Contact force measurement in catheter ablation
LINZ, AUSTRIA. Radiofrequency-powered catheter ablation with the intent of curing atrial fibrillation (AF) involves the creation of lesions on the inside of heart tissue, primarily as rings encircling the areas where the pulmonary veins enter the left atrium (pulmonary vein isolation). In order to ensure a lasting cure, it is essential that lesions are created in the right locations, that there are no gaps in the lesion rings, and that transmurality is achieved – that is, that the depth of the lesions is as close to the outer wall of the pericardium as possible without penetrating it (cardiac tamponade). Thus, a successful ablation requires great tactile skill, an innate feel for just how much power to apply to any particular point and, of course, the support of sophisticated imaging equipment. It is clear that the force (contact force) with which the catheter is pressed against a particular area of heart tissue is of crucial importance in determining the ultimate lesion quality.

Biosense Webster recently released a new variation of its 3.5-mm, 8-hole, open-irrigated tip ablation catheter (Thermocool SmartTouch) which measures the force exerted by the catheter when pressed against the heart wall. A group of Austrian cardiologists/electrophysiologists now reports the results of the first clinical evaluation of the new catheter.

Fifty patients with paroxysmal AF were assigned to receive a circumferential pulmonary vein isolation procedure using either a standard 3.5 mm irrigated catheter (Thermocool) or the new force-sensing catheter (Thermocool SmartTouch). The average age of the patients was 59 years, 56% were male, 44% had hypertension, but none were reported as having cardiovascular disease. The average left atrial diameter was 38 mm. The ablation procedure was carried out using anatomically-guided mapping with the Carto3 system, which has a built-in feature showing catheter position and contact force on a continuous basis.

The total average procedure time for the conventional catheter group was 185 minutes as compared to 154 minutes for the contact force catheter group – a saving of 31 minutes. Similarly, the ablation time (minutes of actual radiofrequency application) was reduced by 11 minutes from 50 to 39 minutes. Total energy delivered during the procedure was reduced from 71,000 watt-seconds to 59,000 watt-seconds. Acute pulmonary vein connections following "first pass" ablation declined from 36% in the conventional catheter group to 12% in the contact force group. Complications were rare with one atrioventricular fistula, one pseudoaneurysm, and minimal pericardial effusion documented in the conventional catheter group, and one atrioventricular fistula and one case of pericardial tamponade documented in the contact force catheter group.

The Austrian researchers conclude that the use of contact force sensing technology is able to significantly reduce ablation and overall procedure time in pulmonary vein isolation procedures. However, they caution that the use of the new technology may actually increase perforation rate. Thus, whilst "40 g of force applied to a rigid thick tissue may be perfectly safe, the same force applied to thin pliable tissues will result in pouching and further tissue thinning which, coupled with radiofrequency application, may result in perforation".
Martinek, M, et al. Clinical impact of an open-irrigated radiofrequency catheter with direct force measurement on atrial fibrillation ablation. PACE, Vol. 35, November 2012, pp. 1312-18

Editor's comment: The use of a contact force-sensing catheter would, at first glance, seem to be a substantial improvement. However, it may be of value primarily for relatively inexperienced operators who have not developed the superior tactile skills characterizing the "top-gun" electrophysiologists performing ablations.