Electrical storm in patients with left ventricular assist devices: Risk factors, incidence, and impact on survival.

BACKGROUND: Ventricular arrhythmias (VAs) and electrical storm (ES) are recognized complications following left ventricular assist device (LVAD) implantation; however, their association with long term-outcomes remains poorly understood. OBJECTIVE: The purpose of this study was to describe the clinical impact of ES in a population of patients undergoing LVAD implantation at a quaternary care center in the United States. METHODS: This was an observational retrospective study of patients undergoing LVAD implantation from 2009 to 2020 at Duke University Hospital. The incidence of ES (≥3 sustained VA episodes over a 24-hour period without an identifiable reversible cause) was determined from patient records. Risk factors for ES were identified using multivariable Cox proportional hazards modeling. RESULTS: Among 730 patients undergoing LVAD implant, 78 (10.7%) developed ES at a median of 269 (interquartile range [IQR] 7-766) days following surgery. Twenty-seven patients (34.6%) developed ES within 30 days, while 51 (65.4%) presented with ES at a median 639 (IQR 281-1017) days after implant. Following ES, 41% of patients died within 1 year. Patients who developed ES were more likely to have a history of VAs, ventricular tachycardia ablation, antiarrhythmic drug use, and perioperative mechanical circulatory support around the time of LVAD implant than patients without ES. CONCLUSION: ES occurs in 1 in 10 patients after LVAD and is associated with higher mortality. Risk factors for ES include a history of VAs, VT ablation, antiarrhythmic drug use, and perioperative mechanical circulatory support. Optimal management of ES surrounding LVAD implant, including escalation of medical therapy, catheter ablation, or adjunctive sympatholytic therapies, remains uncertain.

Cardiac Implantable Electronic Devices: A Window Into the Evolution of Conduction Disease in Cardiac Amyloidosis.

OBJECTIVES: This study characterized the relationship between conduction disease and cardiac amyloidosis (CA) through longitudinal analysis of cardiac implantable electronic device (CIED) data. BACKGROUND: Bradyarrhythmias and tachyarrhythmias are commonly reported in CA and may precede a CA diagnosis, although the natural history of conduction disease in CA is not well-described. METHODS: Patients with CA (transthyretin amyloidosis cardiomyopathy [ATTR-CM] and light-chain amyloidosis [AL-CA]) and a CIED were identified within the Duke University Health System. Patient characteristics at the time of implantation, including demographics and data relevant to CA diagnosis, cardiac imaging, and CIED were recorded. CIED interrogations were analyzed for pacing and atrial fibrillation (AF) burden, activity level, lead parameters, and ventricular arrhythmia incidence and/or therapy. RESULTS: Thirty-four patients with CA (7 with AL-CA, 27 with ATTR-CM [78% with wild-type]; 82% men) with median age of 75 years and a mean ejection fraction of 42 ± 13% had a CIED implanted for bradycardia (65%) or prevention of sudden cardiac death (35%). CIED implantation preceded CA diagnosis in 14 patients (41%). Over a mean follow-up of 3.1 ± 4.0 years, right ventricular sensing amplitudes decreased but did not result in device malfunction; lead impedances and capture thresholds remained stable. Between post-implantation years 1 and 5, mean ventricular pacing increased from 56 ± 9% to 96 ± 1% (p = 0.003) and AF burden increased from 2 ± 1.3 to 17 ± 3 h/day (p = 0.0002). Ventricular arrhythmias were common (mean episodes per patient per year: 6.7 ± 2.3 [ATTR-CM] and 5.1 ± 3.2 [AL-CA]) but predominately nonsustained; only 1 patient with AL-CA required implantable cardioverter-defibrillator therapy. CONCLUSIONS: Longitudinal analysis of CIED data in patients with CA revealed progressive conduction disease, with high AF burden and eventual dependence on ventricular pacing, although lead parameters remained stable. Ventricular arrhythmias were common but predominantly nonsustained, particularly in ATTR-CM.

