Zachary J Malchano

Partners HealthCare, Boston, Massachusetts, United States

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Publications (13)88.46 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Recent data suggests that the cardiac autonomic nervous system has an important role in the initiation and maintenance of atrial fibrillation (AF). This study investigated (1) the feasibility of identifying and targeting these autonomic ganglia using endocardial radiofrequency stimulation and ablation, respectively; (2) the efficacy of endocardial ablation to completely eliminate the vagal response elicited from epicardial stimulation; and (3) the effect of autonomic ablation on the acute inducibility of AF. The study included 18 patients referred for catheter ablation of suspected vagal-mediated AF. The endocardial left atrial surface was stimulated at high frequency (20 to 50 Hz) to elicit a vagal response. In selected patients (n = 5), pericardial access was obtained using a subxyphoid puncture to permit epicardial stimulation. Catheter ablation of the putative autonomic ganglionic sites was performed from the left atrial endocardium using irrigated radiofrequency energy. After ablation of all identifiable autonomic ganglia, high-frequency pacing was repeated to induce AF. In all patients, stimulation at certain endocardial sites elicited a vagal response. Endocardial ablation abrogated this vagal responsiveness. Furthermore, for sites accessible from the pericardium, the vagal response elicited using epicardial stimulation was also eliminated. Despite successful ablation of these ganglia, AF was still inducible in 17 of 18 patients. In conclusion, successful ablation of autonomic ganglia from an endocardial approach can be reliably achieved using an irrigated catheter. In addition, ablation of these structures in patients with vagal-mediated AF is insufficient to prevent its acute reinduction with high-frequency atrial stimulation.
    The American Journal of Cardiology 10/2008; 102(5):578-83. · 3.21 Impact Factor
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    ABSTRACT: X-ray fluoroscopy constitutes the fundamental imaging modality for catheter visualization during interventional electrophysiology procedures. The minimal tissue discriminative capability of fluoroscopy is mitigated in part by the use of electroanatomic mapping systems and enhanced by the integration of preacquired 3-dimensional imaging of the heart with computed tomographic or magnetic resonance (MR) imaging. A more ideal paradigm might be to use intraprocedural MR imaging to directly image and guide catheter mapping procedures. An MR imaging-based electroanatomic mapping system was designed to assess the feasibility of navigating catheters to the left ventricle in vivo using MR tracking of microcoils incorporated into the catheters, measuring intracardiac ventricular electrograms, and integrating this information with 3-dimensional MR angiography and myocardial delayed enhancement images to allow ventricular substrate mapping. In all animals (4 normal, and 10 chronically infarcted swine), after transseptal puncture under fluoroscopic guidance, catheters were successfully navigated to the left ventricle with MR tracking (13 to 15 frames per second) by both transseptal and retrograde aortic approaches. Electrogram artifacts related to the MR imaging gradient pulses were successfully removed with analog and digital signal processing. In all animals, it was possible to map the entire left ventricle and to project electrogram voltage amplitude maps to identify the scarred myocardium. It is possible to use MR tracking to navigate catheters to the left ventricle, to measure electrogram activity, and to render accurate 3-dimensional voltage maps in a porcine model of chronic myocardial infarction, completely in the MR imaging environment. Myocardial delayed enhancement guidance provided dense sampling of the proximity of the infarct and accurate localization of complex infarcts.
    Circulation 09/2008; 118(8):853-62. · 15.20 Impact Factor
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    ABSTRACT: Unlike the initial balloon ablation catheters that were designed to deliver ablation lesions within the pulmonary veins (PVs), the current balloon prototypes are fashioned to deliver lesions at the PV ostia. Using electroanatomical mapping, this study evaluates the actual location of ablation lesions generated by cryo-based, laser-based, or ultrasound-based balloon catheters. In a total of 14 patients with paroxysmal atrial fibrillation, PV isolation was performed using either a cryoballoon catheter (8 patients), laser catheter (4 patients) or ultrasound balloon catheter (2 patients). Patients underwent preprocedural computed tomographic/magnetic resonance imaging. An intracardiac ultrasound catheter was used to aid in positioning the balloon catheter at the PV ostium/antrum. In all patients, sinus rhythm bipolar voltage amplitude maps (using either CARTO with computed tomographic/magnetic resonance image integration or NavX mapping) were generated at baseline and after electrical PV isolation as confirmed by use of a circular mapping catheter. Electrical isolation was achieved in 100% of the PVs. Electroanatomical mapping revealed that after ablation with any of the 3 balloon catheters, the extent of isolation included the tubular portions of each PV to the level of the PV ostia. However, the PV antral portions were left largely unablated with all 3 balloon technologies. Using the current generation of balloon ablation catheters, electrical isolation occurs at the level of the PV ostia, but the antral regions are largely unablated.
