Brian D. Pederson

Validation of a New Noncontact Catheter System for Electroanatomic Mapping of Left Ventricular Endocardium

BACKGROUND Improvements in cardiac mapping are required to advance our understanding and treatment of arrhythmias. This study validated a new noncontact multielectrode array catheter and accompanying analysis system to provide electroanatomic mapping of the entire left ventricular (LV) endocardium during a single beat. METHODS AND RESULTS A 9F 64-electrode balloon array catheter with an inflated size of 1.8x4.6 cm was used to simultaneously record electrical potentials generated by the heart and locate a standard electrophysiology (EP) catheter within the same chamber. By use of the recorded location of the EP-catheter tip, LV geometry was determined. Array potentials served as inputs to a high-order boundary-element method to produce 3360 potential points on the endocardial surface translatable into electrograms or color-coded activation maps. Three methods of validation were used: (1) driven electrodes in an in vitro tank were located; (2) waveforms generated from the array catheter were compared with catheter contact waveforms in canine LV; and (3) sites of local LV endocardial activation were located and marked with radiofrequency lesions. Tank testing located a driven electrode to within 2.33+/-0.44 mm. Correlation of timing and morphology of computed versus contact electrograms was 0.966. Radiofrequency lesions marked 17 endocardial pacing sites to within 4.0+/-3.2 mm. CONCLUSIONS This new system provides anatomically accurate endocardial isopotential mapping during a single cardiac cycle. The locator component enabled placement of a separate EP catheter to any site within the mapped chamber.

Mapping of Atrial Activation With a Noncontact, Multielectrode Catheter in Dogs

BACKGROUND Endocardial mapping of sustained arrhythmias has traditionally been performed with a roving diagnostic catheter. Although this approach is adequate for many tachyarrhythmias, it has limitations. The purpose of this study was to evaluate a novel noncontact mapping system for assessing atrial tachyarrhythmias. METHODS AND RESULTS The mapping system consists of a 9F multielectrode-array balloon catheter that has 64 active electrodes and ring electrodes for emitting a locator signal. The locator signal was used to construct a 3-dimensional right atrial map; it was independently validated and was highly accurate. Virtual electrograms were calculated at 3360 endocardial sites in the right atrium. We evaluated right atrial activation by positioning the balloon catheter in the mid right atrium via a femoral venous approach. Experiments were performed on 12 normal mongrel dogs. The mean correlation coefficient between contact and virtual electrograms was 0.80+/-0.12 during sinus rhythm. Fifty episodes of atrial flutter induced in 11 animals were evaluated. In the majority of experiments, complete or almost complete reentrant circuits could be identified within the right atrium. Mean correlation coefficient between virtual and contact electrograms was 0.85+/-0.17 in atrial flutter. One hundred fifty-six episodes of pacing-induced atrial fibrillation were evaluated in 11 animals. Several distinct patterns of right atrial activation were seen, including single-activation wave fronts and multiple simultaneous-activation wave fronts. Mean correlation coefficient between virtual and contact electrograms during atrial fibrillation was 0.81+/-0.18. The accuracy of electrogram reconstruction was lower at sites >4.0 cm from the balloon center and at sites with a high spatial complexity of electrical activation. CONCLUSIONS This novel noncontact mapping system can evaluate conduction patterns during sinus rhythm, demonstrate reentry during atrial flutter, and describe right atrial activation during atrial fibrillation. The accuracy of electrogram reconstruction was good at sites <4.0 cm from the balloon center, and thus the system has the ability to perform high-resolution multisite mapping of atrial tachyarrhythmias in vivo.

Measurement of Ventricular Volume by Intracardiac Impedance: Theoretical and Empinrcal Approaches

The most widely used equation, V = pL2/R, is developed for the computation of ventricular volume from catheter based impedance measurements. The assumptions implicit in this derivation are examined and found to be generally invalid. An empirical discrete resistor model is described which includes the impedance of the myocardial tissue and the adjoining ventricular blood volume. Once the parameters of this model are determined for individual canine hearts, the model predicts stroke volume from measured impedances. Due to the difficulty involved in determining the parameters of the empirical model, a numerical model is developed which solves the equation V ¿a V U + F = 0 in a three-dimensional volume. This model is then used to determine the effect of parallel tissue resistance, catheter position, and contraction of the other ventricle on volumes computed by intracardiac impedance. Parallel tissue resistance is found to have the greatest impact on absolute volume measurements. However, stroke volume computations are relatively unaffected by any of the three factors.

The feasibility of utilizing the systolic pre-ejection interval as a determinant of pacing rate☆

Rate-modulated pacing modes adjust the stimulus rate by responding to sensed alterations in physiologic indexes of metabolic demand. This study was designed to determine whether right ventricular pre-ejection interval, measured in patients by a prototype pacemaker system capable of tracking intraventricular volume, changes predictably with exercise and, if so, whether it can be used in an algorithm to vary heart rate appropriately. This system utilizes intraventricular electrical impedance measurements of injected microampere currents to determine intracavitary volume changes. Five pacemaker-dependent patients underwent temporary insertion of a tripolar electrode connected to an external device that sensed cardiac signals, generated an impedance wave form and produced stimuli at rates dependent on pre-ejection interval. Pre-ejection interval did not change as a result of variations in pacing rate itself (347 +/- 41 ms at 70 beats/min versus 321 +/- 19 ms at 130 beats/min), but consistently decreased during graded exercise (by 23% from baseline). During rate-modulated pacing based on pre-ejection interval, heart rate significantly increased during exercise compared with ventricular demand pacing (by 46 +/- 6 versus 7 +/- 6 beats/min, respectively), and increased appropriately during burst exercise. Thus, the pre-ejection interval appears to be a specific, reliable physiologic determinant of pacing rate during exertion, which may be applicable in implantable rate-modulated pacemakers.