LEAP for advanced cardiac arrhythmia and proarrhythmic risk assessment
There's more to cardiac safety than hERG inhibition and QT prolongation—changes in action potential morphology can reveal electrophysiological effects that repolarization duration alone may miss. Functional assays using human stem cell-derived cardiomyocytes provide additional insight into how compounds affect cardiac depolarization, repolarization, rhythm, and action potential morphology.
In this Coffee Break Webinar, Daniel Millard, PhD, explores how local extracellular action potential (LEAP) recordings extend cardiomyocyte microelectrode array (MEA) assays by providing an action potential-like signal from the same cells and MEA plates used for extracellular field potential recordings.
Learn how LEAP can support automated detection of repolarization abnormalities, quantify action potential morphology, and characterize compound-induced electrophysiological effects associated with proarrhythmic risk.
What will you learn?
- How cardiomyocyte MEA assays measure cardiac field potentials
- How field potential features relate to cardiac depolarization and repolarization
- What the local extracellular action potential (LEAP) signal is and how it is generated
- How LEAP relates field potential measurements to cardiac action potential morphology
- How LEAP can improve automated detection of early afterdepolarizations (EADs)
- How action potential duration and triangulation respond to different ion channel blockers
- How LEAP can complement CiPA-style cardiac safety assays
From CiPA cardiac safety assays to LEAP
The Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative proposed using human stem cell-derived cardiomyocytes as part of a more integrated approach to evaluating drug-induced arrhythmia risk.
One component of this approach uses microelectrode arrays to measure drug-induced electrophysiological changes in beating cardiomyocytes. The cardiomyocyte MEA assay records the cardiac field potential, an extracellular signal generated as cardiac action potentials propagate across a functionally connected cardiomyocyte network.
Features within the field potential enable researchers to quantify aspects of cardiac electrophysiology, including:
- Beat frequency
- Depolarization
- Repolarization timing
- Repolarization irregularities
Building on cardiomyocyte field potential measurements used in the CiPA studies, LEAP technology was developed to provide an additional electrophysiological signal from the same cardiomyocyte cultures.
Explore the CiPA myocyte study to learn more about using hiPSC-derived cardiomyocytes and MEA technology for proarrhythmic risk assessment.
What is a local extracellular action potential (LEAP)?
The local extracellular action potential, or LEAP, is an action potential-like signal generated by transiently enhancing the coupling between a cardiomyocyte and an MEA electrode.
The principle is related to the cell-electrode coupling used in patch-clamp electrophysiology. By changing the coupling between the cell and the electrode, the recorded signal transitions from a conventional extracellular field potential to a LEAP waveform that reflects the morphology of the cardiac action potential.
In the webinar, LEAP recordings are described as having amplitudes between approximately 5 and 20 mV and remaining stable for 10 to more than 20 minutes following induction.
Importantly, the resulting waveform captures features of cardiac action potential morphology, including the plateau phase.
How does LEAP relate field potentials to cardiac action potentials?
Field potential and LEAP recordings provide complementary views of cardiomyocyte electrophysiology.
When the two signals are compared from neighboring electrodes in the same well, the depolarization spike of the field potential corresponds with the upstroke of the LEAP signal. Similarly, the repolarization feature of the field potential corresponds with the end of the plateau phase in the LEAP waveform.
Repolarization irregularities can also be observed across both signal types.
This relationship provides a direct connection between extracellular field potential features and the underlying action potential morphology, helping researchers interpret conventional cardiac MEA measurements in the context of the cardiomyocyte action potential.
Detecting repolarization abnormalities and EADs
Changes in cardiac repolarization are important indicators when evaluating potential proarrhythmic effects.
The high-amplitude LEAP waveform and its representation of the cardiac action potential plateau make features such as repolarization prolongation and early afterdepolarizations (EADs) easier to identify with automated analysis.
In addition to supporting detection of repolarization irregularities, LEAP introduces measurements of action potential morphology that are not directly available from conventional field potential recordings.
These endpoints include action potential triangulation, providing another way to characterize complex changes in cardiac repolarization.
Adding LEAP to a cardiomyocyte MEA workflow
LEAP can be incorporated following a standard cardiomyocyte field potential assay rather than requiring a separate cell model.