    Heart Rhythm 04/2008; 5(3):353-60. · 5.05 Impact Factor
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    ABSTRACT: A robotic catheter navigation system has been developed that provides a significant degree of freedom of catheter movement. This study examines the feasibility of synchronizing this robotic navigation system with electroanatomic mapping and 3-dimensional computed tomography imaging to perform view-synchronized left atrial (LA) ablation. This study consisted of a porcine experimental validation phase (9 animals) and a clinical feasibility phase (9 atrial fibrillation patients). Preprocedural computed tomography images were reconstructed to provide 3-dimensional surface models of the LA pulmonary veins and aorta. Aortic electroanatomic mapping was performed manually, followed by registration with the corresponding computed tomography aorta image using custom software. The mapping catheter was remotely manipulated with the robotic navigation system within the registered computed tomography image of the LA pulmonary veins. The point-to-surface error between the LA electroanatomic mapping data and the computed tomography image was 2.1+/-0.7 and 1.6+/-0.1 mm in the preclinical and clinical studies, respectively. The catheter was remotely navigated into all pulmonary veins, the LA appendage, and circumferentially along the mitral valve annulus. In 7 of 9 animals, circumferential radiofrequency ablation lesions were applied periostially to ablate 11 pulmonary veins. In patients, all of the pulmonary veins were remotely electrically isolated in an extraostial fashion. Adjunctive ablation included superior vena cava isolation in 6 patients, cavotricuspid isthmus ablation in 5 patients, and ablation of sites of complex fractionated activity and atypical LA flutters in 3 patients. This study demonstrates the safety and feasibility of an emerging paradigm for atrial fibrillation ablation involving the confluence of 3 technologies: 3-dimensional imaging, electroanatomic mapping, and remote robotic navigation.
    Circulation 06/2007; 115(21):2705-14. · 15.20 Impact Factor
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    ABSTRACT: Irrigated-tip catheter ablation allows larger ablation lesions to be created, but also decreases catheter temperature monitoring accuracy. It is unclear which parameters should be monitored to optimize efficacy and safety during irrigated-tip ablation. Freshly excised hearts from eight male pigs were perfused and superfused using oxygenated swine blood in an ex vivo model. Ablations were performed for 1 minute using one of five different ablation protocols: (1) Temperature Control (42 degrees C 40 W), (2) Fixed Power 20 W, (3) Fixed Power 30 W, (4) Impedance Control (target 10 ohm impedance drop), and (5) Impedance Control (target 20 ohm drop). All ablations were performed with a perpendicular orientation of the catheter to the endocardial surface. Ablation lesions depth was significantly lower in the temperature control group (5.0 +/- 1.7 mm) compared with the fixed power ablation groups (6.5 +/- 1.0 mm for Power 20 W, 6.6 +/- 1.2 mm for Power 30 W). Impedance-controlled ablation created lesions intermediate in depth between fixed power and temperature controlled (6.0 +/- 1.6 for Impedance 10 ohms and 6.2 +/- 1.4 mm for Impedance 20 ohms groups). There was a significantly greater incidence of pops and thrombus formation in the Power 20 W (9/14), Power 30 W (10/14), and Impedance 20 ohms (10/16) groups than the Temperature Control (1/16) and Impedance control 10 ohms (2/16) groups. Temperature control improved the safety profile during irrigated-tip ablation in comparison with fixed-power ablations, but resulted in significantly smaller lesions. Impedance-controlled ablation lesions (target 10 ohm drop) created lesions of comparable size to fixed-power ablations with a significantly better safety profile.
