Mechanisms of cardiac and renal dysfunction in patients dying of sepsis.

RATIONALE: The mechanistic basis for cardiac and renal dysfunction in sepsis is unknown. In particular, the degree and type of cell death is undefined. OBJECTIVES: To evaluate the degree of sepsis-induced cardiomyocyte and renal tubular cell injury and death. METHODS: Light and electron microscopy and immunohistochemical staining for markers of cellular injury and stress, including connexin-43 and kidney-injury-molecule-1 (Kim-1), were used in this study. MEASUREMENTS AND MAIN RESULTS: Rapid postmortem cardiac and renal harvest was performed in 44 septic patients. Control hearts were obtained from 12 transplant and 13 brain-dead patients. Control kidneys were obtained from 20 trauma patients and eight patients with cancer. Immunohistochemistry demonstrated low levels of apoptotic cardiomyocytes (<1-2 cells per thousand) in septic and control subjects and revealed redistribution of connexin-43 to lateral membranes in sepsis (P < 0.020). Electron microscopy showed hydropic mitochondria only in septic specimens, whereas mitochondrial membrane injury and autophagolysosomes were present equally in control and septic specimens. Control kidneys appeared relatively normal by light microscopy; 3 of 20 specimens showed focal injury in approximately 1% of renal cortical tubules. Conversely, focal acute tubular injury was present in 78% of septic kidneys, occurring in 10.3 ± 9.5% and 32.3 ± 17.8% of corticomedullary-junction tubules by conventional light microscopy and Kim-1 immunostains, respectively (P < 0.01). Electron microscopy revealed increased tubular injury in sepsis, including hydropic mitochondria and increased autophagosomes. CONCLUSIONS: Cell death is rare in sepsis-induced cardiac dysfunction, but cardiomyocyte injury occurs. Renal tubular injury is common in sepsis but presents focally; most renal tubular cells appear normal. The degree of cell injury and death does not account for severity of sepsis-induced organ dysfunction.

Right ventricular arrhythmogenesis in failing human heart: the role of conduction and repolarization remodeling.

Increased dispersion of repolarization has been suggested to underlie increased arrhythmogenesis in human heart failure (HF). However, no detailed repolarization mapping data were available to support the presence of increased dispersion of repolarization in failing human heart. In the present study, we aimed to determine the existence of enhanced repolarization dispersion in the right ventricular (RV) endocardium from failing human heart and examine its association with arrhythmia inducibility. RV free wall preparations were dissected from five failing and five nonfailing human hearts, cannulated and coronary perfused. RV endocardium was optically mapped from an ∼6.3 × 6.3 cm(2) field of view. Action potential duration (APD), dispersion of APD, and conduction velocity (CV) were quantified for basic cycle lengths (BCL) ranging from 2,000 ms to the functional refractory period. We found that RV APD was significantly prolonged within the failing group compared with the nonfailing group (560 ± 44 vs. 448 ± 39 ms, at BCL = 2,000 ms, P < 0.05). Dispersion of APD was increased in three failing hearts (161 ± 5 vs. 86 ± 19 ms, at BCL = 2,000 ms). APD alternans were induced by rapid pacing in these same three failing hearts. CV was significantly reduced in the failing group compared with the nonfailing group (81 ± 11 vs. 98 ± 8 cm/s, at BCL = 2,000 ms). Arrhythmias could be induced in two failing hearts exhibiting an abnormally steep CV restitution and increased dispersion of repolarization due to APD alternans. Dispersion of repolarization is enhanced across the RV endocardium in the failing human heart. This dispersion, together with APD alternans and abnormal CV restitution, could be responsible for the arrhythmia susceptibility in human HF.

Quatrefoil reentry caused by burst pacing.

BACKGROUND: Experiments and clinical studies have shown that high-frequency (burst) pacing can induce reentry and fibrillation without a strong shock. We hypothesize that a train of weak stimuli induces quatrefoil reentry, and investigate the mechanism and threshold for this mode of reentry induction. METHODS: We apply a train of weak stimuli at different pacing rates to determine the threshold necessary to induce quatrefoil reentry. Numerical calculations are used to simulate cardiac tissue, based on the bidomain model with unequal anisotropy ratios. We consider both anodal and cathodal stimuli. RESULTS: Quatrefoil reentry is initiated using much smaller currents during burst pacing (0.9 mA) compared to a single premature pulse (8.6 mA). As we varied the pacing rate, we observed reentry at the border between different modes of phase locking, such as between 1:1 and 2:1 responses. CONCLUSION: Burst pacing can significantly reduce the threshold for reentry. However, the extreme sensitivity of reentry induction to the exact number of stimuli in the pulse train makes the method difficult to use as a consistent, reproducible way to induce reentry.

Averaging over depth during optical mapping of unipolar stimulation.

Numerical simulations have predicted the distribution of transmembrane potential during electrical stimulation of cardiac tissue. When comparing these predictions to measurements obtained using optical mapping techniques, the optical signal should not be compared to the transmembrane potential calculated at the surface of the tissue, but instead to the transmembrane potential averaged over depth. In this paper, the bidomain model is used to calculate the transmembrane potential in a three-dimensional slab of cardiac tissue, stimulated by a unipolar electrode on the tissue surface. For an optical decay constant of 0.3 mm and an electrode radius of 1 mm, the surface transmembrane potential is more than a factor of three larger than the transmembrane potential averaged over depth. Our results suggest that optical mapping underestimates the surface transmembrane potential during electrical stimulation.

How to build an integrated biobank: the Washington University Translational Cardiovascular Biobank & Repository experience.

Translational studies that assess and extend observations made in animal models of human pathology to elucidate relevant and important determinants of human diseases require the availability of viable human tissue samples. However, there are a number of technical and practical obstacles that must be overcome in order to perform cellular and electrophysiological studies of the human heart. In addition, changing paradigms of how diseases are diagnosed, studied and treated require increasingly complex integration of rigorous disease phenotyping, tissue characterization and detailed delineation of a multitude of "_omics". Realizing the need for quality-controlled human cardiovascular tissue acquisition, annotation, biobanking and distribution, we established the Translational Cardiovascular Biobank & Repository at Washington University School of Medicine. Several critical details are essential for the success of cardiovascular biobanking including coordinated, trained and dedicated staff members; adequate, nonrestrictive informed consent protocols; and fully integrated clinical data management applications for annotating, tracking and sharing of tissue and data resources. Labor and capital investments into growing biobanking resources will facilitate collaborative efforts aimed at limiting morbidity and mortality due to heart disease and improving overall cardiovascular health.

Simulations of optical mapping during electroporation.

Experiments using optical mapping suggest that electroporation occurs in cardiac tissue when the transmembrane potential, Vm, is observed to be significantly less than +/- 400 mV. Our hypothesis, which we test by numerical simulation, is that Vm is greater than +/- 400 mV at the tissue surface, but optical mapping underestimates Vm because it averages over depth. Results indicate a significant underestimation of Vm. Experimental studies indicate a depolarization of the resting transmembrane potential, Vrest, after a strong shock. In a homogeneous model, electroporation only occurs near the tissue surface. Just as Vm during the stimulus is underestimated due to averaging, we hypothesize that the depolarization of Vrest is also underestimated.