Mechanical perturbation control of cardiac alternans

Pericardial Tamponade and Berger's Disease: An Unusual Association

Cardiac tamponade is considered a medical emergency because a patient can deteriorate easily and die of cardiac arrest if the fluid is not drained immediately. The most common etiologies are the same as pericarditis as fluid accumulates due to pericardial inflammation, including infection, malignancy, trauma, iatrogenic, autoimmune, post-myocardial infarction, radiation, and renal failure. Although the treatment is pericardiocentesis or pericardial window, finding the etiology responsible for the development of pericardial effusion is important. Here, we describe the case of a 40-year-old female who presented to the emergency department with a chief complaint of severe epigastric pain of a two-day duration that was associated with multiple episodes of nausea, vomiting, dysphagia, and severe shortness of breath (New York Heart Association III). The patient was eventually diagnosed with cardiac tamponade as a cause of her dyspnea, as a two-dimensional cardiac echocardiogram detected a large pericardial effusion (>2 cm) with echocardiographic indications for cardiac tamponade with severe pulmonary hypertension. The patient underwent a therapeutic pericardial window with drainage of 250 mL of pericardial fluid. Ultrasound of the abdomen focusing on the kidneys showed an atrophic and echogenic right kidney with a bidirectional flow in the hepatic veins, suggestive of right heart failure. Subsequently, she underwent a kidney biopsy that showed diffuse mesangial proliferative glomerulonephritis with segmental sclerosing features consistent with IgA nephropathy, associated with tubular atrophy, interstitial fibrosis, interstitial inflammation, and moderate arteriosclerosis. The patient was diagnosed with stage V chronic kidney disease secondary to IgA nephropathy. IgA nephropathy is usually common in Caucasian or Asian males in their teens and late 30s, with hematuria as a usual presentation. This case is unique as cardiac tamponade with renal failure is rarely the presenting symptom of IgA nephropathy.

A Simulation Study of the Role of Mechanical Stretch in Arrhythmogenesis during Cardiac Alternans

The deformation of the heart tissue due to the contraction can modulate the excitation, a phenomenon referred to as mechanoelectrical feedback (MEF), via stretch-activated channels. The effects of MEF on the electrophysiology at high pacing rates are shown to be proarrhythmic in general. However, more studies need to be done to elucidate the underlying mechanism. In this work, we investigate the effects of MEF on cardiac alternans, which is an alternation in the width of the action potential that typically occurs when the heart is paced at high rates, using a biophysically detailed electromechanical model of cardiac tissue. We observe that the transition from spatially concordant alternans to spatially discordant alternans, which is more arrhythmogenic than concordant alternans, may occur in the presence of MEF and when its strength is sufficiently large. We show that this transition is due to the increase of the dispersion of conduction velocity. In addition, our results also show that the MEF effects, depending on the stretch-activated channels’ conductances and reversal potentials, can result in blocking action potential propagation.

Effects of mechano-electrical feedback on the onset of alternans: A computational study

Cardiac alternans is a heart rhythm instability that is associated with cardiac arrhythmias and may lead to sudden cardiac death. The onset of this instability, which is linked to period-doubling bifurcation and may be a route to chaos, is of particular interest. Mechano-electric feedback depicts the effects of tissue deformation on cardiac excitation. The main effect of mechano-electric feedback is delivered via the so-called stretch-activated ion channels and is caused by stretch-activated currents. Mechano-electric feedback, which is believed to have proarrhythmic and antiarrhythmic effects on cardiac electrophysiology, affects the action potential duration in a manner dependent on cycle length, but the mechanisms by which this occurs remain to be elucidated. In this study, a biophysically detailed electromechanical model of cardiac tissue is employed to show how a stretch-activated current can affect the action potential duration at cellular and tissue levels, illustrating its effects on the onset of alternans. Also, using a two-dimensional iterated map that incorporates stretch-activated current effects, we apply linear stability analysis to study the stability of the bifurcation. We show that alternans bifurcation can be prevented depending on the strength of the stretch-activated current.