Myofibroblasts impair myocardial impulse propagation by heterocellular connexin43 gap-junctional coupling through micropores.

Aim: Composite population of myofibroblasts (MFs) within myocardial tissue is known to alter impulse propagation, leading to arrhythmias. However, it remains unclear whether and how MFs alter their propagation patterns when contacting cardiomyocytes (CMs) without complex structural insertions in the myocardium. We attempted to unveil the effects of the one-sided, heterocellular CM-MF connection on the impulse propagation of CM monolayers without the spatial insertion of MFs as an electrical or mechanical obstacle. Methods and results: We evaluated fluo8-based spatiotemporal patterns in impulse propagation of neonatal rat CM monolayers cultured on the microporous membrane having 8-µm diameter pores with co-culture of MFs or CMs on the reverse membrane side (CM-MF model or CM-CM model, respectively). During consecutive pacing at 1 or 2 Hz, the CM monolayers exhibited forward impulse propagation from the pacing site with a slower conduction velocity (θ) and a larger coefficient of directional θ variation in the CM-MF model than that in the CM-CM model in a frequency-dependent manner (2 Hz >1 Hz). The localized placement of an MF cluster on the reverse side resulted in an abrupt segmental depression of the impulse propagation of the upper CM layer, causing a spatiotemporally non-uniform pattern. Dye transfer of the calcein loaded in the upper CM layer to the lower MF layer was attenuated by the gap-junction inhibitor heptanol. Immunocytochemistry identified definitive connexin 43 (Cx43) between the CMs and MFs in the membrane pores. MF-selective Cx43 knockdown in the MF layer improved both the velocity and uniformity of propagation in the CM monolayer. Conclusion: Heterocellular Cx43 gap junction coupling of CMs with MFs alters the spatiotemporal patterns of myocardial impulse propagation, even in the absence of spatially interjacent and mechanosensitive modulations by MFs. Moreover, MFs can promote pro-arrhythmogenic impulse propagation when in face-to-face contact with the myocardium that arises in the healing infarct border zone.

Generation of myocyte agonal Ca2+ waves and contraction bands in perfused rat hearts following irreversible membrane permeabilisation.

Although irreversible cardiomyocyte injury provokes intracellular Ca2+ ([Ca2+]i) overload, the underlying dynamics of this response and its effects on cellular morphology remain unknown. We therefore visualised rapid-scanning confocal fluo4-[Ca2+]i dynamics and morphology of cardiomyocytes in Langendorff-perfused rat hearts following saponin-membrane permeabilisation. Our data demonstrate that 0.4% saponin-treated myocytes immediately exhibited high-frequency Ca2+ waves (131.3 waves/min/cell) with asynchronous, oscillatory contractions having a mean propagation velocity of 117.8 µm/s. These waves slowly decreased in frequency, developed a prolonged decay phase, and disappeared in 10 min resulting in high-static, fluo4-fluorescence intensity. The myocytes showing these waves displayed contraction bands, i.e., band-like actin-fibre aggregates with disruption of sarcomeric α-actinin. The contraction bands were not attenuated by the abolition of Ca2+ waves under pretreatment with ryanodine plus thapsigargin, but were partially attenuated by the calpain inhibitor MDL28170, while mechanical arrest of the myocytes by 2,3-butanedione monoxime completely attenuated contraction-band formation. The depletion of adenosine 5'-triphosphate by the mitochondrial electron uncoupler carbonyl cyanide 4-trifluoromethoxy phenylhydrazone also attenuated Ca2+ waves and contraction bands. Overall, saponin-induced myocyte [Ca2+]i overload provokes agonal Ca2+ waves and contraction bands. Contraction bands are not the direct consequence of the waves but are caused by cross-bridge interactions of the myocytes under calpain-mediated proteolysis.

Efficacy of bubble contrast echocardiography in detecting pulmonary arteriovenous fistulas in children with univentricular heart after total cavopulmonary connection.

BACKGROUND: Development of pulmonary arteriovenous fistulas in patients with cavopulmonary anastomosis may result in a significant morbidity. Although the use of bubble contrast echocardiography with selective injection into both the branch pulmonary arteries in identifying pulmonary arteriovenous fistulas has been increasing, the actual efficacy of this diagnostic modality has not been properly evaluated. Thus, this study aimed to assess the efficacy of bubble contrast echocardiography in detecting pulmonary arteriovenous fistulas in children with total cavopulmonary connection. METHODS: A total of 140 patients were included. All patients underwent cardiac catheterisation. Bubble contrast echocardiographic studies were performed by injecting agitated saline solution into the branch pulmonary arteries. Transthoracic echocardiograms that use an apical view were conducted to assess the appearance of bubble contrast in the systemic ventricles. Then, the contrast echocardiogram results and other cardiac parameters were compared. RESULTS: No correlation was found between contrast echocardiogram grade and other cardiac parameters, such as pulmonary capillary wedge saturation and pulmonary artery resistance. Moreover, only 13 patients had negative results on both the right and left contrast echocardiograms, and 127 of the 140 patients had positive results on contrast echocardiograms even though they had normal pulmonary capillary wedge saturation. Results showed that bubble contrast echocardiography was a highly sensitive method and was likely to obtain false-positive results. CONCLUSIONS: Bubble contrast echocardiography might be highly false positive in detecting pulmonary arteriovenous fistulas in patients with cavopulmonary anastomosis. We have to consider how we make use of this method. Further standardisation of techniques is required.

Kidney injury biomarkers after cardiac angiography in children with congenital heart disease.

OBJECTIVE: This study aims to investigate the changes in renal function and levels of urinary biomarkers before and after cardiac angiography in children with congenital heart disease (CHD). SETTING: Children with CHD are at a risk for kidney injury during contrast exposure in cardiac angiography. OUTCOME MEASURES: We measured urinary protein, albumin, N-acetyl-ß-D-glucosaminidase (NAG), ß2-microglobulin (BMG), and liver-type fatty acid-binding protein (L-FABP) levels, as well as serum creatinine and cystatin C levels, before and after cardiac angiography in 33 children with CHD. RESULTS: No significant decrease was noted in either the creatinine-based or cystatin C-based estimated glomerular filtration rate at 24 hours after angiography compared with that before angiography. Urinary protein, NAG, BMG, and L-FABP levels were significantly increased at 24 hours after angiography, all of which returned to baseline levels at more than 7 days after angiography. An increase in urinary level of protein, albumin, NAG, or BMG was mostly associated with increased urinary L-FABP level. An increase in both urinary BMG and L-FABP, but not that in urinary L-FABP alone, was associated with increased levels of urinary protein and NAG, as well as the greater dose of contrast media. CONCLUSIONS: Transient increases of kidney injury biomarkers following cardiac angiography are not necessarily associated with the impairment of renal function in a short time period; however, the increase in urinary protein, albumin, NAG, or BMG level may indicate greater stresses to the kidneys than the increase in urinary L-FABP alone in children with CHD.