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Fulltext Ageing in Pgc-1β-/- mice modelling mitochondrial dysfunction induces differential expression of a range of genes regulating ventricular electrophysiology

Edling CE, Fazmin IT, Chadda KR, Ahmad S, Valli H, Grace AA, et al.

Biosci Rep, 2019 04 30;39(4).
PMID: 30914453 DOI: 10.1042/BSR20190127

Mice deficient in mitochondrial promoter peroxisome proliferator activated receptor-γ co-activator-1β (Pgc-1β-/- ) is a valuable model for metabolic diseases and has been found to present with several pathologies including ventricular arrhythmia. In the present study, our aim was to shed light on the molecular mechanisms behind the observed arrhythmic substrate by studying how the expression of selected genes critical for cardiac function differs in wild-type (WT) compared with Pgc-1β knockout mice and young compared with aged mice. We found that a clear majority of genes are down-regulated in the Pgc-1β-/- ventricular tissue compared with the WT. Although most individual genes are not significantly differentially expressed, a pattern is apparent when the genes are grouped according to their functional properties. Genes encoding proteins relating to ATPase activity, potassium ion channels relating to repolarisation and resting membrane potential, and genes encoding proteins in the cAMP pathway are found to be significantly down-regulated in the Pgc-1β deficient mice. On the contrary, the pacemaker channel genes Hcn3 and Hcn4 are up-regulated in subsets of the Pgc-1β deficient tissue. Furthermore, we found that with age, especially in the Pgc-1β-/- genotype, most genes are up-regulated including genes relating to the resting membrane potential, calcium homeostasis, the cAMP pathway, and most of the tested adrenoceptors. In conclusion, we here demonstrate how a complex pattern of many modest changes at gene level may explain major functional differences of the action potential related to ageing and mitochondrial dysfunction.

Matched MeSH terms: Heart Ventricles/physiopathology
Drawbacks in using hypercapnic acidosis in preoperative children with single ventricle physiology

Prakash ES

J Appl Physiol (1985), 2008 06;104(6):1841.
PMID: 18584792 DOI: 10.1152/japplphysiol.zdg-7979-pcpcomm.2008
Matched MeSH terms: Heart Ventricles/physiopathology
Fulltext Accelerometer-based atrioventricular synchronous pacing with a ventricular leadless pacemaker: Results from the Micra atrioventricular feasibility studies

Chinitz L, Ritter P, Khelae SK, Iacopino S, Garweg C, Grazia-Bongiorni M, et al.

Heart Rhythm, 2018 09;15(9):1363-1371.
PMID: 29758405 DOI: 10.1016/j.hrthm.2018.05.004

BACKGROUND: Micra is a leadless pacemaker that is implanted in the right ventricle and provides rate response via a 3-axis accelerometer (ACC). Custom software was developed to detect atrial contraction using the ACC enabling atrioventricular (AV) synchronous pacing.
OBJECTIVE: The purpose of this study was to sense atrial contractions from the Micra ACC signal and provide AV synchronous pacing.
METHODS: The Micra Accelerometer Sensor Sub-Study (MASS) and MASS2 early feasibility studies showed intracardiac accelerations related to atrial contraction can be measured via ACC in the Micra leadless pacemaker. The Micra Atrial TRacking Using A Ventricular AccELerometer (MARVEL) study was a prospective multicenter study designed to characterize the closed-loop performance of an AV synchronous algorithm downloaded into previously implanted Micra devices. Atrioventricular synchrony (AVS) was measured during 30 minutes of rest and during VVI pacing. AVS was defined as a P wave visible on surface ECG followed by a ventricular event <300 ms.
RESULTS: A total of 64 patients completed the MARVEL study procedure at 12 centers in 9 countries. Patients were implanted with a Micra for a median of 6.0 months (range 0-41.4). High-degree AV block was present in 33 patients, whereas 31 had predominantly intrinsic conduction during the study. Average AVS during AV algorithm pacing was 87.0% (95% confidence interval 81.8%-90.9%), 80.0% in high-degree block patients and 94.4% in patients with intrinsic conduction. AVS was significantly greater (P

Matched MeSH terms: Heart Ventricles/physiopathology*
Fulltext Ursodeoxycholic acid prevents ventricular conduction slowing and arrhythmia by restoring T-type calcium current in fetuses during cholestasis

Adeyemi O, Alvarez-Laviada A, Schultz F, Ibrahim E, Trauner M, Williamson C, et al.

PLoS One, 2017;12(9):e0183167.
PMID: 28934223 DOI: 10.1371/journal.pone.0183167

BACKGROUND: Increased maternal serum bile acid concentrations in intrahepatic cholestasis of pregnancy (ICP) are associated with fetal cardiac arrhythmias. Ursodeoxycholic acid (UDCA) has been shown to demonstrate anti-arrhythmic properties via preventing ICP-associated cardiac conduction slowing and development of reentrant arrhythmias, although the cellular mechanism is still being elucidated.
METHODS: High-resolution fluorescent optical mapping of electrical activity and electrocardiogram measurements were used to characterize effects of UDCA on one-day-old neonatal and adult female Langendorff-perfused rat hearts. ICP was modelled by perfusion of taurocholic acid (TC, 400μM). Whole-cell calcium currents were recorded from neonatal rat and human fetal cardiomyocytes.
RESULTS: TC significantly prolonged the PR interval by 11.0±3.5% (P<0.05) and slowed ventricular conduction velocity (CV) by 38.9±5.1% (P<0.05) exclusively in neonatal and not in maternal hearts. A similar CV decline was observed with the selective T-type calcium current (ICa,T) blocker mibefradil 1μM (23.0±6.2%, P<0.05), but not with the L-type calcium current (ICa,L) blocker nifedipine 1μM (6.9±6.6%, NS). The sodium channel blocker lidocaine (30μM) reduced CV by 60.4±4.5% (P<0.05). UDCA co-treatment was protective against CV slowing induced by TC and mibefradil, but not against lidocaine. UDCA prevented the TC-induced reduction in the ICa,T density in both isolated human fetal (-10.2±1.5 versus -5.5±0.9 pA/pF, P<0.05) and neonatal rat ventricular myocytes (-22.3±1.1 versus -9.6±0.8 pA/pF, P<0.0001), whereas UDCA had limited efficacy on the ICa,L.
CONCLUSION: Our findings demonstrate that ICa,T plays a significant role in ICP-associated fetal cardiac conduction slowing and arrhythmogenesis, and is an important component of the fetus-specific anti-arrhythmic activity of UDCA.