In the workflow presented in the webinar, baseline and compound-treated field potential recordings are first collected after the cardiomyocytes equilibrate under controlled environmental conditions. LEAP induction can then be performed across selected electrodes while the plate remains on the MEA system.
The induction phase lasts approximately 10 minutes. Once induction is complete, the resulting LEAP signals can be recorded and analyzed for action potential morphology.
This workflow allows researchers to obtain complementary information from the same cardiomyocytes: conventional extracellular field potential measurements followed by action potential-like LEAP recordings.
Characterizing ion channel pharmacology with LEAP
The webinar demonstrates how LEAP waveforms respond to compounds targeting different cardiac ion currents.
Nifedipine shortens action potential duration
Nifedipine, an L-type calcium channel blocker, progressively shortened the duration of the LEAP signal as concentration increased.
The response reflects the contribution of calcium current to the cardiac action potential plateau and demonstrates how LEAP can capture compound-induced changes in action potential duration and morphology.
E-4031 prolongs repolarization
E-4031, a blocker of the hERG potassium channel, produced a different response. Increasing concentrations initially prolonged repolarization and subsequently generated repolarization irregularities.
The LEAP waveform enables these changes in repolarization to be visualized in the context of the overall cardiac action potential morphology.
Verapamil alters the action potential plateau
Verapamil, which affects both calcium and potassium currents, shortened the LEAP signal and eliminated the action potential plateau in the example presented in the webinar.
Together, these examples demonstrate how compounds targeting different cardiac ion currents can produce distinct electrophysiological phenotypes.
Using action potential triangulation to assess proarrhythmic effects
Action potential duration alone may not capture every electrophysiological change associated with arrhythmia risk.
The webinar compares tolterodine and terodiline, two compounds developed for urinary incontinence. Terodiline was ultimately withdrawn from the market because of its association with torsades de pointes.
Previous action potential recordings from canine Purkinje fibers showed different responses to the two compounds. Tolterodine prolonged the action potential without substantially changing its shape, while terodiline produced significant action potential triangulation.
LEAP recordings from stem cell-derived cardiomyocytes reproduced these distinct response patterns. Tolterodine prolonged action potential duration without altering morphology, while higher concentrations of terodiline produced triangulation.
This example illustrates why measuring action potential morphology alongside duration can provide additional information when characterizing complex electrophysiological responses associated with proarrhythmic risk.
Combining LEAP with electrical pacing
LEAP can also be combined with other functional cardiac electrophysiology approaches.
The webinar demonstrates LEAP recordings during electrical pacing using stimulation electrodes integrated into a multiwell MEA plate. Controlling the cardiomyocyte beat rate while measuring action potential-like signals can provide additional experimental control when evaluating cardiac electrophysiology.
Combining field potential recordings, LEAP, and electrical pacing extends the types of functional measurements that can be collected from stem cell-derived cardiomyocyte cultures.
Expanding functional cardiac safety assessment with LEAP
LEAP adds action potential-like recordings to conventional cardiomyocyte MEA assays using the same cell cultures and MEA plates.
The signal provides a direct relationship between field potential features and cardiac action potential morphology while enabling additional endpoints such as automated EAD detection and action potential triangulation.
Combined with longitudinal MEA measurements and pharmacological testing, these capabilities provide researchers with additional ways to characterize how compounds alter cardiomyocyte electrophysiology and investigate potential proarrhythmic effects.
Watch the webinar to learn how LEAP extends cardiomyocyte MEA assays with action potential morphology measurements for advanced cardiac safety and arrhythmia assessment.
Continue exploring cardiac electrophysiology
Explore scalable cardiac action potential electrophysiology: Learn how LEAP technology enables high-throughput action potential morphology measurements in a newer webinar dedicated to the LEAP assay.
Understand the CiPA framework: Learn what the CiPA myocyte study is and how hiPSC-derived cardiomyocytes and MEA technology have been evaluated for proarrhythmic risk assessment.
Explore the validation results: Review the CiPA validation study results and the multisite evaluation of human stem cell-derived cardiomyocyte assays.
Read the research: Explore the published CiPA pilot study examining cross-site reliability of hiPSC-cardiomyocyte MEA assays.