A care pathway for the cardiovascular complications of COVID-19: Insights from an institutional response.

The infection caused by severe acute respiratory syndrome coronavirus-2, or COVID-19, can result in myocardial injury, heart failure, and arrhythmias. In addition to the viral infection itself, investigational therapies for the infection can interact with the cardiovascular system. As cardiologists and cardiovascular service lines will be heavily involved in the care of patients with COVID-19, our division organized an approach to manage these complications, attempting to balance resource utilization and risk to personnel with optimal cardiovascular care. The model presented can provide a framework for other institutions to organize their own approaches and can be adapted to local constraints, resource availability, and emerging knowledge.

Outcomes following cardioversion for patients with cardiac amyloidosis and atrial fibrillation or atrial flutter.

Atrial arrhythmias commonly occur in patients with cardiac amyloidosis (CA), but there is limited data on safety or efficacy of cardioversion (DCCV) for management of these rhythms in CA. We identified 25 patients with CA (20 with transthyretin (TTR) and 5 with light-chain (AL) amyloidosis) at Duke University who underwent DCCV for atrial arrhythmias and documented procedural success, complications, and long-term morbidity and mortality. While DCCV successfully restored sinus rhythm in 96% of patients, 36% of patients experienced immediate procedural complications (primarily bradycardia and hypotension), 80% had recurrence of atrial arrhythmias at 1 year, and 52% died at 3 years, highlighting short-term safety concerns, long-term inefficacy, and poor prognosis associated with symptomatic atrial arrhythmias requiring DCCV in CA.

Cardiac Arrest in the Setting of Diffuse Coronary Ectasia: Perspectives on a Unique Ischemic Insult.

A 69-year-old man with a history of coronary artery ectasia, potentially resulting from an underlying heritable connective tissue disorder, presented with ventricular fibrillation. Despite medical management of ischemia, he developed recurrent ventricular tachycardia with poor neurological recovery. We highlight challenges in the management of coronary artery ectasia. (Level of Difficulty: Beginner.).

The passive properties of muscle fibers are velocity dependent.

The passive properties of skeletal muscle play an important role in muscle function. While the passive quasi-static elastic properties of muscle fibers have been well characterized, the dynamic visco-elastic passive behavior of fibers has garnered less attention. In particular, it is unclear how the visco-elastic properties are influenced by lengthening velocity, in particular for the range of physiologically relevant velocities. The goals of this work were to: (i) measure the effects of lengthening velocity on the peak stresses within single muscle fibers to determine how passive behavior changes over a range of physiologically relevant lengthening rates (0.1-10Lo/s), and (ii) develop a mathematical model of fiber viscoelasticity based on these measurements. We found that passive properties depend on strain rate, in particular at the low loading rates (0.1-3Lo/s), and that the measured behavior can be predicted across a range of loading rates and time histories with a quasi-linear viscoelastic model. In the future, these results can be used to determine the impact of viscoelastic behavior on intramuscular stresses and forces during a variety of dynamic movements.

Computational models predict larger muscle tissue strains at faster sprinting speeds.

