Circadian rhythms of early afterdepolarizations and ventricular arrhythmias in a cardiomyocyte model

AO_SCPLOWBSTRACTC_SCPLOWSudden cardiac arrest is a malfunction of the hearts electrical system, typically caused by ventricular arrhythmias, that can lead to sudden cardiac death (SCD) within minutes. Epidemiological studies have shown that SCD and ventricular arrhythmias are more likely to occur in the morning than in the evening, and laboratory studies indicate that these daily rhythms in adverse cardiovascular events are at least partially under the control of the endogenous circadian timekeeping system. However, the biophysical mechanisms linking molecular circadian clocks to cardiac arrhythmogenesis are not fully understood. Recent experiments have shown that L-type calcium channels exhibit circadian rhythms in both expression and function in guinea pig ventricular cardiomyocytes. We developed an electrophysiological model of these cells to simulate the effect of circadian variation in L-type calcium conductance. We found that there is a circadian pattern in the occurrence of early afterdepolarizations (EADs), which are abnormal depolarizations during the repolarization phase of a cardiac action potential that can trigger fatal ventricular arrhythmias. Specifically, the model produces EADs in the morning but not at other times of day. We show that the model exhibits a codimension-2 Takens-Bogdanov bifurcation that serves as an organizing center for different types of EAD dynamics. We also simulated a 2-D spatial version of this model across a circadian cycle. We found that there is a circadian pattern in the breakup of spiral waves, which represents ventricular fibrillation in cardiac tissue. Specifically, the model produces spiral wave breakup in the morning but not in the evening. Our study is the first to propose a link between circadian rhythms and EAD formation and suggests that the efficacy of drugs targeting EAD-mediated arrhythmias may depend on the time of day that they are administered. Significance StatementWhy are life-threatening cardiac arrhythmias more likely to occur in the morning than in the evening? The electrical properties of the heart exhibit daily rhythms due to molecular circadian clocks within cardiomyocytes. Our computational model of ventricular myocytes shows that clock-controlled expression of a voltage-gated calcium ion channel leads to early afterdepolarizations (EADs) at certain times of the day. EADs, in which the membrane potential of a cardiomyocyte depolarizes a second time before fully repolarizing, can trigger arrhythmias. To our knowledge, this is the first study linking the circadian clock to EAD formation. Our results suggest that the efficacy of anti-arrhythmic medications targeting this calcium ion channel may depend on the time of day the drug is taken.