Introduction: Cardiac wavelength (λ) defines the distance traveled by the propagating wave during the tissue refractory period and is the principle mechanism behind reentry. Reentrant excitation is possible only when λ is less than the reentrant path length. However, the reentrant circuit can also traverse the tissue volume suggesting a need to measure λ in all three dimensions: longitudinal (λL), transverse (λT), and transmural (λM) to accurately represent complexity of the reentrant circuit. We hypothesized that arrhythmia was inducible in the human left ventricle, when the reentrant path volume (VR= λL x λT x λL) was less than or equal to the tissue volume (VT).
Methods: Human LV wedges preparations from donor human hearts (N=6) were optically mapped. The study protocol briefly entailed pacing the tissue, first from the epicardium, and then the transmural surface using a steady-state S1S1 restitution protocol until functional refractory period was reached. The tissue was then treated with pinacidil and the restitution protocol repeated to induce arrhythmia. Wavelength (λ = action potential duration x conduction velocity) was also calculated along the three dimensions.
Results and Discussion: We could induce arrhythmia in all six studies. Arrhythmia was induced when the reentrant path volume was less than the tissue volume (VR < VT). Moreover, the basic cycle length (BCL) at which arrhythmia was induced depended on the pinacidil concentration.
Conclusions: Cardiac wavelength measured in all three directions provides a more accurate marker of the reentrant path. We have demonstrated that arrhythmia can be induced in the human left ventricle wedge when the reentrant path volume is less than or equal to the tissue volume. Consequently, the arrhythmia threshold defined by the minimum reentrant path volume index can predict arrhythmia vulnerability in the human left ventricle.