    Journal of Cardiovascular Electrophysiology 04/2007; 18(3):318-25. · 3.48 Impact Factor
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    ABSTRACT: Preprocedural cardiac imaging (CT/MRI) and intraprocedural electroanatomical mapping (EAM) are commonly used during left atrial (LA) catheter ablation of atrial fibrillation (AF). In the optimal scenario, the imaging datasets would be directly integrated with the EAM system to guide catheter mapping based on the accurate individual cardiac anatomy. Strategies to align the EAM and imaging data were assessed by simulations using a life-size model of the LA and aorta. This revealed that the optimal strategy includes mapping both the aorta and LA. Respiratory changes in cardiac anatomy were evaluated by MR angiography performed in 10 patients during both inspiration and expiration. Comparison of paired images revealed inferior and anterior movement of the LA relative to the aorta with inspiration. Next, image integration was employed in a series of patients (n = 13) scheduled for AF catheter ablation. After preprocedural CT angiography (7 during inspiration and 6 during expiration), three-dimensional anatomical renderings of these images were integrated with the EAM data in a custom workstation to permit real-time catheter manipulation within these constructs. The electrophysiologist was blinded to these integrated images, but the accuracy of the process was assessed real-time by a second operator. This revealed poor alignment during inspiration but good alignment during expiration--the respiratory phase most closely resembling that during EAM. This study supports the feasibility of integrating preacquired cardiac images with real-time electroanatomical mapping to guide catheter movement in the LA in a reliable and clinically relevant manner.
    Journal of Cardiovascular Electrophysiology 12/2006; 17(11):1221-9. · 3.48 Impact Factor
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    ABSTRACT: Balloon ablation catheters using various energy sources are being developed to perform pulmonary vein (PV) isolation to treat atrial fibrillation. Prior evaluations of 2D CT/MR images are limited by the frequent elliptical shape of the PV ostia, the nonorthogonal orientation of the PVs to the left atrial (LA) chamber, and difficulty in appreciating through-slice curvature. To provide anatomical data relevant to balloon catheter ablation, 3D surface reconstructions of LA-PVs were generated and analyzed to define ostial architecture and size. Using MRI datasets obtained from 101 paroxysmal AF patients, the LA-PVs were segmented to generate 3D LA-PV surface reconstructions. Using both external and endoluminal projections, the PV ostial and antral regions were identified and evaluated. In the left PVs, a common left-sided ostium was identified in 94 patients, with an ostial circumference of 95 +/- 15 mm. Branching of the left PVs occurred 0-5 mm away from the common left ostium in 43 patients (43%), 5-15 mm away from the common os in 37 patients (37%), and >15 mm away from the common os in 14 patients (14%). In patients with either distinct left PV ostia, or common os <15 mm (87 patients), the individual LSPV/LIPV ostial circumferences were 67 +/- 12 mm and 58 +/- 9 mm, respectively. Mean left antral circumference was 114 +/- 17 mm. In the right PVs, the ostial circumferences of the RSPV/RIPV were 68 +/- 11 mm and 66 +/- 11 mm, respectively. Mean right antral circumference was 107 +/- 19 mm. Assuming ideal deformation of the LA chamber anatomy, the minimal diameters of a balloon ablation catheter required to isolate 95% of the RSPV, RIPV, LSPV, LIPV, LCPV, left antrum, and right antrum are 29 mm, 28 mm, 29 mm, 24 mm, 40 mm, 46 mm, and 47 mm, respectively. Analysis of 3D surface reconstructions of LA-PV anatomy reveals that balloon catheter-based ablation of the PVs is likely feasible in most patients, but balloon ablation of the common PV antra would be problematic.
    Journal of Cardiovascular Electrophysiology 04/2006; 17(3):251-5. · 3.48 Impact Factor
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    ABSTRACT: A potential complication during ablation of atrial fibrillation (AF) is damage to adjacent structures such as the esophagus and aorta. Fatal atrio-esophageal fistulas have developed after surgery- or catheter-based AF ablation procedures. The purpose of this study was to analyze multidetector computed tomography (MDCT) angiographic images to determine the anatomic relationship of the aorta and esophagus to the left atrium (LA). Sixty-five subjects underwent CT imaging using a 16-slice MDCT scanner: 24 with paroxysmal AF, 21 with chronic AF, and 20 "control" subjects without a history of AF. Measurements assessed included LA diameters, width of the esophagus and aorta in contact with the posterior LA wall, and distance from the esophagus to the four pulmonary veins (PVs), spine, and LA endocardium. Mean LA diameters were significantly larger in patients with AF vs the control group (P = .003 for anteroposterior diameter; P = .009 for transverse diameter). The anterior aspect of the esophagus was directly apposed to the LA in all cases (contact width 18.9 +/- 4.4 mm). The position of the esophagus varied in the posterior mediastinum but on average was closer to the ostia of the left PVs (P = .0001). The descending aorta was in contact with the LA and/or left PVs in 50 of 65 subjects. The esophagus was closer to the spine in the chronic AF vs control group (P = .007), likely due to increased LA dimension. In addition to its ability to assess PV anatomy, preprocedural MDCT imaging can investigate the variable relationship of adjacent structures, such as the esophagus and aorta to the LA and PVs.
