Sarah E. Ahlberg

Microembolism and catheter ablation I: a comparison of irrigated radiofrequency and multielectrode-phased radiofrequency catheter ablation of pulmonary vein ostia.

Background—Cerebral diffusion-weighted MRI lesions have been observed after catheter ablation of atrial fibrillation. We hypothesized that conditions predisposing to microembolization could be identified using a porcine model of pulmonary vein ablation and an extracorporeal circulation loop. Methods and Results—Ablations of the pulmonary veins were performed in 18 swine with echo monitoring. The femoral artery and vein were cannulated and an extracorporeal circulation loop with 2 ultrasonic bubble detectors and a 73-&mgr;m filter were placed in series. Microemboli and microbubbles were compared between ablation with an irrigated radiofrequency system (Biosense-Webster) and a phased radiofrequency multielectrode system (pulmonary vein ablation catheter [PVAC], Medtronic, Inc, Carlsbad, CA) in unipolar and 3 blended unipolar/bipolar modes. Animal pathology was examined. The size and number of microbubbles observed during ablation ranged from 30 to 180 &mgr;m and 0 to 3253 bubbles per ablation. Microbubble volumes with PVAC (29.1 nL) were greater than with irrigated radiofrequency (0.4 nL; P=0.045), and greatest with type II or III microbubbles on transesophageal echocardiography. Ablation with the PVAC showed fewest microbubbles in the unipolar mode (P=0.012 versus bipolar). The most occurred during bipolar energy delivery with overlap of proximal and distal electrodes (median microbubble volume, 1744 nL; interquartile range, 737–4082 nL; maximum, 19 516 nL). No cerebral MRI lesions were seen, but 2 animals had renal embolization. Conclusions—Left atrial ablation with irrigated radiofrequency and PVAC catheters in swine is associated with microbubble and microembolus production. Avoiding overlap of electrodes 1 and 10 on PVAC should reduce the microembolic burden associated with this procedure.Background— Cerebral diffusion-weighted MRI lesions have been observed after catheter ablation of atrial fibrillation. We hypothesized that conditions predisposing to microembolization could be identified using a porcine model of pulmonary vein ablation and an extracorporeal circulation loop. Methods and Results— Ablations of the pulmonary veins were performed in 18 swine with echo monitoring. The femoral artery and vein were cannulated and an extracorporeal circulation loop with 2 ultrasonic bubble detectors and a 73-μm filter were placed in series. Microemboli and microbubbles were compared between ablation with an irrigated radiofrequency system (Biosense-Webster) and a phased radiofrequency multielectrode system (pulmonary vein ablation catheter [PVAC], Medtronic, Inc, Carlsbad, CA) in unipolar and 3 blended unipolar/bipolar modes. Animal pathology was examined. The size and number of microbubbles observed during ablation ranged from 30 to 180 μm and 0 to 3253 bubbles per ablation. Microbubble volumes with PVAC (29.1 nL) were greater than with irrigated radiofrequency (0.4 nL; P =0.045), and greatest with type II or III microbubbles on transesophageal echocardiography. Ablation with the PVAC showed fewest microbubbles in the unipolar mode ( P =0.012 versus bipolar). The most occurred during bipolar energy delivery with overlap of proximal and distal electrodes (median microbubble volume, 1744 nL; interquartile range, 737–4082 nL; maximum, 19 516 nL). No cerebral MRI lesions were seen, but 2 animals had renal embolization. Conclusions— Left atrial ablation with irrigated radiofrequency and PVAC catheters in swine is associated with microbubble and microembolus production. Avoiding overlap of electrodes 1 and 10 on PVAC should reduce the microembolic burden associated with this procedure.

