Julianne H. Spencer

Human Coronary Venous Anatomy: Implications for Interventions

The coronary venous system is a highly variable network of veins that drain the deoxygenated blood from the myocardium. The system is made up of the greater cardiac system, which carries the majority of the deoxygenated blood to the right atrium, and the smaller cardiac system, which drains the blood directly into the heart chambers. The coronary veins are currently being used for several biomedical applications, including but not limited to cardiac resynchronization therapy, ablation therapy, defibrillation, perfusion therapy, and annuloplasty. Knowledge of the details of the coronary venous anatomy is essential for optimal development and delivery of treatments using this vasculature. This article is part of a JCTR special issue on Cardiac Anatomy.

A detailed assessment of the human coronary venous system using contrast computed tomography of perfusion-fixed specimens

BACKGROUND Access to the coronary venous system is required for the delivery of several cardiac therapies including cardiac resynchronization therapy, coronary sinus ablation, and coronary drug delivery. Therefore, characterization of the coronary venous anatomy will provide insights to gain improved access to these vessels and subsequently improved therapies. For example, cardiac resynchronization therapy has a 30% nonresponder rate, partially due to suboptimal lead placement within the coronary veins. OBJECTIVE To understand the implications of coronary venous anatomy for the development of devices deployed within these vessels. METHODS We cannulated the coronary sinus of 121 perfusion-fixed human hearts with a venogram balloon catheter and injected contrast into the venous system while obtaining computed tomographic images. For each major coronary vein, distance to the coronary sinus, branching angle, arc length, tortuosity, number of branches, and ostial diameter were assessed from the reconstructed anatomy. RESULTS Twenty-nine percent (35/121) specimens did not have a venous branch overlying the inferolateral side of the heart large enough to fit a 5F pacing lead. No significant differences in anatomy were found between subgroups with varying cardiac medical histories. CONCLUSION The anatomical approach employed in this study has allowed for the development of a unique database of human coronary venous anatomy that can be used for the optimization of design and delivery of cardiac devices.

Anatomical Reconstructions of the Human Cardiac Venous System using Contrast-computed Tomography of Perfusion-fixed Specimens

A detailed understanding of the complexity and relative variability within the human cardiac venous system is crucial for the development of cardiac devices that require access to these vessels. For example, cardiac venous anatomy is known to be one of the key limitations for the proper delivery of cardiac resynchronization therapy (CRT)(1) Therefore, the development of a database of anatomical parameters for human cardiac venous systems can aid in the design of CRT delivery devices to overcome such a limitation. In this research project, the anatomical parameters were obtained from 3D reconstructions of the venous system using contrast-computed tomography (CT) imaging and modeling software (Materialise, Leuven, Belgium). The following parameters were assessed for each vein: arc length, tortuousity, branching angle, distance to the coronary sinus ostium, and vessel diameter. CRT is a potential treatment for patients with electromechanical dyssynchrony. Approximately 10-20% of heart failure patients may benefit from CRT(2). Electromechanical dyssynchrony implies that parts of the myocardium activate and contract earlier or later than the normal conduction pathway of the heart. In CRT, dyssynchronous areas of the myocardium are treated with electrical stimulation. CRT pacing typically involves pacing leads that stimulate the right atrium (RA), right ventricle (RV), and left ventricle (LV) to produce more resynchronized rhythms. The LV lead is typically implanted within a cardiac vein, with the aim to overlay it within the site of latest myocardial activation. We believe that the models obtained and the analyses thereof will promote the anatomical education for patients, students, clinicians, and medical device designers. The methodologies employed here can also be utilized to study other anatomical features of our human heart specimens, such as the coronary arteries. To further encourage the educational value of this research, we have shared the venous models on our free access website: www.vhlab.umn.edu/atlas.

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.

The relative anatomy of the coronary arterial and venous systems: implications for coronary interventions.

An anatomical understanding of human coronary arterial and venous systems is necessary for device development and therapy applications that utilize these vessels. We investigated the unique use of contrast‐CT scans from perfusion‐fixed human hearts for three‐dimensional visualization and analysis of anatomical features of the coronary systems. The coronary arterial and venous systems of eleven perfusion‐fixed human hearts were modeled using contrast‐CT and Mimics software. The coronary arteries that coursed near the major coronary veins, how close coronary arteries were to coronary veins, and the size of adjacent coronary arteries were recorded and analyzed. The majority of coronary veins were within 5 mm of a coronary artery somewhere along its length. Interventricular veins elicited the largest occurrence of overlaps. There was significant variability in the percentage of each vein that coursed within 0.5, 1, 2, and 5 mm of a nearby artery. The left marginal veins and anterior interventricular vein had the largest portion of the vein that coursed near a coronary artery. The right coronary artery most often coursed near the middle cardiac vein. The inferior veins of the left ventricle elicited the most variation in adjacent arteries. The left circumflex artery and/or branches of the circumflex artery coursed near the left marginal vein in all cases where there was an artery near the marginal vein. The wide variation of measurements reinforces the importance of a precise understanding of individualized cardiac anatomy in order to provide the highest quality care to cardiac patients. Clin. Anat. 27:1023–1029, 2014.

Impact of generator replacement on the risk of Fidelis lead fracture

BACKGROUND A dilemma arises about the merits of conservative management vs lead replacement and/or extraction when patients with a Medtronic Sprint Fidelis lead undergo generator replacement. Conflicting reports suggest that the fracture rate may increase after generator change. OBJECTIVE The purpose of this study was to investigate the effect of generator replacement on Fidelis lead performance. METHODS The Carelink PLUS cohort is composed of 21,500 Fidelis leads (model 6949) implanted in 1,006 centers. The survival rate for leads that remained active after the first generator replacement was compared with that for a control group with matched lead implant duration, patient age, patient sex, and generator type using the Kaplan-Meier method. The control groups starting point was adjusted to match the implant duration of each lead in the replacement group to allow for the comparison of similarly aged leads. RESULTS Of the 2,988 implanted leads in each group, there was no statistical difference in the number of lead fractures between cases and controls (replacement, n = 227; no replacement, n = 257; Fisher exact, P = .169). Lead survival analysis demonstrated that lead performance since the first replacement procedure did not differ from that of the matched control group. CONCLUSION The Fidelis lead survival rate after generator replacement does not differ from that of the Fidelis leads that have not had replacement. In the event of generator replacement with no manifestation of lead fracture, the lead model, patient age and life expectancy, ejection fraction, comorbidities, ease of extraction, local extraction expertise, and patient preference should be considered to determine the best course of action.

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 Use of Isolated Heart Models and Anatomical Specimens as Means to Enhance the Design and Testing of Cardiac Devices

In recent years, the use of perfusion-fixed cadaveric specimens and isolated heart models has helped to develop an improved understanding of the device-tissue interface and has also contributed to the rapid evolution of surgically and percutaneously delivered cardiac therapies. This chapter describes a novel series of techniques utilized within the Visible Heart® laboratory by engineers, scientists, and anatomists to visualize and analyze the heart and assess potential repair or replacement therapies. The study of reanimated large mammalian hearts (including human hearts) and specially prepared anatomical specimens, using various clinical and nonclinical imaging modalities, has provided feedback for design engineers and clinicians that seek to develop and/or employ cardiac therapies for patients with acquired or congenital heart disease.