    Heart Rhythm 01/2006; 2(12):1317-23. · 5.05 Impact Factor
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    ABSTRACT: Image-guided intervention using pre-acquired CT/MR 3-dimensional images is an emerging strategy for atrial fibrillation (AF) ablation but may be limited by its use of static images to depict dynamic physiology. The effect of biologic factors such as respiration on the left atrial-pulmonary venous (LA-PV) anatomy is not well understood but is likely to have important implications. Conventional CT/MR imaging is performed during an inspiratory breath-hold, while electroanatomical mapping (EAM) during "quiet" breathing approximates an expiratory breath-hold. This study examined the effects of respiration on LA-PV anatomy and the error introduced by respiration on the integration of EAM with 3D MR imaging. Pre-procedural MRI angiography was performed at both end-expiration (EXP) and end-inspiration (INSP) in 20 patients undergoing AF catheter ablation. 3D INSP and EXP surface reconstructions of the LA-PVs were compared. In selected pts, EAM data acquired during the ablation procedure (n=7) were integrated with the 3D MRI datasets. Qualitative assessment of the INSP and EXP 3D images revealed splaying of the PVs and reduction in PV caliber of the right-sided PVs during held inspiration. After aligning these two datasets, the average surface-to-surface distance calculated by region ranged from 1.99mm (right middle PV) to 3.79mm (left superior PV). Registration of the EAM to the MRI models was better for the EXP dataset (2.30+/-0.73mm) than the INSP dataset (3.03+/-0.57mm; p=0.004). There are significant changes in LA-PV anatomy with respiration. MR images acquired during standard held inspiration may introduce unnecessary errors in registration during image-guided intervention.
    Heart Rhythm 12/2005; 2(11):1173-8. · 5.05 Impact Factor
  • Circulation 08/2005; 112(2):e35-6. · 15.20 Impact Factor
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    ABSTRACT: In a series of in vitro and in vivo experiments, we evaluated the feasibility of integrating three-dimensional (3D) magnetic resonance imaging (MRI) and electroanatomic mapping (EAM) data to guide real-time left ventricular (LV) catheter manipulation. Substrate-based catheter ablation of post-myocardial infarction ventricular tachycardia requires delineation of the scarred myocardium, typically using an EAM system. Cardiac MRI might facilitate this procedure by localizing this myocardial scar. A custom program was employed to integrate 3D MRI datasets with real-time EAM. Initially, a plastic model of the LV was used to determine the optimal alignment/registration strategy. To determine the in vivo accuracy of the registration process, ablation lesions were directed at iatrogenic MRI-visible "targets" (iron oxide injections) within normal porcine LVs (n = 5). Finally, this image integration strategy was assessed in a porcine infarction model (n = 6) by targeting ablation lesions to the scar border. The in vitro experiments revealed that registration of the LV alone results in inaccurate alignment due primarily to rotation along the chamber's long axis. Inclusion of the aorta in the registration process rectified this error. In the iron oxide injection experiments, the ablation lesions were 1.8 +/- 0.5 mm from the targets. In the porcine infarct model, the catheter could be reliably navigated to the mitral valve annulus, and the ablation lesions were uniformly situated at the scar borders. These data suggest that registration of pre-acquired magnetic resonance images with real-time mapping is sufficiently accurate to guide LV catheter manipulation in a reliable and clinically relevant manner.
    Journal of the American College of Cardiology 01/2005; 44(11):2202-13. · 14.09 Impact Factor
  • Journal of The American College of Cardiology - J AMER COLL CARDIOL. 01/2004; 43(5).
  • Journal of The American College of Cardiology - J AMER COLL CARDIOL. 01/2004; 43(5).

Publication Stats

438 Citations
88.46 Total Impact Points

Institutions

  • 2008
    • Partners HealthCare
      Boston, Massachusetts, United States
    • The Police Academy of the Czech Republic in Prague
      Praha, Praha, Czech Republic
  • 2005–2008
    • Massachusetts General Hospital
      • Division of Cardiology
      Boston, Massachusetts, United States