Relationship between negative inotropic and chronotropic effects of tocainide and five class I antiarrhythmic drugs in the coronary perfused guinea-pig heart

Bioengineering an electro-mechanically functional miniature ventricular heart chamber from human pluripotent stem cells

Tissue engineers and stem cell biologists have made exciting progress toward creating simplified models of human heart muscles or aligned monolayers to help bridge a longstanding gap between experimental animals and clinical trials. However, no existing human in vitro systems provide the direct measures of cardiac performance as a pump. Here, we developed a next-generation in vitro biomimetic model of pumping human heart chamber, and demonstrated its capability for pharmaceutical testing. From human pluripotent stem cell (hPSC)-derived ventricular cardiomyocytes (hvCM) embedded in collagen-based extracellular matrix hydrogel, we engineered a three-dimensional (3D) electro-mechanically coupled, fluid-ejecting miniature human ventricle-like cardiac organoid chamber (hvCOC). Structural characterization showed organized sarcomeres with myofibrillar microstructures. Transcript and RNA-seq analyses revealed upregulation of key Ca²⁺-handling, ion channel, and cardiac-specific proteins in hvCOC compared to lower-order 2D and 3D cultures of the same constituent cells. Clinically-important, physiologically complex contractile parameters such as ejection fraction, developed pressure, and stroke work, as well as electrophysiological properties including action potential and conduction velocity were measured: hvCOC displayed key molecular and physiological characteristics of the native ventricle, and showed expected mechanical and electrophysiological responses to a range of pharmacological interventions (including positive and negative inotropes). We conclude that such "human-heart-in-a-jar" technology could facilitate the drug discovery process by providing human-specific preclinical data during early stage drug development.

Lack of selectivity for ventricular and ischaemic tissue limits the antiarrhythmic actions of lidocaine, quinidine and flecainide against ischaemia-induced arrhythmias

The antiarrhythmic effectiveness, electrocardiographic and haemodynamic properties of three representative class I antiarrhythmics have been investigated in anaesthetized rats. Quinidine, lidocaine and flecainide were chosen as representatives of class Ia, Ib and Ic, respectively. Lidocaine showed the greatest frequency and 'ischaemia' dependency and a high dose provided complete protection against ischaemic arrhythmias induced by coronary artery occlusion. Flecainide showed the least frequency and ischaemia dependency and the least antiarrhythmic effectiveness. Quinidine was only slightly more effective than flecainide. The three drugs were approximately equi-potent in lowering blood pressure which limited the maximum dose that could be tested. The highest dose of lidocaine also caused convulsions in conscious animals. Thus, while lidocaine had selectivity for ischaemic tissue, and for high frequencies, the central nervous system and cardiovascular toxicity limited its usefulness against ischaemia-induced arrhythmias. Quinidine and flecainide's lack of selectivity for ischaemia, and/or high frequencies, probably accounted for their limited antiarrhythmic actions against ischaemia-induced arrhythmias. This study emphasizes that class I drugs can only provide useful protection against ischaemia-induced arrhythmias if they have marked cardiac selectivity as well as selectivity for ischaemic cardiac tissue.