Microembolism and Catheter Ablation IClinical Perspective

Background—Cerebral diffusion-weighted MRI lesions have been observed after catheter ablation of atrial fibrillation. We hypothesized that conditions predisposing to microembolization could be identified using a porcine model of pulmonary vein ablation and an extracorporeal circulation loop. Methods and Results—Ablations of the pulmonary veins were performed in 18 swine with echo monitoring. The femoral artery and vein were cannulated and an extracorporeal circulation loop with 2 ultrasonic bubble detectors and a 73-&mgr;m filter were placed in series. Microemboli and microbubbles were compared between ablation with an irrigated radiofrequency system (Biosense-Webster) and a phased radiofrequency multielectrode system (pulmonary vein ablation catheter [PVAC], Medtronic, Inc, Carlsbad, CA) in unipolar and 3 blended unipolar/bipolar modes. Animal pathology was examined. The size and number of microbubbles observed during ablation ranged from 30 to 180 &mgr;m and 0 to 3253 bubbles per ablation. Microbubble volumes with PVAC (29.1 nL) were greater than with irrigated radiofrequency (0.4 nL; P=0.045), and greatest with type II or III microbubbles on transesophageal echocardiography. Ablation with the PVAC showed fewest microbubbles in the unipolar mode (P=0.012 versus bipolar). The most occurred during bipolar energy delivery with overlap of proximal and distal electrodes (median microbubble volume, 1744 nL; interquartile range, 737–4082 nL; maximum, 19 516 nL). No cerebral MRI lesions were seen, but 2 animals had renal embolization. Conclusions—Left atrial ablation with irrigated radiofrequency and PVAC catheters in swine is associated with microbubble and microembolus production. Avoiding overlap of electrodes 1 and 10 on PVAC should reduce the microembolic burden associated with this procedure.Background— Cerebral diffusion-weighted MRI lesions have been observed after catheter ablation of atrial fibrillation. We hypothesized that conditions predisposing to microembolization could be identified using a porcine model of pulmonary vein ablation and an extracorporeal circulation loop. Methods and Results— Ablations of the pulmonary veins were performed in 18 swine with echo monitoring. The femoral artery and vein were cannulated and an extracorporeal circulation loop with 2 ultrasonic bubble detectors and a 73-μm filter were placed in series. Microemboli and microbubbles were compared between ablation with an irrigated radiofrequency system (Biosense-Webster) and a phased radiofrequency multielectrode system (pulmonary vein ablation catheter [PVAC], Medtronic, Inc, Carlsbad, CA) in unipolar and 3 blended unipolar/bipolar modes. Animal pathology was examined. The size and number of microbubbles observed during ablation ranged from 30 to 180 μm and 0 to 3253 bubbles per ablation. Microbubble volumes with PVAC (29.1 nL) were greater than with irrigated radiofrequency (0.4 nL; P =0.045), and greatest with type II or III microbubbles on transesophageal echocardiography. Ablation with the PVAC showed fewest microbubbles in the unipolar mode ( P =0.012 versus bipolar). The most occurred during bipolar energy delivery with overlap of proximal and distal electrodes (median microbubble volume, 1744 nL; interquartile range, 737–4082 nL; maximum, 19 516 nL). No cerebral MRI lesions were seen, but 2 animals had renal embolization. Conclusions— Left atrial ablation with irrigated radiofrequency and PVAC catheters in swine is associated with microbubble and microembolus production. Avoiding overlap of electrodes 1 and 10 on PVAC should reduce the microembolic burden associated with this procedure.

Estimation of global ventricular activation sequences by noninvasive three-dimensional electrical imaging: Validation studies in a swine model during pacing

Background: A novel noninvasive imaging technique, the heart‐model‐based three‐dimensional cardiac electrical imaging (3DCEI) approach was previously developed and validated to estimate the initiation site (IS) of cardiac activity and the activation sequence (AS) from body surface potential maps (BSPMs) in a rabbit model. The aim of the present study was to validate the 3DCEI in an intact large mammalian model (swine) during acute ventricular pacing.

Animal Models for Cardiac Valve Research

In the current regulatory climate, the Food and Drug Administration requires that all invasive cardiac devices are subjected to in vivo testing prior to human clinical trials and/or medical use. The most effective method for assessing the in vivo performance, durability, and biocompatibility of a novel heart valve therapy is through testing within the appropriate animal model. For replacement heart valves, preclinical testing is performed under strict regulatory guidelines to critically assess the performance of the device and the response of the host, by accurately replicating the intended human implantation procedure. This ensures the collection of relevant data and minimizes the potential for distress or discomfort to the test subject. The fundamental goals of a preclinical study are to report any detectable pathological consequences of the procedure, to report any macro- or microscopically detectable structural alterations in the device itself, and to histologically assess any thromboembolic material, inflammatory reactions, or degenerative processes. The success of a preclinical trial relies on careful protocol design, choosing the appropriate animal model, and adhering to the regulatory guidelines for Good Laboratory Practices. Importantly, the continued use of animal models in cardiac research has also benefited the field of veterinary science and, until in vitro and in silico methods provide suitable alternatives, will continue to be the most accurate assessment for the next generations of valve therapies.

Novel visualization of intracardiac pacing lead extractions: Methodologies performed within isolated canine hearts

Several methodologies are typically employed to extract chronically-implanted pacing leads including: laser catheter systems, radio frequency catheters, mechanical cutting catheters, and/or direct traction. In the present study, Visible Heart® methodologies were employed to obtain novel internal and external views of such extractions. Utilizing standard cardioplegia procedures, canine hearts (n = 3) with chronically-implanted endocardial pacing leads were explanted to a unique isolated heart apparatus. Modified Krebs–Henseleit buffer allowed for clear endocardial imaging with endoscopic video cameras inserted into the cardiac chambers. Leads were extracted using: (1) laser system with sheath; (2) dissection sheath with incorporated bipolar tungsten electrode; (3) non-powered mechanical sheath; or (4) direct traction. Resultant images provide a novel perspective regarding lead extraction methodologies and the imposed force on an encapsulated lead and on the great vessels and/or heart itself; this understanding may improve the outcome and safety of future lead extractions.

