Implication of frequency-dependent protocols in antiarrhythmic and proarrhythmic drug testing

Area of Science:

• Electrophysiology
• Cardiology
• Pharmacology

Background:

• Electrophysiological effects of cardioactive drugs often depend on stimulation frequency.
• Class I antiarrhythmic agents and calcium channel blockers show rate-dependent effects.
• Action potential duration (APD) changes can exhibit 'reverse rate-dependency'.

Purpose of the Study:

• To investigate the relationship between drug effects on APD, short-term variability (SV), and cardiac arrhythmias.
• To introduce and define 'relative variability' to isolate drug-specific SV changes.
• To explore the common mechanisms linking reverse rate-dependency, SV, and afterdepolarizations.

Main Methods:

• Analysis of rate-dependent effects of cardioactive drugs on cardiac electrophysiology.
• Introduction of 'relative variability' to quantify drug-induced changes in APD variability.
• Categorization of arrhythmias based on heart rate (tachycardia, bradycardia).

Main Results:

• Drug-induced changes in APD duration show reverse rate-dependency.
• Short-term variability (SV) of APD is a proarrhythmic mechanism influenced by drugs.
• Relative variability increases with blockers of I_Ca, I_Kr, I_Ks and elevated cytosolic Ca²⁺.
• Tachycardia-induced Ca²⁺ overload causes delayed afterdepolarizations.
• Bradycardia is associated with early afterdepolarizations (EADs).

Conclusions:

• Reverse rate-dependency of APD, increased SV, and EAD incidence share common underlying mechanisms.
• Understanding these relationships is crucial for predicting drug-induced arrhythmias.
• Drug effects on APD variability and rate-dependency are key factors in cardiac arrhythmia development.