Ryan P. Goff

In vitro assessment of induced phrenic nerve cryothermal injury

BACKGROUND Phrenic nerve injury, both left and right, is considered a significant complication of cryoballoon ablation for treatment of drug-refractory atrial fibrillation, and functional recovery of the phrenic nerve can take anywhere from hours to months. OBJECTIVE The purpose of this study was to focus on short periods of cooling to determine the minimal amount of cooling that may terminate nerve function related to cryo ablation. METHODS Left and/or right phrenic nerves were dissected from the pericardium and connective tissue of swine (n = 35 preparations). Nerves were placed in a recording chamber modified with a thermocouple array. This apparatus was placed in a digital water bath to maintain an internal chamber temperature of 37°C. Nerves were stimulated proximally with a 1-V, 0.1-ms square wave. Bipolar compound action potentials were recorded proximal and distal to the site of ablation both before and after ablation, then analyzed to determine changes in latency, amplitude, and duration. Temperatures were recorded at a rate of 5 Hz, and maximum cooling rates were calculated. RESULTS Phrenic nerves were found to elicit compound action potentials upon stimulation for periods up to 4 hours minimum. Average conduction velocity was 56.7 ± 14.7 m/s preablation and 49.8 ± 16.6 m/s postablation (P = .17). Cooling to mild subzero temperatures ceased production of action potentials for >1 hour. CONCLUSION Taking into account the data presented here, previous publications, and a conservative stance, during cryotherapy applications, cooling of the nerve to below 4°C should be avoided whenever possible.

Imaging of a Coronary Artery Stent Implantation Within an Isolated Human Heart

Currently, over 16 million Americans have coronary artery disease (CAD). Consequently, almost eight million Americans have suffered a myocardial infarction (MI). One method of treating CAD and MI is the implantation of an expandable stent within a compromised artery (for example, one partially occluded by atherosclerotic plaque). In 2007 alone, approximately 560,000 Americans received a coronary stent implantation [1]. Novel imaging of the implantation of a coronary artery stent has potential educational benefits for physicians, design engineers, and patients to better understand such procedures and the devices. We employed Visible Heart® methodologies [2] to obtain endoscopic footage of a coronary artery stent implantation within a reanimated human heart. This experimental approach provides unique imaging of the device–tissue interface that can be used for device development to address related issues, such as vessel perforation and stent dislodgement, which cannot be seen as well on fluoroscopy. The endoscopic imaging modality can then be used to evaluate emerging stent technologies. Furthermore, such images could be employed as useful training tools for cardiac interventionalists as well as educational means for explaining these procedures to patients. Method

Left phrenic nerve anatomy relative to the coronary venous system: Implications for phrenic nerve stimulation during cardiac resynchronization therapy

The objective of this study was to quantitatively characterize anatomy of the human phrenic nerve in relation to the coronary venous system, to reduce undesired phrenic nerve stimulation during left‐sided lead implantations. We obtained CT scans while injecting contrast into coronary veins of 15 perfusion‐fixed human heart‐lung blocs. A radiopaque wire was glued to the phrenic nerve under CT, then we created three‐dimensional models of anatomy and measured anatomical parameters. The left phrenic nerve typically coursed over the basal region of the anterior interventricular vein, mid region of left marginal veins, and apical region of inferior and middle cardiac veins. There was large variation associated with the average angle between nerve and veins. Average angle across all coronary sinus tributaries was fairly consistent (101.3°–111.1°). The phrenic nerve coursed closest to the middle cardiac vein and left marginal veins. The phrenic nerve overlapped a left marginal vein in >50% of specimens. Clin. Anat. 28:621–626, 2015.

Direct visualization of induced steam pops during radiofrequency ablation

Introduction Importantly, during clinical ablation procedures, the elicitation of elevated tissue temperatures may induce audible steam pops. Rapidly induced high endocardial tissue temperatures are considered to generate these events as a result of blood/tissue vaporizations. In addition, discrepancies between monitored catheter tip temperature and actual endocardial tissue temperature may be related to the unanticipated elicitation of steam pops. Ultimately, these induced tissue disruptions can have important clinical consequences. They even may result in perforations of the atrial wall and/or the release of tissue or air emboli from the affected tissues.

