Histologic signatures of thermal injury: applications in transmyocardial laser revascularization and radiofrequency ablation.
OBJECTIVE
Cardiac treatments such as transmyocardial laser revascularization and radiofrequency ablation cause thermal injury. We sought to provide quantitative histologic methods of assessing such injury by using the inherent birefringence of cardiac muscle and collagen; specifically, to exploit the connection between thermal injury and the loss of birefringence.


METHODS
We quantified tissue birefringence changes in vitro for temperatures up to 130 degrees C. This information was used to assess thermal injury associated with myocardial channels made in vitro. We then measured in vivo cardiac injury 30 minutes and 3 days after radiofrequency exposure.


RESULTS
Birefringence decreased above 60 degrees C for muscle and above 70 degrees C for collagen. Temperatures above 80 degrees C were associated with collagen fiber straightening and above 95 degrees C with little muscle birefringence. Injury adjacent to laser channels was greatest parallel to cell orientation. In vivo, muscle with reduced birefringence was surrounded by cells exhibiting focal birefringence increases (contraction bands). Early injury assessment marked by birefringence changes corresponded to lesion size at 3 days.


CONCLUSIONS
Polarized light revealed histologic temperature signatures corresponding to irreversible muscle injury and collagen denaturation.
Whittaker
P
P
Heart Institute, Good Samaritan Hospital, & Department of Medicine, University of Southern California, Los Angeles, California 90017, USA. pwhittaker@dnamail.com
Zheng
S
S
Patterson
M J
MJ
Kloner
R A
RA
Daly
K E
KE
Hartman
R A
RA
D000818:Animals; D001831:Body Temperature; D017115:Catheter Ablation; D003094:Collagen / Q000032:analysis; D004285:Dogs; D053685:Laser Therapy / Q000009:adverse effects; D008854:Microscopy, Electron; D009206:Myocardium / Q000473:pathology*
D003094:Collagen