cardiology), São Paulo, SP 04039-032, Brazil.
Luís Felipe
LF
Dos Santos
Ednei Luíz
EL
Antonio
Andrey Jorge
AJ
Serra
Gabriela
G
Venturini
Jairo
J
Montemor
Mieko
M
Okada
Sergio
S
Araújo
Paulo
P
Tucci
Angelo
A
de Paola
Guilherme
G
Fenelon
D000818:Animals; D015153:Blotting, Western; D001831:Body Temperature; D017115:Catheter Ablation / Q000379:methods*; D016009:Chi-Square Distribution; D004195:Disease Models, Animal; D004452:Echocardiography; D006333:Heart Failure / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D009206:Myocardium; D051381:Rats; D017208:Rats, Wistar; D020257:Ventricular Remodeling / Q000502:physiology; D014945:Wound Healing