The strength-interval curve for blood vessels

Wavefronts from virtual-electrodes, in response to field-stimulation, are thought to be the main mechanism behind the success of low-energy defibrillation protocols. In this work the concept of the strength-interval curve, usually associated with uni-polar stimulation, is extended to field-stimulation for specific geometrical features — in this case blood-vessels (with realistic fibre architecture and vessel walls) — as the coronary vasculature is known to be an important source of virtual-electrode induced wavefronts. It is shown that, because there is no concept of anodal or cathodal responses in field-stimulation, there is only one strength-interval curve for blood-vessels, and the usual phenomena of make and break excitations are observed for different diastolic intervals. Break excitations occur because regions of de and hyper-polarization are in close proximity due to the resultant virtual-electrode pattern, and they allow excitation at lower field-strengths while the surrounding tissue is relatively refractory. This effect may be important for optimizing low-energy defibrillation protocols.