Michael D. Diodato

Physiological consequences of bipolar radiofrequency energy on the atria and pulmonary veins: a chronic animal study

BACKGROUND Alternative energy sources have been proposed for the transvenous and surgical treatment of atrial fibrillation. This study examined the physiologic consequences of a novel energy source, bipolar radiofrequency energy, in a chronic animal model in order to determine its ability to produce transmural lesions on the beating heart. METHODS Five dogs underwent baseline pacing from the following target areas: right and left atrial appendage, superior and inferior vena cavae, and right and left pulmonary veins. A cuff of atrial myocardium, proximal to the target tissue was clamped and ablated between the arms of the bipolar radiofrequency energy device. Tissue conductance was used as a transmural indicator. After ablation, the pacing protocol was repeated. Baseline and postablation pulmonary vein flows were measured. Animals were survived for 30 days, and permanent electrical isolation was evaluated by pacing, epicardial mapping, and histology. RESULTS Mean ablation time was 5.0 +/- 1.8 seconds and mean peak tissue temperature was 46.7 degrees C +/- 2.8 degrees C. All lesions (30/30) acutely and permanently isolated atrial tissue. There was no change in pulmonary vein flow. Mapping studies with pacing of atrial tissue on both sides of the lesion confirmed isolation. Histology demonstrated that all lesions were linear, continuous, and transmural with no thrombus formation or stenosis. CONCLUSIONS Bipolar radiofrequency energy rapidly produced permanent transmural linear lesions on the beating heart. Measurement of tissue conductance reliably predicted transmural lesions. This new technology may enable the development of a less invasive, surgical approach to atrial fibrillation.

Robotic cardiac surgery: overview

Most endoscopic procedures are excisional, not reconstructive or microsurgical, mostly because conventional endoscopic instrumentation lacks dexterity due to long, nonarticulated instruments, a fixed pivot point and counterintuitive movement of the instrument tip, and lack of depth perception. Endoscopic approaches to cardiac surgery have not been successful; however, the development of robotic surgical systems has overcome many limitations of endoscopy. Computer-assisted surgery has created a computerized digital interface between the surgeons hands and surgical instrument tips and enhances surgical ability, thereby enabling endoscopic microsurgery. Recently, robotic systems have allowed cardiac surgeons to perform minimally invasive endoscopic coronary artery bypass grafting (CABG) and valve procedures. This article summarizes the use of robotics in cardiac surgery and discusses its potential in our specialty.

Coronary Artery Bypass Graft Surgery: The Past, Present, and Future of Myocardial Revascularisation

The development of the heart-lung machine ushered in the era of modern cardiac surgery. Coronary artery bypass graft surgery (CABG) remains the most common operation performed by cardiac surgeons today. From its infancy in the 1950s till today, CABG has undergone many developments both technically and clinically. Improvements in intraoperative technique and perioperative care have led to CABG being offered to a more broad patient profile with less complications and adverse events. Our review outlines the rich history and promising future of myocardial revascularization.

Dose Response Curves for Microwave Ablation in the Cardioplegia-Arrested Porcine Heart

INTRODUCTION Microwave ablation has been used clinically for the surgical treatment of atrial fibrillation, particularly during valve procedures. However, dose- response curves have not been established for this surgical environment. The purpose of this study was to examine dosimetry curves for the Flex 4 and Flex 10 microwave devices in an acute cardioplegia-arrested porcine model. METHODS Twelve domestic pigs (40-45 kg) were acutely subjected to Flex 4 (n = 6) and Flex 10 (n = 6) ablations. On a cardioplegically arrested heart maintained at 10-15(o)C, six endocardial atrial and seven epicardial ventricular lesions were created in each animal. Ablations were performed for 15 s, 30 s, 45 s, 60 s, 90 s, 120 s, and 150 s (65 W, 2.45 GHz). The tissue was stained with 2,3,5-triphenyl-tetrazolium chloride and lesions were sectioned at 5 mm intervals. Lesion depth and width were determined from digital photomicrographs of each lesion (resolution +/- .03 mm). RESULTS Average atrial thickness was 2.88 +/- .4 mm (range 1.0 to 8.0 mm). 94% of ablated atrial sections created by the FLEX 4 (n = 16) and the FLEX 10 (n = 16) were transmural at 45 seconds. 100% of atrial sections were transmural at 90 seconds with the FLEX 10 (n = 14) and at 60 seconds with the Flex 4 device (n = 15). Lesion width and depth increased with duration of application. CONCLUSION Both devices were capable of producing transmural lesions on the cardioplegically arrested heart at 65 W. These curves will allow surgeons to ensure transmural ablation by tailoring energy delivery to the specific atrial geometry.

