Delphine Mika

This article proposes a new integrated analog implementation of the Pan–Tompkins algorithm. This algorithm, generally implemented in the digital domain at the cost of higher power consumption, is one of the most efficient for QRS detection in electrocardiographic signals. This circuit has been designed for use on small mammals like rats for the study of pulmonary arterial hypertension. The specificities of the architecture proposed in this article are a sub-threshold-operated architecture to perform the amplification, noise filtering, and differentiation of the signal in a unique block to limit the power consumption; an analog squarer; and an analog monostable reshaping-circuit followed by a digital counter clocked by an ultra-low power relaxation oscillator. Compared with the state of the art, this circuit, designed with the X-FAB xh018 180 nm CMOS technology, presents one of the lowest power consumptions currently reported, at 28.5 nW, 76% of which is consumed in the current, voltage, and time references. Post-layout simulation results show a reliable 98.57% heart beat detection accuracy using the MIT-BIH arrhythmia database and 99.85% accuracy for healthy sinus rhythm electrocardiograms. The robustness of the circuit is also investigated, and mitigating solutions are proposed for each critical block.

Aims: The cAMP-specific phosphodiesterases 4B and 4D (PDE4B and PDE4D) are critical regulators of cardiac excitation-contraction coupling, but their role in controlling heart rate (HR) remains poorly defined. This study aimed to evaluate their respective contributions to cardiac automaticity. Methods and results: PDE4 activity, measured by a radioenzymatic assay, accounted for ∼60% of the total cAMP-hydrolytic activity in the mouse sinoatrial node (SAN). Western blot and in situ RNA fluorescence hybridization (RNAscopeTM) showed that both PDE4B and PDE4D are expressed in the SAN and in isolated pacemaker cardiomyocytes. HR, measured by electrocardiogram (ECG) telemetry, was increased in Pde4b knockout (Pde4b−/−) and Pde4d knockout (Pde4d−/−) mice compared with wild-type (WT) littermates, during both day and night. Upon autonomic nervous system blockade, elevated HR persisted in Pde4b−/− but not in Pde4d−/− mice. Consistently, isolated perfused hearts from Pde4b−/− mice beat faster than WT littermates, whereas Pde4d−/− did not. Increased automaticity in Pde4b−/− hearts was not accompanied by modified Ca2+ homeostasis in Fluo-4-loaded isolated SAN tissue, either at baseline or during β-adrenergic (β-AR) stimulation with 10 nM isoprenaline (ISO). In contrast, Pde4d−/− SAN challenged with ISO exhibited an increased total sarcoplasmic reticulum Ca2+ leak and prolonged Ca2+ transients. Patch-clamp recordings revealed an increased action potential firing rate in Pde4b−/− but not in Pde4d−/− pacemaker cardiomyocytes. In Pde4b−/− cells, basal and ISO-stimulated L-type calcium current (ICa,L) densities were not significantly altered, whereas funny current (If) density was increased. Conversely, Pde4d ablation did not alter basal ICa,L nor If. Conclusion: These results show that PDE4B controls intrinsic SAN automaticity by regulating the voltage clock through the pacemaker current If, whereas PDE4D regulates the calcium clock via β-AR-induced calcium release through RyR2.

Background: PDE2 (phosphodiesterase 2) is upregulated in human heart failure. Cardiac PDE2‐transgenic mice are protected against contractile dysfunction and arrhythmias in heart failure but whether an acute elevation of PDE2 could be of therapeutic value remains elusive. This hypothesis was tested using cardiac PDE2 gene transfer in preclinical models of heart failure. Methods and Results: C57BL/6 male mice were injected with serotype 9 adeno‐associated viruses encoding for PDE2A. This led to a ≈10‐fold rise of PDE2A protein levels that affected neither cardiac structure nor function in healthy mice. Two weeks after inoculation with serotype 9 adeno‐associated viruses, mice were implanted with minipumps delivering either NaCl, isoproterenol (60 mg/kg per day), or isoproterenol and phenylephrine (30 mg/kg per day each) for 2 weeks. In mice injected with serotype 9 adeno‐associated viruses encoding for LUC (luciferase), isoproterenol or isoproterenol+phenylephrine infusion induced left ventricular hypertrophy, decreased ejection fraction unveiled by echocardiography, and promoted fibrosis and apoptosis assessed by Masson's trichrome and Tunel, respectively. Furthermore, inotropic responses to isoproterenol of ventricular cardiomyocytes isolated from isoproterenol+phenylephrine‐LUC mice loaded with 1 μmol/L Fura‐2AM and stimulated at 1 Hz to record calcium transients and sarcomere shortening were dampened. Spontaneous calcium waves at the cellular level were promoted as well as ventricular arrhythmias evoked in vivo by catheter‐mediated ventricular pacing after isoproterenol (1.5 mg/kg) and atropine (1 mg/kg) injection. However, increased PDE2A blunted these adverse outcomes evoked by sympathomimetic amines. Conclusions: Cardiac gene therapy with PDE2A limits left ventricle remodeling, dysfunction, and arrhythmias evoked by catecholamines, providing evidence that increasing PDE2A activity acutely could prevent progression toward heart failure.

