DJR Guy*, HM Chiu⁺, AS Mohan⁺, SP Thomas, DL Ross.

Department of Cardiology, Westmead Hospital and ⁺Telecoms Group, Faculty of Engineering, University of Technology, Sydney.

Antenna design is a critical factor for efficient coupling of microwave energy to the myocardium for ablation. Using finite difference time domain antenna modelling we designed a novel array antenna and tested its performance in a tissue phantom gel.  The radiated field appeared suitable for long linear atrial ablation and deep ventricular ablation..  The array was constructed from 2.2mm diameter high energy cable. The effect of power and duration of ablation on lesion size was investigated to determine if this array would be suitable for creating transmural lesions in atrial or ventricular myocardium. Under anaesthesia hearts and blood were removed from 8 sheep. The hearts were mounted in a perspex chamber and superfused with the heparinised oxygenated blood with a flow rate of 3l/min, the temperature maintained at 37 degrees Celsius. 4 lesions were created on the left ventricular endocardial surface in each of 8 hearts. The lesions were stained with nitroblue tetrazolium, sectioned at the mid point of the lesion, digitally photographed and measured with Scion image software.

There was no surface charring or crater formation.  Lesions were deeper (p=0.012) and wider (p<0.0001) with higher power settings.  Longer duration of ablation produced deeper (p=0.008) and wider (p=0.027) lesions.  The width/depth ratio increased with power (p=0.016) but not duration (p=0.37).

In relatively short time periods this novel array antenna produced lesions of sufficient depth for transmural atrial, and in some cases transmural ventricular ablation. Varying the power used and the duration of the ablation has a significant effect on lesion size.

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