Myocardial lesion formation using high-intensity focused ultrasound

The potential therapeutic uses of ultrasound energy in cardiac disease have not been extensively studied. We have developed a means to deliver high-intensity focused ultrasound (HIFU) to myocardial tissue. Unlike other therapy modalities such as radiofrequency catheter ablation, this system has the advantages of not requiring direct tissue contact and the ability to focus intense energy within a small volume.

Sections of left and right ventricles from freshly excised canine hearts were treated in vitro with HIFU pulses. Lesions were created using 1-second HIFU pulses with ultrasonic powers ranging from 19.8 to 45.8 W.

There was a dose-response relationship between the applied HIFU energy and lesion size (r = 0.70, P < .001). Myocardial lesion formation with HIFU was also performed in vivo in a canine open-chest beating heart model. With 200-millisecond HIFU pulses gated to the electrocardiogram, focal myocardial lesions were created ranging in length from 2 to 6 mm depending on the dose used. Furthermore, both in vitro and in vivo, focal lesions were successfully formed in the midmyocardial wall that spared both the endocardial and epicardial surfaces.

HIFU is a novel means to create focal myocardial lesions without direct tissue contact. HIFU energy delivery can be gated to the electrocardiogram in an in vivo model, and lesions can be formed intramyocardially. Further application of this technology may prove to be useful for the ablation of myocardial lesions such as arrhythmogenic foci and the hypertrophic ventricular septum in hypertrophic cardiomyopathy. The potential therapeutic uses of ultrasound energy in cardiac diseases have not been well studied. We tested a novel system to deliver high-intensity focused ultrasound energy in vitro and in vivo to canine myocardial samples without direct contact with the target tissue. Focal myocardial lesions were formed in a dose-dependent manner, and myocardial lesions were created. This technology may prove useful for ablation of focal intramyocardial lesions such as arrhythmogenic foci and the hypertrophic left ventricular septum in hypertrophic cardiomyopathy.