Microembolism and Catheter Ablation IClinical Perspective: A Comparison of Irrigated Radiofrequency and Multielectrode-phased Radiofrequency Catheter Ablation of Pulmonary Vein Ostia

Background—Cerebral diffusion-weighted MRI lesions have been observed after catheter ablation of atrial fibrillation. We hypothesized that conditions predisposing to microembolization could be identified using a porcine model of pulmonary vein ablation and an extracorporeal circulation loop. Methods and Results—Ablations of the pulmonary veins were performed in 18 swine with echo monitoring. The femoral artery and vein were cannulated and an extracorporeal circulation loop with 2 ultrasonic bubble detectors and a 73-&mgr;m filter were placed in series. Microemboli and microbubbles were compared between ablation with an irrigated radiofrequency system (Biosense-Webster) and a phased radiofrequency multielectrode system (pulmonary vein ablation catheter [PVAC], Medtronic, Inc, Carlsbad, CA) in unipolar and 3 blended unipolar/bipolar modes. Animal pathology was examined. The size and number of microbubbles observed during ablation ranged from 30 to 180 &mgr;m and 0 to 3253 bubbles per ablation. Microbubble volumes with PVAC (29.1 nL) were greater than with irrigated radiofrequency (0.4 nL; P=0.045), and greatest with type II or III microbubbles on transesophageal echocardiography. Ablation with the PVAC showed fewest microbubbles in the unipolar mode (P=0.012 versus bipolar). The most occurred during bipolar energy delivery with overlap of proximal and distal electrodes (median microbubble volume, 1744 nL; interquartile range, 737–4082 nL; maximum, 19 516 nL). No cerebral MRI lesions were seen, but 2 animals had renal embolization. Conclusions—Left atrial ablation with irrigated radiofrequency and PVAC catheters in swine is associated with microbubble and microembolus production. Avoiding overlap of electrodes 1 and 10 on PVAC should reduce the microembolic burden associated with this procedure.Background— Cerebral diffusion-weighted MRI lesions have been observed after catheter ablation of atrial fibrillation. We hypothesized that conditions predisposing to microembolization could be identified using a porcine model of pulmonary vein ablation and an extracorporeal circulation loop. Methods and Results— Ablations of the pulmonary veins were performed in 18 swine with echo monitoring. The femoral artery and vein were cannulated and an extracorporeal circulation loop with 2 ultrasonic bubble detectors and a 73-μm filter were placed in series. Microemboli and microbubbles were compared between ablation with an irrigated radiofrequency system (Biosense-Webster) and a phased radiofrequency multielectrode system (pulmonary vein ablation catheter [PVAC], Medtronic, Inc, Carlsbad, CA) in unipolar and 3 blended unipolar/bipolar modes. Animal pathology was examined. The size and number of microbubbles observed during ablation ranged from 30 to 180 μm and 0 to 3253 bubbles per ablation. Microbubble volumes with PVAC (29.1 nL) were greater than with irrigated radiofrequency (0.4 nL; P =0.045), and greatest with type II or III microbubbles on transesophageal echocardiography. Ablation with the PVAC showed fewest microbubbles in the unipolar mode ( P =0.012 versus bipolar). The most occurred during bipolar energy delivery with overlap of proximal and distal electrodes (median microbubble volume, 1744 nL; interquartile range, 737–4082 nL; maximum, 19 516 nL). No cerebral MRI lesions were seen, but 2 animals had renal embolization. Conclusions— Left atrial ablation with irrigated radiofrequency and PVAC catheters in swine is associated with microbubble and microembolus production. Avoiding overlap of electrodes 1 and 10 on PVAC should reduce the microembolic burden associated with this procedure.

Exit vs. entrance block testing for cardiac lesion assessment

Cardiac lesions are created to act as barriers which prohibit the transmission of cardiac myocyte contractile activity from one side of the lesion to the other. Testing for conduction block is the main way to acutely confirm the effectiveness of this therapy. There are two general methods used to test for conduction block. These methods are called: 1) “exit block testing” and 2) “entrance block testing.” In this study, two different devices were used on n = 3D5 swine to determine if the method of lesion assessment (exit vs. entrance block testing) affected the ability to correctly identify if acute conduction block was achieved. No significant difference was found between conclusions drawn from either method of lesion assessment. However, the most robust lesion assessment will occur when both methods are employed so that the physician has the most information available for analysis.

Noninvasive estimation of three-dimensional cardiac electrical activities from body surface potential maps

A noninvasive three-dimensional (3D) cardiac electrical imaging (3DCEI) approach, which can estimate the location of the initiation site (IS) of activation and the resultant 3D activation sequence (AS) from body surface potential maps (BSPMs), was validated in an intact large mammalian model (swine) during acute ventricular pacing. Body surface potential mapping and intracavitary noncontact mapping (NCM) were performed simultaneously during pacing from both right ventricular (RV) sites (intramural) and left ventricular (LV) sites (endocardial). Subsequent 3DCEI analyses were performed on the measured BSPMs. In total, 5 RV and 5 LV sites from control and heart failure animals were paced. The averaged localization error of the RV and LV sites were 7.0±1.1 mm and 6.6±1.9 mm, respectively. The endocardial ASs as a subset of the estimated 3D ASs by 3DCEI were consistent with those reconstructed from the NCM system. The present experimental results demonstrate that the noninvasive 3DCEI approach can localize the initiation site and estimate cardiac activation sequence with good accuracy in an in vivo setting, under control, paced and/or diseased conditions.