The feasibility of using thermal strain imaging to regulate energy delivery during intracardiac radio-frequency ablation.

University of California, Davis, Department of Biomedical Engineering, Davis, CA, USA.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control (Impact Factor: 1.8). 07/2011; 58(7):1406-17. DOI: 10.1109/TUFFC.2011.1960
Source: PubMed

ABSTRACT A method is introduced to monitor cardiac ablative therapy by examining slope changes in the thermal strain curve caused by speed of sound variations with temperature. The sound speed of water-bearing tissue such as cardiac muscle increases with temperature. However, at temperatures above about 50°C, there is no further increase in the sound speed and the temperature coefficient may become slightly negative. For ablation therapy, an irreversible injury to tissue and a complete heart block occurs in the range of 48 to 50°C for a short period in accordance with the well-known Arrhenius equation. Using these two properties, we propose a potential tool to detect the moment when tissue damage occurs by using the reduced slope in the thermal strain curve as a function of heating time. We have illustrated the feasibility of this method initially using porcine myocardium in vitro. The method was further demonstrated in vivo, using a specially equipped ablation tip and an 11-MHz microlinear intracardiac echocardiography (ICE) array mounted on the tip of a catheter. The thermal strain curves showed a plateau, strongly suggesting that the temperature reached at least 50°C.

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