Computational modeling of Takotsubo cardiomyopathy: effect of spatially varying ß-adrenergic stimulation in the rat left ventricle.

In Takotsubo cardiomyopathy, the left ventricle shows apical ballooning combined with basal hypercontractility. Both clinical observations in humans and recent experimental work on isolated rat ventricular myocytes suggest the dominant mechanisms of this syndrome are related to acute catecholamine overload. However, relating observed differences in single cells to the capacity of such alterations to result in the extreme changes in ventricular shape seen in Takotsubo syndrome is difficult. By using a computational model of the rat left ventricle, we investigate which mechanisms can give rise to the typical shape of the ventricle observed in this syndrome. Three potential dominant mechanisms related to effects of ß-adrenergic stimulation were considered: apical-basal variation of calcium transients due to differences in L-type and sarco(endo)plasmic reticulum Ca(2+)-ATPase activation, apical-basal variation of calcium sensitivity due to differences in troponin I phosphorylation, and apical-basal variation in maximal active tension due to, e.g., the negative inotropic effects of p38 MAPK. Furthermore, we investigated the interaction of these spatial variations in the presence of a failing Frank-Starling mechanism. We conclude that a large portion of the apex needs to be affected by severe changes in calcium regulation or contractile function to result in apical ballooning, and smooth linear variation from apex to base is unlikely to result in the typical ventricular shape observed in this syndrome. A failing Frank-Starling mechanism significantly increases apical ballooning at end systole and may be an important additional factor underpinning Takotsubo syndrome.

Pathophysiology of takotsubo syndrome: temporal phases of cardiovascular responses to extreme stress.

Takotsubo syndrome (TTS), also known as takotsubo cardiomyopathy, is an acute heart failure syndrome that typically occurs after a period of great emotional stress. The archetypal patient is a postmenopausal woman who presents with chest pain, ST-segment elevation and acute hypokinesia of the apical and middle segment of the left ventricle that extends beyond the territory of a single coronary artery, coupled with hyperkinesia of the basal myocardium. Recent preclinical and clinical studies have shown the importance of high catecholamine levels in precipitating TTS. We propose that this is caused by activation of ß-adrenoceptors and the subsequent activation of a negatively-inotropic pathway, perhaps to protect the heart from catecholamine overload. We explore the pathophysiology of TTS according to its "phases", both preclinically and clinically. This will show that the condition is not one of static apical hypokinesia that simply improves, but rather a dynamic condition that changes as the disease progresses. We hope that further exploration of TTS using its "phases" will aid in its characterization, diagnosis and treatment.

High levels of circulating epinephrine trigger apical cardiodepression in a ß2-adrenergic receptor/Gi-dependent manner: a new model of Takotsubo cardiomyopathy.

BACKGROUND: Takotsubo cardiomyopathy is an acute heart failure syndrome characterized by myocardial hypocontractility from the mid left ventricle to the apex. It is precipitated by extreme stress and can be triggered by intravenous catecholamine administration, particularly epinephrine. Despite its grave presentation, Takotsubo cardiomyopathy is rapidly reversible, with generally good prognosis. We hypothesized that this represents switching of epinephrine signaling through the pleiotropic ß(2)-adrenergic receptor (ß(2)AR) from canonical stimulatory G-protein-activated cardiostimulant to inhibitory G-protein-activated cardiodepressant pathways. METHODS AND RESULTS: We describe an in vivo rat model in which a high intravenous epinephrine, but not norepinephrine, bolus produces the characteristic reversible apical depression of myocardial contraction coupled with basal hypercontractility. The effect is prevented via G(i) inactivation by pertussis toxin pretreatment. ß(2)AR number and functional responses were greater in isolated apical cardiomyocytes than in basal cardiomyocytes, which confirmed the higher apical sensitivity and response to circulating epinephrine. In vitro studies demonstrated high-dose epinephrine can induce direct cardiomyocyte cardiodepression and cardioprotection in a ß(2)AR-Gi-dependent manner. Preventing epinephrine-G(i) effects increased mortality in the Takotsubo model, whereas ß-blockers that activate ß(2)AR-G(i) exacerbated the epinephrine-dependent negative inotropic effects without further deaths. In contrast, levosimendan rescued the acute cardiac dysfunction without increased mortality. CONCLUSIONS: We suggest that biased agonism of epinephrine for ß(2)AR-G(s) at low concentrations and for G(i) at high concentrations underpins the acute apical cardiodepression observed in Takotsubo cardiomyopathy, with an apical-basal gradient in ß(2)ARs explaining the differential regional responses. We suggest this epinephrine-specific ß(2)AR-G(i) signaling may have evolved as a cardioprotective strategy to limit catecholamine-induced myocardial toxicity during acute stress.

Takotsubo cardiomyopathy: the pathophysiology.

Takotsubo cardiomyopathy (TTC) is an acute heart failure syndrome classically characterized by hypocontractile apical and midventricular regions of the left ventricle, with a compensatory hypercontractile base. Available data support the hypothesis that TTC and atypical TTC-like disorders are primarily induced by catecholaminergic overstimulation, with epinephrine playing a crucial role. Knowledge from the available preclinical models should be used to guide the development of potential clinical trials in the most severe cases, where rates of acute morbidity and mortality are highest, and also to prevent recurrence in susceptible individuals.

Hyperthermia as a trigger for Takotsubo syndrome in a rat model.

Takotsubo syndrome is a well-characterized cause of acute yet reversible heart failure associated with periods of intense emotional stress, often mimicking on presentation an acute coronary syndrome. Animal models of Takotsubo syndrome have been developed, either through the application of a stressor, or administration of exogenous catecholamine. We found that in a model of isoproterenol-induced Takotsubo syndrome in anesthetized rats hyperthermia (40-41°C) would occur after the administration of isoproterenol. Maintenance of this hyperthermia would result in an apical hypocontractility typical of the syndrome, whereas prevention of hyperthermia with active cooling to maintain a euthermic core body temperature prevented (but did not subsequently reverse) apical hypocontractility. In vitro experimentation with isolated cardiomyocytes showed no effect of hyperthermia on either baseline contractility or contractility change after beta-adrenoceptor stimulation. We suggest that the rise in body temperature that is characteristic of catecholamine storm may be a component in the development of Takotsubo syndrome.

Corrigendum: Hyperthermia as a trigger for Takotsubo syndrome in a rat model.

[This corrects the article DOI: 10.3389/fcvm.2022.869585.].