Right ventricular failure secondary to chronic overload in congenital heart disease: an experimental model for therapeutic innovation.

OBJECTIVE: Mortality and morbidity related to right ventricular failure remain a problem for the long-term outcome of congenital heart diseases. Therapeutic innovation requires establishing an animal model reproducing right ventricular dysfunction secondary to chronic pressure-volume overload. METHODS: Right ventricular tract enlargement by transvalvular patch and pulmonary artery banding were created in 2-month-old piglets (n = 6) to mimic repaired tetralogy of Fallot. Age-matched piglets were used as controls (n = 5). Right ventricular function was evaluated at baseline and 3 and 4 months of follow-up by hemodynamic parameters and electrocardiography. Right ventricular tissue remodeling was characterized using cellular electrophysiologic and histologic analyses. RESULTS: Four months after surgery, right ventricular peak pressure increased to 75% of systemic pressure and pulmonary regurgitation significantly progressed, end-systolic and end-diastolic volumes significantly increased, and efficient ejection fraction significantly decreased compared with controls. At 3 months, the slope of the end-systolic pressure-volume relationship was significantly elevated compared with baseline and controls; a significant rightward shift of the slope, returning to the baseline value, was observed at 4 months, whereas stroke work progressed at each step and was significantly higher than in controls. Four months after surgery, QRS duration was significantly prolonged as action potential duration. Significant fibrosis and myocyte hypertrophy without myolysis and inflammation were observed in the operated group at 4 months. CONCLUSION: Various aspects of early right ventricular remodeling were analyzed in this model. This model reproduced evolving right ventricular alterations secondary to chronic volumetric and barometric overload, as observed in repaired tetralogy of Fallot with usual sequelae, and can be used for therapeutic innovation.

Local preconditioning by thermal stress accelerates microvascular thrombus formation.

Heme oxygenase 1 (HO-1) has been shown to suppress microvascular thrombus formation. Because stress conditioning induces HO-1 and, in addition, the anticoagulant thrombomodulin and thrombospondin 1, we studied the effect of hyperthermic and hypothermic local stress conditioning on microvascular thrombus formation. For local stress conditioning, the hindlimb of Sprague-Dawley rats was subjected to local heating (42.5 degrees C) or cooling (4 degrees C) for 30 min at 24 h before induction of thrombosis. Sham-exposed hindlimbs served as controls. Thrombosis was induced photochemically in arterioles and venules of the preconditioned tissue (muscle, subcutis, and periosteum) by continuous light exposure after injection of a fluorescent dye. Immunohistochemistry revealed that stress conditioning distinctly induced HO-1, thrombomodulin, and thrombospondin 1 but also von Willebrand factor in endothelial cells. Of interest, intravital fluorescence microscopic analysis of the kinetics of thrombus formation could not confirm an antithrombotic effect of stress conditioning but showed, in contrast, a significant acceleration of thrombosis (P < 0.05) in both arterioles and venules of either of the tissues studied. Although hypothermic and hyperthermic stress conditioning induces antithrombotic HO-1, thrombomodulin, and thrombospondin 1, it enhances endogenous thrombogenicity, most probably due to upregulation of the prothrombotic von Willebrand factor. Thus, preconditioning with local stress cannot be considered as a strategy to prevent thrombus formation.

Moderate and chronic hemodynamic overload of sheep atria induces reversible cellular electrophysiologic abnormalities and atrial vulnerability.

OBJECTIVES: The aim of this study was to evaluate the myocardial consequences of a chronic volume overload of the left atrium (LA). BACKGROUND: Atrial dilation is a major risk factor for atrial fibrillation (AF), but the underlying mechanisms are poorly understood. METHODS: A left-right aorto-pulmonary artery shunt (APS) was created in sheep. The cardiopathy was characterized by echocardiography, electrophysiologic testing, and histologic analysis. Cellular action potential (AP) and calcium current (I(Ca)) were recorded by means of microelectrode and patch clamp techniques. RESULTS: Three to four months after surgery, all animals in the APS state had a dilated LA (146.2 +/- 35.4 cm(2)/m(2) vs. 91.7 +/- 10.4 cm(2)/m(2) in the control state; p = 0.0024) but remained in sinus rhythm. Repetitive atrial firing was triggered by a single extra beat in five of six animals in the APS state and in two of six animals in the control state. Moreover, in two animals in the APS state, a single extra beat triggered sustained AF. Myocytes were enlarged and 39.8% showed some degree of myolysis. In animals in the APS state, the AP had no plateau phase or small amplitude and numerous myocytes were unexcitable. The I(Ca) density was 45.2% lower in APS animals than in control animals. Beta-adrenergic stimulation normalized I(Ca) and restored the plateau phase of the AP. After shunt suppression, the electrophysiologic properties of the atria returned to normal. CONCLUSIONS: The APS induced moderate, isolated LA dilation, which was sufficient to cause major changes in cellular electrophysiologic properties and to render the atria vulnerable to fibrillation. These effects were reversed by shunt suppression.

Primary culture of human atrial myocytes is associated with the appearance of structural and functional characteristics of immature myocardium.

We examined changes in the structural and physiological characteristics of human atrial myocytes during primary culture in the presence of serum. Action potentials and ionic currents were recorded in freshly dissociated (FM) and cultured (CM) whole-cell patch-clamped myocytes, alpha-smooth muscle actin, sarcomeric alpha-actinin and beta-myosin heavy chains (beta-MHC) were stained with monoclonal antibodies. From day 5 to day 21, myocytes lost their rod shape, spread and exhibited reorganized sarcomeres. These morphological changes were associated with a marked increase in membrane capacitance (+266%). Both beta-MHC and alpha-smooth muscle actin were expressed in CM but not in FM, indicating a dedifferentiation process. CM were characterized by a lower resting potential (-30 +/- 2 v -60 +/- 4 mV, P < 0.05) and, when repolarized, by a shorter action potential duration (APD) than FM (APD-60: 126.9 v 159.6 ms, P < 0.05). The inward rectifier K+ current was absent in CM, thus explaining the low resting potential. The density of the transient component of the voltage-activated K+ current Ito1 was not modified during culture, while that of the sustained component Isus was increased fourfold. The amplitude of ICa was increased, but its density was unchanged, indicating that CM maintained a normal density of functional calcium channels. Neither the voltage dependence nor the inactivation of ICa was modified in CM. The time constants of inactivation of ICa were unchanged, although the amplitude of the rapidly inactivating component of ICa was increased in CM compared to FM. Moreover, ICa was increased by the beta-adrenergic agonist isoproterenol (1 microM) throughout the culture period. Our results demonstrate that in long-term serum-supplemented culture, adaptation of human atrial myocytes to their new environment is associated with differential alterations of the main ionic currents and phenotypic changes characteristic of immature myocardium.