Multi-Electrode Array (MEA) Field-Potential and Conduction-Velocity Profiling of hiPSC-Cardiomyocyte Monolayers for Proarrhythmia (CiPA) Screening

Each compound is tested across ≥5 ascending concentrations (half-log spacing) on a minimum of n=4 independent MEA wells (separate monolayers) per concentration, with cumulative within-well dosing (each well serves as its own baseline) plus a separate vehicle-time-control plate to subtract drift. Plate layout is randomized to avoid edge/position bias. Reference positive (dofetilide, E-4031), negative (no effect: e.g., verapamil for FPD), and vehicle controls are included on every plate. Recordings: 5 min baseline, then 5-min equilibration per dose with the last 60 s analyzed. Experiments run on day 20-30 post-differentiation monolayers to ensure stable spontaneous beating.

BSL-2 for human-derived cardiomyocytes; biosafety cabinet for all open culture. Dofetilide and E-4031 are potent cardioactive drugs — handle with nitrile gloves, avoid aerosols/skin contact, and treat dosing solutions as hazardous pharmaceutical waste. DMSO enhances dermal absorption of co-dissolved drugs. PPE: lab coat, nitrile gloves, safety glasses. Drug-containing medium and pipette tips are collected as chemical/biohazard mixed waste per institutional EHS; biological waste is bleached (10% final). MEA probes are cleaned per manufacturer (no autoclave for some plates).

Vehicle/time control: a parallel plate receiving DMSO/medium additions only quantifies time- and handling-dependent FPD/beat drift, which is subtracted from drug effects. Positive proarrhythmia control: dofetilide or E-4031 must produce concentration-dependent FPDc prolongation and arrhythmia events. Positive chronotropy control: isoproterenol must increase beat rate, confirming the monolayer is physiologically responsive. Negative control: vehicle wells should show <10% FPDc change over the full recording. Plate-level QC control: electrode noise and minimum-active-electrode thresholds gate each well in/out before analysis.

Healthy baseline monolayers show beat periods of 0.7-2 s (0.5-1.5 Hz), sharp biphasic field-potential spikes with amplitude >0.3 mV, and conduction velocities of ~10-25 cm/s. Dofetilide/E-4031 prolong FPDc by 10-60% across the tested range with arrhythmia-like events appearing at near-saturating IKr block. Verapamil shortens beat period and minimally changes FPDc. Isoproterenol increases beat rate by 20-100%. Concentration-response curves yield interpretable EC50/IC50 values with Hill fits.

• hiPSC-CMs (commercial e.g. iCell Cardiomyocytes2, or in-house day-20+), >90% cTnT+
• 48- or 24-well CytoView MEA plates (Axion) or equivalent glass MEA
• Fibronectin (50 µg/mL) or Matrigel coating for MEA wells
• Plating medium and maintenance medium per CM source (e.g., RPMI + B-27 complete)
• E-4031 dihydrochloride (IKr blocker), 10 mM stock in water; working 1 nM-1 µM
• Dofetilide, 10 mM stock in DMSO; working 0.1 nM-100 nM
• Verapamil HCl, 10 mM stock; working 1 nM-10 µM
• Isoproterenol (β-agonist positive chronotrope), 1 mM stock; working 1 nM-1 µM
• DMSO (vehicle, kept <0.1% final)
• Sterile-filtered serial dilution plates in maintenance medium

To establish a multi-electrode array (MEA) assay measuring spontaneous and paced extracellular field potentials of hiPSC-derived cardiomyocyte (hiPSC-CM) monolayers, extracting field-potential duration corrected for rate (FPDc, Fridericia/Bazett analog), beat period, spike amplitude, and conduction velocity, and to validate the assay's ability to flag torsadogenic compounds per the CiPA paradigm using reference drugs.

1. Coat MEA wells with fibronectin/Matrigel; plate hiPSC-CMs as a high-density droplet (~3-6 x10^4 cells in 5-10 µL) directly over the electrode field; incubate 1 h before flooding with medium.
2. Maintain monolayers 7-10 days, refreshing medium every 2 days, until uniform synchronous spontaneous beating covers the electrode array (typically day 20-30 of differentiation).
3. On recording day, equilibrate the plate in the MEA reader at 37°C / 5% CO2 for ≥20 min to stabilize beat rate before baseline.
4. Record 5 min baseline spontaneous activity; verify QC (≥6 active electrodes/well, beat period CV <10%).
5. Add the lowest drug concentration (replace ≤10% well volume with concentrated dose to minimize dilution), equilibrate 5 min, record final 60 s.
6. Repeat step 5 cumulatively for each ascending concentration.
7. For conduction velocity, use the propagation map across the electrode grid; for paced experiments, apply biphasic stimulation at fixed cycle length (e.g., 1 Hz) and re-measure FPD.
8. Run a vehicle-only time-control plate in parallel with matched volume additions.

Independent variables: drug identity and concentration; optional pacing cycle length. Dependent variables: beat period, FPD (raw), FPDc (rate-corrected), spike amplitude, conduction velocity, and arrhythmia-event incidence. Controlled variables: temperature (37°C), CO2 (5%), monolayer age/passage, electrode coating lot, plating density, equilibration time, % DMSO (<0.1%), and analysis window (final 60 s/dose). Each well's own baseline is the matched control to reduce inter-well variability.

Repolarization-blocking compounds (e.g., the hERG/IKr blocker E-4031 and dofetilide) will prolong rate-corrected field-potential duration (FPDc) in a concentration-dependent manner and, at higher concentrations, induce arrhythmia-like events (early afterdepolarization-like waveforms, beat irregularity), whereas a multi-channel blocker with balanced inward/outward block (e.g., verapamil) will shorten beat period and minimally affect FPDc, reproducing the CiPA torsadogenic ranking.

Field-potential traces are processed in the MEA vendor software (e.g., AxIS Navigator/Cardiac Analysis) or open tools (e.g., custom Python with detected spike/repolarization markers). FPD is the spike-to-repolarization-peak interval; FPDc is rate-corrected (Fridericia: FPDc = FPD/(beat period)^(1/3)). Per-electrode values are averaged to a well value, then expressed as % change from that well's own baseline. Conduction velocity is computed from the activation-time gradient across electrode positions. Concentration-response data are fit to a 4-parameter Hill equation to derive EC50/IC50 and maximal effect.

1. No or weak beating signal: monolayer not confluent over electrodes or poor coating — replate at higher density directly onto the electrode field and verify fibronectin/Matrigel coating. 2. Unstable/drifting baseline beat rate: insufficient thermal equilibration — extend pre-recording equilibration to ≥30 min and confirm reader holds 37°C/5% CO2. 3. Excessive electrode noise / few active electrodes: ground/contact issue or debris — clean contacts, re-seat the plate, and apply the active-electrode QC gate. 4. No FPDc prolongation with dofetilide: monolayer too immature (low IKr) or dosing too low — use day-25+ monolayers and verify stock concentration/serial dilution. 5. Spontaneous arrhythmias at baseline: monolayer over-aged or stressed — use fresh monolayers and re-check beat-period CV before dosing.

Per-concentration % FPDc change vs vehicle is tested by two-way repeated-measures ANOVA (factors: concentration × treatment) with Dunnett's correction against baseline/vehicle (α=0.05), n≥4 wells/concentration. Arrhythmia incidence is compared by Fisher's exact test. EC50 confidence intervals come from nonlinear-regression fits. Power analysis targets detection of a 10% FPDc change (SD≈6%) at 80% power, α=0.05, giving n≈5 wells/group; replicate across ≥2 cell lots to assess robustness.