Exclusion of alternative exon 33 of CaV1.2 calcium channels in heart is proarrhythmogenic.

Alternative splicing changes the CaV1.2 calcium channel electrophysiological property, but the in vivo significance of such altered channel function is lacking. Structure-function studies of heterologously expressed CaV1.2 channels could not recapitulate channel function in the native milieu of the cardiomyocyte. To address this gap in knowledge, we investigated the role of alternative exon 33 of the CaV1.2 calcium channel in heart function. Exclusion of exon 33 in CaV1.2 channels has been reported to shift the activation potential -10.4 mV to the hyperpolarized direction, and increased expression of CaV1.2Δ33 channels was observed in rat myocardial infarcted hearts. However, how a change in CaV1.2 channel electrophysiological property, due to alternative splicing, might affect cardiac function in vivo is unknown. To address these questions, we generated mCacna1c exon 33-/--null mice. These mice contained CaV1.2Δ33 channels with a gain-of-function that included conduction of larger currents that reflects a shift in voltage dependence and a modest increase in single-channel open probability. This altered channel property underscored the development of ventricular arrhythmia, which is reflected in significantly more deaths of exon 33-/- mice from ß-adrenergic stimulation. In vivo telemetric recordings also confirmed increased frequencies in premature ventricular contractions, tachycardia, and lengthened QT interval. Taken together, the significant decrease or absence of exon 33-containing CaV1.2 channels is potentially proarrhythmic in the heart. Of clinical relevance, human ischemic and dilated cardiomyopathy hearts showed increased inclusion of exon 33. However, the possible role that inclusion of exon 33 in CaV1.2 channels may play in the pathogenesis of human heart failure remains unclear.

Assessment of left atrial appendage function by transthoracic pulsed Doppler echocardiography: Comparing against transesophageal interrogation and predicting echocardiographic risk factors for stroke.

AIMS: Transesophageal echocardiographic (TEE) findings of left atrial appendage (LAA) thrombus, spontaneous echo contrast (SEC), and LAA dysfunction are established risk factors of cardioembolic stroke. The semi-invasive nature of TEE limits its utility as a routine risk stratification tool. We aim to correlate TEE and transthoracic echocardiography (TTE) pulsed Doppler measurements of LAA flow velocities and use TTE measurements to predict TEE findings. METHODS AND RESULTS: We prospectively measured pulsed Doppler LAA flow velocities in 103 consecutive patients on TEE and TTE. There was a strong correlation between TEE and TTE LAA emptying velocity (LAA E) (r = .88, P < .001) and a moderate correlation between LAA filling velocities (r = .50, P < .001). TTE LAA E predicted the presence of thrombus or SEC independent of atrial fibrillation (AF). To predict the presence of thrombus or SEC, the optimal TTE LAA E cutoff was ≤30 cm/s in all patients (75% sensitive, 90% specific) and ≤31 cm/s in AF patients (80% sensitive, 79% specific). To predict LAA dysfunction (TEE E ≤ 20 cm/s), the optimal TTE LAA E cutoff was ≤27 cm/s (100% sensitive, 89% specific in all patients and 100% sensitive, 74% specific in AF patients). CONCLUSIONS: TTE assessment of LAA function is feasible and correlates well with the more invasive TEE method. It predicts the presence of thrombus, SEC, and LAA dysfunction on TEE. TTE LAA assessment has incremental value in thromboembolic risk stratification and should be utilized more frequently.

Clinical characteristics, treatment and long-term outcomes of patients with right-sided cardiac thrombus.

OBJECTIVE: Right-sided cardiac thrombus is rare and may be caused by venous thromboembolism, in association with medical devices or stasis of blood in atrial fibrillation (AF) and cardiomyopathies. Complications include pulmonary embolism (PE) and paradoxical stroke. Current data are limited and mostly from case series and PE registries. We aimed to describe the clinical characteristics, echocardiographic features, treatments, and outcomes of right-sided cardiac thrombus patients. METHODS: This was a retrospective observational study of 97 consecutive patients with right-sided cardiac thrombus detected on echocardiography. We studied co-morbidities, predisposing factors, thrombus characteristics, and therapeutic interventions and assessed their associations with the development of PE, paradoxical stroke, circulatory collapse, and all-cause mortality. RESULTS: The mean age was 58.7 years, and 55/97 (56.7%) of the participants were female. Ischemic heart disease (IHD), heart failure, chronic kidney disease, and malignancy were common co-morbidities. Right atrial (RA) thrombus was often associated with medical devices, while right ventricular (RV) thrombus was more commonly associated with cardiomyopathy. Thrombus mobility did not affect embolic events but was associated with greater short-term mortality. On multivariable analysis, anticoagulation (HR 0.25, 95% CI 0.09-0.68) and thrombus resolution (HR 0.28, 95% CI 0.13-0.62) were associated with greater survival. CONCLUSION: Right-sided cardiac thrombus is rare but may have potentially life-threatening complications such as PE and paradoxical stroke. Further research is needed to determine the optimal therapeutic strategies for this poorly studied population.

Transplantation of Endothelial Progenitor Cells in Obese Diabetic Rats Following Myocardial Infarction: Role of Thymosin Beta-4.

Endothelial progenitor cells (EPCs) are bone-marrow derived cells that are critical in the maintenance of endothelial wall integrity and protection of ischemic myocardium through the formation of new blood vessels (vasculogenesis) or proliferation of pre-existing vasculature (angiogenesis). Diabetes mellitus (DM) and the metabolic syndrome are commonly associated with ischemic heart disease through its pathological effects on the endothelium and consequent endothelial dysfunction. Thymosin-ß4 (Tß4) which expressed in the embryonic heart is critical in epicardial and coronary artery formation. In this study, we explored the effects of Tß4 treatment on diabetic EPCs in vitro and intramyocardial injection of Tß4-treated and non-Tß4 treated EPCs following acute myocardial infarction (MI) of diabetic rats in vivo. It was found that 10 ng/mL Tß4 increased migration, tubule formation, and angiogenic factor secretion of diabetic EPCs in vitro. In vivo, although implantation of Tß4 treated diabetic EPCs significantly increased capillary density and attracted more c-Kit positive progenitor cells into the infarcted hearts as compared with implantation of non-Tß4 treated diabetic EPCs, the significantly improved left ventricular ejection fraction was only found in the rats which received non-Tß4 treated EPCs. The data suggests that a low dose Tß4 increases diabetic EPC migration, tubule formation, and angiogenic factor secretion. However, it did not improve the effects of EPCs on left ventricular pump function in diabetic rats with MI.