BACKGROUND: The heart expresses 2 main subtypes of cAMP-dependent protein kinase (PKA; type I and II) that differ in their regulatory subunits, RIα and RIIα. Embryonic lethality of RIα knockout mice limits the current understanding of type I PKA function in the myocardium. The objective of this study was to test the role of RIα in adult heart contractility and pathological remodeling. METHODS: We measured PKA subunit expression in human heart and developed a conditional mouse model with cardiomyocyte-specific knockout of RIα (RIα-icKO). Myocardial structure and function were evaluated by echocardiography, histology, and ECG and in Langendorff-perfused hearts. PKA activity and cAMP levels were determined by immunoassay, and phosphorylation of PKA targets was assessed by Western blot. L-type Ca ²⁺ current ( I _Ca,L ), sarcomere shortening, Ca ²⁺ transients, Ca ²⁺ sparks and waves, and subcellular cAMP were recorded in isolated ventricular myocytes (VMs). RESULTS: RIα protein was decreased by 50% in failing human heart with ischemic cardiomyopathy and by 75% in the ventricles and in VMs from RIα-icKO mice but not in atria or sinoatrial node. Basal PKA activity was increased ≈3-fold in RIα-icKO VMs. In young RIα-icKO mice, left ventricular ejection fraction was increased and the negative inotropic effect of propranolol was prevented, whereas heart rate and the negative chronotropic effect of propranolol were not modified. Phosphorylation of phospholamban, ryanodine receptor, troponin I, and cardiac myosin-binding protein C at PKA sites was increased in propranolol-treated RIα-icKO mice. Hearts from RIα-icKO mice were hypercontractile, associated with increased I _Ca,L, and [Ca ²⁺ ] _i transients and sarcomere shortening in VMs. These effects were suppressed by the PKA inhibitor, H89. Global cAMP content was decreased in RIα-icKO hearts, whereas local cAMP at the phospholamban/sarcoplasmic reticulum Ca ²⁺ ATPase complex was unchanged in RIα-icKO VMs. RIα-icKO VMs had an increased frequency of Ca ²⁺ sparks and proarrhythmic Ca ²⁺ waves, and RIα-icKO mice had an increased susceptibility to ventricular tachycardia. On aging, RIα-icKO mice showed progressive contractile dysfunction, cardiac hypertrophy, and fibrosis, culminating in congestive heart failure with reduced ejection fraction that caused 50% mortality at 1 year. CONCLUSIONS: These results identify RIα as a key negative regulator of cardiac contractile function, arrhythmia, and pathological remodeling.

β-Adrenergic receptors (β-ARs) enhance cardiac contractility by increasing cAMP levels and activating PKA. PKA increases Ca²⁺-induced Ca²⁺ release via phosphorylation of L-type Ca²⁺ channels (LTCCs) and ryanodine receptor 2. Multiple cyclic nucleotide phosphodiesterases (PDEs) regulate local cAMP concentration in cardiomyocytes, with PDE4 being predominant for the control of β-AR–dependent cAMP signals. Three genes encoding PDE4 are expressed in mouse heart: Pde4a, Pde4b, and Pde4d. Here we show that both PDE4B and PDE4D are tethered to the LTCC in the mouse heart but that β-AR stimulation of the L-type Ca²⁺ current (I_Ca,L) is increased only in Pde4b^–/– mice. A fraction of PDE4B colocalized with the LTCC along T-tubules in the mouse heart. Under β-AR stimulation, Ca²⁺ transients, cell contraction, and spontaneous Ca²⁺ release events were increased in Pde4b^–/– and Pde4d^–/– myocytes compared with those in WT myocytes. In vivo, after intraperitoneal injection of isoprenaline, catheter-mediated burst pacing triggered ventricular tachycardia in Pde4b^–/– mice but not in WT mice. These results identify PDE4B in the Ca_V1.2 complex as a critical regulator of I_Ca,L during β-AR stimulation and suggest that distinct PDE4 subtypes are important for normal regulation of Ca²⁺-induced Ca²⁺ release in cardiomyocytes.