Matched MeSH terms: Heart Ventricles/physiopathology*
Fulltext The RyR2-P2328S mutation downregulates Nav1.5 producing arrhythmic substrate in murine ventricles

Ning F, Luo L, Ahmad S, Valli H, Jeevaratnam K, Wang T, et al.

Pflugers Arch, 2016 Apr;468(4):655-65.
PMID: 26545784 DOI: 10.1007/s00424-015-1750-0

Catecholaminergic polymorphic ventricular tachycardia (CPVT) predisposes to ventricular arrhythmia due to altered Ca(2+) homeostasis and can arise from ryanodine receptor (RyR2) mutations including RyR2-P2328S. Previous reports established that homozygotic murine RyR2-P2328S (RyR2 (S/S)) hearts show an atrial arrhythmic phenotype associated with reduced action potential (AP) conduction velocity and sodium channel (Nav1.5) expression. We now relate ventricular arrhythmogenicity and slowed AP conduction in RyR2 (S/S) hearts to connexin-43 (Cx43) and Nav1.5 expression and Na(+) current (I Na). Stimulation protocols applying extrasystolic S2 stimulation following 8 Hz S1 pacing at progressively decremented S1S2 intervals confirmed an arrhythmic tendency despite unchanged ventricular effective refractory periods (VERPs) in Langendorff-perfused RyR2 (S/S) hearts. Dynamic pacing imposing S1 stimuli then demonstrated that progressive reductions of basic cycle lengths (BCLs) produced greater reductions in conduction velocity at equivalent BCLs and diastolic intervals in RyR2 (S/S) than WT, but comparable changes in AP durations (APD90) and their alternans. Western blot analyses demonstrated that Cx43 protein expression in whole ventricles was similar, but Nav1.5 expression in both whole tissue and membrane fractions were significantly reduced in RyR2 (S/S) compared to wild-type (WT). Loose patch-clamp studies similarly demonstrated reduced I Na in RyR2 (S/S) ventricles. We thus attribute arrhythmogenesis in RyR2 (S/S) ventricles resulting from arrhythmic substrate produced by reduced conduction velocity to downregulated Nav1.5 reducing I Na, despite normal determinants of repolarization and passive conduction. The measured changes were quantitatively compatible with earlier predictions of linear relationships between conduction velocity and the peak I Na of the AP but nonlinear relationships between peak I Na and maximum Na(+) permeability.

Matched MeSH terms: Heart Ventricles/physiopathology
Fulltext Concomitant stenting of the patent ductus arteriosus and radiofrequency valvotomy in pulmonary atresia with intact ventricular septum and intermediate right ventricle: early in-hospital and medium-term outcomes

Alwi M, Choo KK, Radzi NA, Samion H, Pau KK, Hew CC

J. Thorac. Cardiovasc. Surg., 2011 Jun;141(6):1355-61.
PMID: 21227471 DOI: 10.1016/j.jtcvs.2010.08.085

Objectives: Our objective was to determine the feasibility and early to medium-term outcome of stenting the patent ductus arteriosus at the time of radiofrequency valvotomy in the subgroup of patients with pulmonary atresia with intact ventricular septum and intermediate right ventricle.
Background: Stenting of the patent ductus arteriosus and radiofrequency valvotomy have been proposed as the initial intervention for patients with intermediate right ventricle inasmuch as the sustainability for biventricular circulation or 1½-ventricle repair is unclear in the early period.
Methods: Between January 2001 and April 2009, of 143 patients with pulmonary atresia and intact ventricular septum, 37 who had bipartite right ventricle underwent radiofrequency valvotomy and stenting of the patent ductus arteriosus as the initial procedure. The mean tricuspid valve z-score was -3.8 ± 2.2 and the mean tricuspid valve/mitral valve ratio was 0.62 ± 0.16.
Results: Median age was 10 days (3-65 days) and median weight 3.1 kg (2.4-4.9 kg). There was no procedural mortality. Acute stent thrombosis developed in 1 patient and necessitated emergency systemic-pulmonary shunt. There were 2 early in-hospital deaths owing to low cardiac output syndrome. One late death occurred owing to right ventricular failure after the operation. Survival after the initial procedure was 94% at 6 months and 91% at 5 years. At a median follow-up of 4 years (6 months to 8 years), 17 (48%) attained biventricular circulation with or without other interventions and 9 (26%) achieved 1½-ventricle repair. The freedom from reintervention was 80%, 68%, 58%, and 40% at 1, 2, 3, and 4 years, respectively.
Conclusions: Concomitant stenting of the patent ductus arteriosus at the time of radiofrequency valvotomy in patients with pulmonary atresia with intact ventricular septum and intermediate right ventricle is feasible and safe with encouraging medium-term outcome.

Matched MeSH terms: Heart Ventricles/physiopathology