A 50% Reduction of Excitability but Not of Intercellular Coupling Affects Conduction Velocity Restitution and Activation Delay in the Mouse Heart

Computer simulations suggest that intercellular coupling is more robust than membrane excitability with regard to changes in and safety of conduction. Clinical studies indicate that SCN5A (excitability) and/or Connexin43 (Cx43, intercellular coupling) expression in heart disease is reduced by approximately 50%. In this retrospective study we assessed the effect of reduced membrane excitability or intercellular coupling on conduction in mouse models of reduced excitability or intercellular coupling. Epicardial activation mapping of LV and RV was performed on Langendorff-perfused mouse hearts having the following: 1) Reduced excitability: Scn5a haploinsufficient mice; and 2) reduced intercellular coupling: Cx43(CreER(T)/fl) mice, uninduced (50% Cx43) or induced (10% Cx43) with Tamoxifen. Wild type (WT) littermates were used as control. Conduction velocity (CV) restitution and activation delay were determined longitudinal and transversal to fiber direction during S(1)S(1) pacing and S(1)S(2) premature stimulation until the effective refractory period. In both animal models, CV restitution and activation delay in LV were not changed compared to WT. In contrast, CV restitution decreased and activation delay increased in RV during conduction longitudinal but not transverse to fiber direction in Scn5a heterozygous animals compared to WT. In contrast, a 50% reduction of intercellular coupling did not affect either CV restitution or activation delay. A decrease of 90% Cx43, however, resulted in decreased CV restitution and increased activation delay in RV, but not LV. Reducing excitability but not intercellular coupling by 50% affects CV restitution and activation delay in RV, indicating a higher safety factor for intercellular coupling than excitability in R

Clinical outcomes of complex real-world diabetic patients treated with amphilimus sirolimus-eluting stents or zotarolimus-eluting stents : A single-center registry

Objective: To assess clinical outcomes of Amphilimus Sirolimus-Eluting Stents (A-SES) as compared to Zotarolimus-Eluting Stents (ZES) in complex real-world diabetic patients. Background: Patients with diabetes mellitus represent one of the most challenging scenarios with high rates of restenosis and stent thrombosis in the current era of drug-eluting stents. Hence, we assessed the safety of A-SES versus ZES in complex diabetic patients. Methods: In this observational study, we analyzed all consecutive patients with diabetes mellitus referred to our center from November 2012 to November 2014. The primary outcome was target-lesion failure at 1-year follow-up. Results: A total of 165 consecutive diabetic patients underwent percutaneous coronary intervention with A-SES or ZES for stable coronary artery disease in our tertiary center. Using the Kaplan Meier method the cumulative incidence of target-lesion failure was 6.7% (5.9% A-SES versus 7.5% ZES, p = 0.19) at 1-year follow-up. Event-free survival at 1. year follow-up was similar (89.4% A-SES vs. 83.3% ZES, p = 0.29). Interestingly, we did not find any cases of definite-, and only one case of probable stent thrombosis in this high risk cohort. Conclusion: In this real-world registry, A-SES and ZES seems to be associated with promising 1-year clinical safety outcomes following PCI in a contemporary cohort of high-risk diabetic patients. Our results should be considered hypothesis generating, as the clinical safety of A-SES has to be confirmed in a large trial

Determination of Conduction Velocity and Activation delay.

<p><b>A.</b> The ventricles were stimulated from the center of the grid at S₁S₁ stimulation of 100 ms. The stimulation protocol was composed of sixteen basic stimuli followed by 1 premature stimulus (S₁S₂). The premature stimulus started at 90 ms and at the subsequent trains, the coupling interval of the premature stimulus was reduced in steps of 5 ms, until the effective refractory period (ERP) was reached, which was defined as the longest possible coupling interval of the premature stimulus that fails to activate the entire heart. <b>B.</b> CV parallel (longitudinal; CV_L) and perpendicular (transverse; CV_T) to myocyte fiber direction was determined from each activation map. For CVL, the distance between 4 consecutive electrodes parallel to fiber orientation and perpendicular to the isochrones was measured (x) and divided by the time difference (6−2 = 4 ms). Similarly, CVT was determined as Δy/Δt. Activation delay is defined as the local activation time (stimulus is time zero) at a fixed distance from the center of activation origin (stimulus site). Activation delay is registered at two sites (A and B), located on a line parallel to longitudinal and transversal conduction propagation during S₁S₁. Subsequently, activation delay is measured at the same sites during the premature stimuli S₁S₂. Finally, activation delay is normalized by substracting the activation delays of S₁S₁ from activation delay at S₁S₂.</p

Activation maps of wild-type and <i>Scn5a</i> heterozygous RV.

<p>RV activation maps of WT (panel A) and <i>Scn5a</i> heterozygous (panel B) mice paced at S₁S₁ of 100 ms and during S₁S₂ activation with 5 ms decrement until the effective refractory period is reached. Isochronal lines are set to 1 ms. Red denotes earliest activation, blue latest. Equal color represents equal activation times.</p

Summary of right and left ventricular CV restitution and activation delay.

<p>k = increased; l = decreased; ∼ = unchanged.</p

Reduced membrane excitability group conduction velocity and stimulus-to-activation delay measurements.

