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An abstract of the article "Voltage-based electroanatomic mapping system for MR-guided cardiac electrophysiology: preliminary swine validations," by Zion Tse and colleagues is presented.

One factor which may be important for determining proper lesion creation in an atrial ablation procedure is catheter-endocardial contact. Little information is available that relates geometric contact, depth and angle, to ablation lesion formation. We present an electrothermal computer model of ablation that calculates lesion volume and temperature development over time. The Pennes bioheat equation was coupled to a quasistatic electrical problem. This method simulates importantly, not just catheter penetration depth, but also several different incident catheter angles as may occur in practise. Results show that for deeply penetrating tips, greater catheter angles reduce the rate of temperature buildup, allowing for larger lesions to form before temperatures become dangerous. It was also found that greater penetration may not lead to greater transmurality in lesion formation. We conclude that catheter contact angle plays a significant role in lesion formation, and the time course must be considered. This is clinically relevant because it makes proper identification and prediction of geometric contact variables a necessity in order to improve ablation efficacy and safety.

Convention holds that the magnitude of an electrogram (EGM) recorded from an ablation catheter indicates proximity to the tissue and may be used to guide tip placement. The shift in capacitance (phase angle) as the electrode touches the tissue may be a better guide. We compared these two methods over a range of distances in close proximity to heart tissue. This study suggests that EGM is not a reliable predictor of proximity to tissue within a few millimeters of the surface. Thus, EGM alone should not be used to guide electrode placement for ablation, as a millimeter off the surface will shift a greater percentage of delivered energy to the blood pool rather than the target tissue. EGM should also not be used to gauge force of the catheter into tissue. Phase angle is a better predictor of both variables, but an optimal combination of predictors remains to be found.

Interactions between paced wavefronts and monomorphic ventricular tachycardia (VT) dictate antitachycardia pacing outcomes. Monomorphic VTs were initiated in isolated rabbit hearts (n=6) that were endocardially cryoablated to limit viable tissue to the visible epicardium and the ablated apex served as an anatomic anchor. Preparations were optically mapped during single and dual site pacing at 50% to 90% of VT cycle length with 8 pulses per trial. Of these trials, responses to the 48 single site pulses and to the 172 dual site pulses that captured tissue were analyzed. Overall, we found most pulses reset the VT, and a small number of pulses that abruptly terminated the VT. Of particular interest, we found 12 pulses that shifted the anatomically anchored VT to functionally reentrant wavefronts, and thereby induced polymorphic VT. Delayed termination was observed following 6 of these instances, and the underlying non-sustained polymorphic VT's presented temporal characteristics similar to those presented by delayed termination after antitachycardia pacing in ICD patients.