Cardiac remodeling as a consequence of atrial fibrillation： An anatomical study of perfusion-fixed human heart specimens

Background Atrial fibrillation (AF) causes a continuum of atrial anatomical remodeling. Methods Using a library of perfusion-fixed human hearts, specimens with AF were compared to controls. During this preliminary assessment study, direct measurements were taken of atrial volume, pulmonary vein (PV) circumference, and left atrial (LA) wall thicknesses. Results Hearts with AF typically had larger atrial volumes, as well as a much larger variation in volume compared to controls (range of 59.6–227.1 mL in AF hearts compared to 65.1–115.9 mL in controls). For all hearts, right PVs were larger than left PVs (mean: 171.4 ± 84.6 mm[2] for right and 118.2 ± 50.1 mm[2] for left, P < 0.005). LA wall thicknesses ranged from 0.7 mm to 3.1 mm for both AF and control hearts. Conclusions Hearts with AF had a large range of sizes which is consistent with the progression of atrial remodeling during AF. The large range of thicknesses will influence the amount of energy needed to create transmural lesions during ablation procedures.

The benefits of the Atlas of Human Cardiac Anatomy website for the design of cardiac devices

This paper describes how the Atlas of Human Cardiac Anatomy website can be used to improve cardiac device design throughout the process of development. The Atlas is a free-access website featuring novel images of both functional and fixed human cardiac anatomy from over 250 human heart specimens. This website provides numerous educational tutorials on anatomy, physiology and various imaging modalities. For instance, the ‘device tutorial’ provides examples of devices that were either present at the time of in vitro reanimation or were subsequently delivered, including leads, catheters, valves, annuloplasty rings and stents. Another section of the website displays 3D models of the vasculature, blood volumes and/or tissue volumes reconstructed from computed tomography and magnetic resonance images of various heart specimens. The website shares library images, video clips and computed tomography and MRI DICOM files in honor of the generous gifts received from donors and their families.

The Path of a Pulmonary Artery Catheter Visualized through a Beating Human Heart

Pulmonary artery (PA) catheters can be positioned within a patient via access through the right side of the heart, for diagnostic and monitoring purposes. Data obtained include PA, right atrial, and left atrial pressures, cardiac outputs, and samples of mixed venous blood. Such catheters are typically placed with the aid of their distal inflatable balloon and by sensed catheter pressures—thus, placed without fluoroscopy. Here we obtained novel videoscopic imaging of a PA catheter insertion by employing visible heart methodologies (1). Specifically, in a reanimated, nonviable donor human heart (male, 45 yr old), eliciting a native sinus rhythm, functioning in a fourchamber working mode, the use of a clear perfusate allowed for this visualization, while fluoroscopic images were also captured concurrently (not continuously). Note that the catheter’s balloon was filled with fluoroscopic contrast to enhance visualization (see video in the online supplement). Associated pressure tracings and computer animations were synchronized appropriately with the catheter delivery. Of note, the “wedge“ pressure, defined as a drop in pressure when the balloon totally occludes the PA (Figure 1), was simulated by partially ligating a distal portion of this heart’s remaining PA (i.e., this was near the outflow cannula, thus the wedge position appears much more proximal than would be found in vivo, which would be within a lung). See also the Pulmonary Artery Catheter Education Project (www.pacep.org) for additional theoretical and educational information.

Direct visualization of an iatrogenic septal defect in a reanimated human heart

Support was provided by a research contract with Medtronic, Inc and a grant from the Dr Earl E. Bakken family for promotion of heart–brain research. These funding sources had no involvement in study design, data collection/analysis/interpretation, report writing, or the decision to submit for publication. Address reprint requests and correspondence: Paul Iaizzo, PhD, FHRS, University of Minnesota, 420 Delaware St SE, B172 Mayo, MMC 195, Minneapolis, MN 55455. E-mail address: iaizz001@umn.edu.

Localized Drug Delivery for Cardiothoracic Surgery

It is noteworthy to consider that extensive bioavailability and bioequivalence studies are typically required before new drug therapies can be approved [1]. These studies include pharmacokinetic studies that take into account: 1) dosing, absorption, and elimination rates of the drug and its active metabolites, as well as 2) the potential effects of multiple doses, drug interactions, and the differences whether medications are taken with or without food. A major therapeutic factor that compounds the variations often seen from patient to patient is individual differences in absorption and elimination rates. This will also cause variations in the amount of drug that reaches the desired targeted tissue when used as a clinical therapy.