Impact of corticosteroids on late growth of radiofrequency lesions in infant pigs: histopathological and electroanatomical findings.
OBJECTIVE
Corticosteroids attenuate late growth of radiofrequency (RF) lesions in the thigh muscle of infant rats. We sought to assess the impact of these drugs on the late growth of RF lesions in immature swine myocardium and to determine the electroanatomical mapping (EAM) characteristics of these lesions.


RESULTS
Radiofrequency (60°C; 60 s) lesions were created in the right atrium (n = 2) and ventricle (n = 2) of 14 piglets (age 65 days; weight 5 kg) and 3 adults. Piglets were divided into: controls (n = 7) and treated (n = 7), receiving hydrocortisone (10 mg/kg iv after RF) and prednisone (1 mg/kg/day) for 29 days. After 8 months, animals were sacrificed for histological analysis. In four piglets, endocardial and epicardial voltage EAM were performed. In infant groups, the dimensions of atrial (11 ± 5 vs. 13 ± 7 mm) and ventricular (12 ± 3 vs. 11 ± 3 mm) lesions were similar. In adults, atrial (6 ± 1 mm) and ventricular (6 ± 1 mm) lesions were smaller. In controls, ventricular lesions depicted dense fibrosis and multiple strands of fibrous tissue extending from the lesion into normal muscle. Treated piglets revealed scars exhibiting less dense fibrosis with predominance of fibroadipose tissue and less collagen proliferation. Large atrial and ventricular low-voltage areas corresponding to the macroscopic lesions were identified in all animals.


CONCLUSIONS
Radiofrequency lesions in infant pigs reveal late growth and invasion of normal muscle by intense collagen proliferation. Corticosteroids do not prevent late enlargement of the lesions but modulate the fibrotic proliferation. The expressive growth of the lesion may generate low-voltage areas detectable by EAM.
Discipline of Cardiology, Paulista School of Medicine, Federal University of São Paulo-São Paulo, Rua Napoleão de Barros 715, SP-04039-030, São Paulo, Brazil.
Elerson
E
Arfelli
Sérgio
S
de Araujo
Mieko
M
Okada
Thais
T
Nascimento
Luis Felipe N
LF
dos Santos
Marcello
M
Franco
Angelo A V
AA
de Paola
Guilherme
G
Fenelon
D000305:Adrenal Cortex Hormones / Q000494:pharmacology*; D000818:Animals; D017115:Catheter Ablation; D049109:Cell Proliferation / Q000187:drug effects; D002921:Cicatrix / Q000473:pathology; D003094:Collagen / Q000378:metabolism; D005355:Fibrosis / Q000473:pathology; D006325:Heart Atria / Q000254:growth & development* / Q000473:pathology* / Q000601:surgery; D006352:Heart Ventricles / Q000254:growth & development* / Q000473:pathology* / Q000601:surgery; D006854:Hydrocortisone / Q000494:pharmacology; D023421:Models, Animal; D011241:Prednisone / Q000494:pharmacology; D013552:Swine
D000305:Adrenal Cortex Hormones; D003094:Collagen; D011241:Prednisone; D006854:Hydrocortisone