Heat Shock Protein Expression During Cardiac Surgery

There has been a great deal of interest in a group of cellular proteins collectively called heat shock proteins (HSPs) to identify their role in the inflammatory and cell-mediated responses that occur during heart surgery [1]. Although most patients do fine after cardiopulmonary bypass (CPB), some develop an inflammatory response clinically resembling a sepsis-like state. At the cellular level, several stressrelated proteins, clustered as HSPs, participate in the inflammatory cascade mostly by acting as chaperons. Their basic role is to maintain the structural integrity of proteins under stress states by keeping them in their folded state, but their overexpression can lead to an inflammatory response. The ex vivo environment created during CPB exposes blood to nonendothelial circuitry, thereby triggering responses in the complement, coagulation, and humoral cascades. Chaperone HSPs play a significant role in inciting and modulating these triggers and responses. HSP-60, for example, is mostly intracellular; but in stress states it is overexpressed on endothelial cells. This protein is taken up by macrophages, which in turn cause it to trigger the immune system by signaling T and B lymphocytes. An HSP-60 lipopolysaccharide (LPS) complex then activates dendritic cells, causing release of interferon-c (INFc) and interleukin-12 (IL-12). This complex depends on toll-like receptors (TLRs) to gain entry into the cell via CD14 receptors. TLR 2, along with HSP-60, causes a T-cell response that down-regulates the secretion of tumor necrosis factor-a (TNFa) and INF c and up-regulates the secretion of transforming growth factor-b (TGFb) and IL-10. Intracellularly, the HSP60–LPS complex assembles nuclear factor jB (NF-jB) components, which in turn lead to initiation of cytokines, chemokines, and growth factor synthesis. This cascade leads to the hyperdynamic sepsislike syndrome sometimes seen following CPB. The HSP-70s are yet another complex set of proteins that include HSP-73, HSP-72, HSP-70 (which is stress inducible), and HSP70L1. This HSP family, however, is protective in nature. In stress states, HSP-70 enters the nucleus and activates poly (ADP-ribose) polymerase enzyme, involved in DNA repair. Overexpression of the latter enzyme can cause cellular energy depletion by overconsumption of ATP and NAD? often seen after rapid reperfusion. The deleterious effects of poly (ADP-ribose) polymerase can be neutralized by HSP-70 synthesized by inducing heat shock. This family of proteins also stabilizes the membranes of lysosomes, thereby preventing autolysis and apoptosis. HSP-70 is released into the extracellular compartment and also uses the CD-14 receptor along with TLR-2 and TLR-4 to stimulate nucleic synthesis of NK-jB, ultimately leading to monocyte stimulation. HSP70 is detected after cardiac surgery and more so during myocardial damage wherein high expression correlates with high creatine kinase, myocardial bound (CK-MB) and troponin-T levels. Its expression peaks 2 h after surgery and is fourfold lower during off-pump heart surgery compared to on-pump heart surgery. This is unlike HSP-60 levels, which seem to be unaffected regardless of whether CPB is used [2]. Other proteins that are increased during CPB include HSP-27, which prevents apoptosis by halting activation of caspase through sequestering cytochrome c and procaspase 3 and by stabilizing the cytoskeleton. Its levels rise with stress and decline when stress is attenuated; and it is increased twofold with use of CPB. HSP-90a is another A. Z. Chaudhry M. D. Diodato M. G. Massad (&) Division of Cardiothoracic Surgery, University of Illinois at Chicago, 840 S. Wood Street, CSB Suite 417(MC 958), Chicago, IL 60612, USA e-mail: mmassad@uic.edu

Current and future therapy for pulmonary hypertension in patients with right and left heart failure

Pulmonary hypertension (PH) is a devastating condition that without proper management can deteriorate progressively. Elevated pulmonary artery pressure without an identifiable etiology is called IPAH. PH resulting from a specific disease is referred to as secondary PH; left-sided cardiac disease can lead to an increase in pulmonary artery pressure resulting in increased vascular resistance and subsequent structural remodeling. If left-sided failure progresses to right-sided failure with high pulmonary artery pressure, the outcome is ominous. It has been clearly proven that early diagnosis and effective medical therapy can markedly decrease morbidity and mortality. In this review, we discuss the current treatment modalities and their limitations for PH secondary to heart failure. Conventional therapy in patients with pulmonary arterial hypertension as well as recent advances in the medical management of PH in general, are also described. Last, the surgical management of these patients and other promising interventional modalities are reviewed.