INTRODUCTION: Proximal biceps femoris musculotendon strain injury has been well established as a common injury among athletes participating in sports that require sprinting near or at maximum speed; however, little is known about the mechanisms that make this muscle tissue more susceptible to injury at faster speeds. PURPOSE: This study aimed to quantify localized tissue strain during sprinting at a range of speeds. METHODS: Biceps femoris long head (BFlh) musculotendon dimensions of 14 athletes were measured on magnetic resonance (MR) images and used to generate a finite-element computational model. The model was first validated through comparison with previous dynamic MR experiments. After validation, muscle activation and muscle-tendon unit length change were derived from forward dynamic simulations of sprinting at 70%, 85%, and 100% maximum speed and used as input to the computational model simulations. Simulations ran from midswing to foot contact. RESULTS: The model predictions of local muscle tissue strain magnitude compared favorably with in vivo tissue strain measurements determined from dynamic MR experiments of the BFlh. For simulations of sprinting, local fiber strain was nonuniform at all speeds, with the highest muscle tissue strain where injury is often observed (proximal myotendinous junction). At faster sprinting speeds, increases were observed in fiber strain nonuniformity and peak local fiber strain (0.56, 0.67, and 0.72 for sprinting at 70%, 85%, and 100% maximum speed). A histogram of local fiber strains showed that more of the BFlh reached larger local fiber strains at faster speeds. CONCLUSIONS: At faster sprinting speeds, peak local fiber strain, fiber strain nonuniformity, and the amount of muscle undergoing larger strains are predicted to increase, likely contributing to the BFlh muscle's higher injury susceptibility at faster speeds.

The effects of aponeurosis geometry on strain injury susceptibility explored with a 3D muscle model.

In the musculoskeletal system, some muscles are injured more frequently than others. For example, the biceps femoris longhead (BFLH) is the most commonly injured hamstring muscle. It is thought that acute injuries result from large strains within the muscle tissue, but the mechanism behind this type of strain injury is still poorly understood. The purpose of this study was to build computational models to analyze the stretch distributions within the BFLH muscle and to explore the effects of aponeurosis geometry on the magnitude and location of peak stretches within the model. We created a three-dimensional finite element (FE) model of the BFLH based on magnetic resonance (MR) images. We also created a series of simplified models with a similar geometry to the MR-based model. We analyzed the stretches predicted by the MR-based model during lengthening contractions to determine the region of peak local fiber stretch. The peak along-fiber stretch was 1.64 and was located adjacent to the proximal myotendinous junction (MTJ). In contrast, the average along-fiber stretch across all the muscle tissue was 0.95. By analyzing the simple models, we found that varying the dimensions of the aponeuroses (width, length, and thickness) had a substantial impact on the location and magnitude of peak stretches within the muscle. Specifically, the difference in widths between the proximal and distal aponeurosis in the BFLH contributed most to the location and magnitude of peak stretch, as decreasing the proximal aponeurosis width by 80% increased peak average stretches along the proximal MTJ by greater than 60% while slightly decreasing stretches along the distal MTJ. These results suggest that the aponeurosis morphology of the BFLH plays a significant role in determining stretch distributions throughout the muscle. Furthermore, this study introduces the new hypothesis that aponeurosis widths may be important in determining muscle injury susceptibility.

Perivascular cells along venules upregulate NG2 expression during microvascular remodeling.

OBJECTIVE: Recently the authors have shown that neuron-glial antigen 2 (NG2) is expressed by perivascular cells along arterioles and capillaries, but not along venules in quiescent rat mesenteric microvascular networks. To investigate how the spatial distribution of this proteoglycan changes during microvascular remodeling, the objective of this study was to characterize the expression of NG2 in adult rat mesenteric microvascular networks undergoing active remodeling. METHODS: The distribution of NG2 expression was evaluated in adult rat mesenteric microvascular networks. Tissues were harvested from 250 g, female, Sprague-Dawley rats at 1, 3, and 5 days poststimulation and double immunolabeled for NG2 and CD31 (endothelial cell marker). RESULTS: After 1 day, NG2 expression was observed along 27 +/- 11% of network draining venules (14-55 microm) and after 3 days, 59 +/- 10% of draining venules (13-59 microm) stained positive for the proteoglycan. By 5 days poststimulation, the percentage of network draining venules (18-59 microm) staining positive for NG2 returned to 18 +/- 7%, indicating a downregulation of the proteoglycan toward quiescent levels along larger-sized venules. CONCLUSIONS: The results suggest that NG2 proteoglycan expression is transiently upregulated along venules during microvascular remodeling, implicating NG2 as a marker of activated venules.