<p>All values are mean±SEM. WT – wild-type, HZ – heterozygous. S₁S₂ coupling interval is in ms. CV_L/_T – longitudinal/transverse conduction velocity (cm/s); StAD_L/_T – stimulus-to-activation delay longitudinal/transverse (ms).</p>*<p>intra-variable differences: P<0.05 between consecutive S₁S₂ and S₁S₂-5 ms.</p><p>Inter-variable differences are within either RV or LV:</p>§<p>P<0.05 between wild-type and heterozygous animals.</p

Reduced intercellular coupling group conduction velocity and stimulus-to-activation delay measurements.

<p>All values are mean±SEM. S1S2 coupling interval is in ms. CVL/T – longitudinal/transverse conduction velocity (cm/s); StADL/T – stimulus-to-activation delay longitudinal/transverse (ms).</p><p>*intra-variable differences: P<0.05 between consecutive S1S2 and S1S2-5 ms.</p><p>Inter-variable differences are within either RV or LV:</p>§<p>P<0.05 between 100% and 50% Cx43.</p>†<p>P<0.05 between ventricles with 50% and 10% Cx43.</p>¥<p>P<0.05 between ventricles with 100% and 10% Cx43.</p

CV restitution and activation delay curves of mice demonstrating reduced membrane excitability.

<p>CV restitution (solid markers) and activation delay (open markers) curves of WT (circles) and <i>Scn5a</i> HZ (squares). Hearts are paced at S₁S₁ of 100 ms with S₁S₂ coupling interval reduced in steps of 5 ms until the effective refractory period. A and B demonstrate the RV and LV CV_L restitution and activation delay curves, C and D show the curves during transverse propagation.</p

Spatial Heterogeneity of Cx43 is an Arrhythmogenic Substrate of Polymorphic Ventricular Tachycardias during Compensated Cardiac Hypertrophy in Rats

BACKGROUND: Ventricular remodeling increases the propensity of ventricular tachyarrhythmias and sudden death in patients. We studied the mechanism underlying these fatal arrhythmias, electrical and structural cardiac remodeling, as well as arrhythmogeneity during early, compensated hypertrophy in a rat model of chronic pressure overload. METHODS: Twenty-six Wistar rats were subjected to transverse aortic constriction (TAC) (n = 13) or sham operation (n = 13). Four weeks postoperative, echo- and electrocardiography was performed. Epicardial (208 or 455 sites) and transmural (30 sites) ventricular activation mapping was performed on Langendorff perfused hearts. Subsequently, hearts were processed for (immuno)histological and molecular analyses. RESULTS: TAC rats showed significant hypertrophy with preserved left ventricular (LV) function. Epicardial conduction velocity (CV) was similar, but more dispersed in TAC. Transmural CV was slowed in TAC (37.6 ± 2.9 cm s(-1)) compared to sham (58.5 ± 3.9 cm s(-1); P < 0.01). Sustained polymorphic ventricular tachycardias were induced from LV in 8/13 TAC and in 0/13 sham rats. During VT, electrical activation patterns showed variable sites of earliest epicardial activation and altering sites of functional conduction block. Wandering epicardial reentrant activation was sporadically observed. Collagen deposition was significantly higher in TAC compared to sham, but not different between arrhythmogenic and non-arrhythmogenic TAC animals. Connexin43 (Cx43) expression was heterogeneous with a higher prevalence of non-phosphorylated Cx43 in arrhythmogenic TAC animals. CONCLUSION: In TAC rats with compensated cardiac hypertrophy, dispersion of conduction correlated to arrhythmogenesis, an increased heterogeneity of Cx43, and a partial substitution with non-phosphorylated Cx43. These alterations may result in the increased vulnerability to polymorphic VTs

Combined reduction of intercellular coupling and membrane excitability differentially affects transverse and longitudinal cardiac conduction

Aims Reduced excitability and gap junction expression are commonly found in electrically remodelled diseased hearts, but their contribution to slow conduction and arrhythmias is unclear. In this study, we have investigated the effect of isolated and combined reductions in membrane excitability and intercellular coupling on impulse propagation and arrhythmogeneity in genetically modified mice. Methods and results Cx43 and Scn5a(1798insD/+) heterozygous (HZ) mice were crossbred to create a mixed offspring: wild-type (WT, n = 15), Cx43 HZ (n = 14), Scn5a(1798insD/+) (Scn5a) HZ (n = 17), and Cx43/Scn5a(1798insD/+) (Cx43/Scn5a) HZ (n = 15) mice. After ECG recording, epicardial activation mapping (208 recording sites) was performed on Langendorff-perfused hearts. Arrhythmia inducibility was tested by one to three premature stimuli and burst pacing. Conduction velocity longitudinal (CVL) and transverse (CVT) to fibre orientation and dispersion of conduction were determined during S1-S1 pacing (150 ms). Connexin43 (Cx43) and sodium channel Nav1.5 protein expression and myocardial tissue collagen content were determined by immunohistology. Compared with WT animals, P, QRS, and QTc intervals were prolonged in Scn5a HZ and Cx43/Scn5a HZ, but not in Cx43 HZ animals. Scn5a HZ mice showed decreased CVL in right ventricle (RV) but not in left ventricle compared with WT. In the RV of Cx43/Scn5a HZ, CVT was reduced, but CVL was not different from WT. Arrhythmia inducibility was low and not increased in either single- or double-mutant mice. Conclusion Reduction of both electrical coupling and excitability results in normal conduction velocity parallel to fibre orientation but in pronounced conduction slowing transverse to fibre orientation in RV only, although this does not affect arrhythmogeneit