Purkinje fiber assay
It is well appreciated that acquired or drug induced-torsade de pointes (TdP), is associated with the generation of long action potential duration (APD)-related early after depolarizations (EADs) and EAD-induced triggered activity. EADs, occurring as oscillations during phase 2 or 3 of the action potential (AP) are potentially arrhythmogenic. PFs are more sensitive to drug-induced long APD and EADs than working ventricular muscle, mainly because of increased sensitivity to hERG inhibition. Consequently EADs are more easily induced in PFs. In agreement with these observations in vitro, in vivo studies show that the initiation of EAD-induced TdP arises in PFs. Therefore, Purkinje fibers appear to play a particularly important role as a generator of EADs in TdP arrhythmias associated with long QT syndrome-type arrhythmias. The cardiac Purkinje fiber is a well-established preparation commonly used in the pharmaceutical industry to evaluate the cardiac electrophysiological effects of drugs known to prolong QT interval. The sensitivity of in vitro preparations to compounds which affect cardiac repolarization may depend on the species, gender, as well as on the nature of the preparation. The physiologically relevant whole-ventricle Purkinje fibers preparation where Purkinje fibers are connected to the surrounding ventricular tissue is a common preparation to assess drug effects on APD. Parameters measured include:
- Action potential duration (APD) at 20, 50 and 90% repolarization
- Upstroke velocity (Vmax)
- Resting membrane potential
- Incidence of early after depolarizations (EADs)
- Dose responses can be generated and various stimulation frequencies can be applied.