Sudden Cardiac Death: A Problem in Physics

My collaborator: Johannes Breuer (IMSc-Chennai and TU-Berlin)

``Dying

Is an art, like everything else."

~ Sylvia Plath

In Lady Lazarus, Sylvia Plath called dying an art; we however see dying, or at least, death through sudden cardiac arrest (the commonest cause of death in the developed world) as a science, well-understood in parts but still with many mysteries.

One of the less well-understood chapters of cardiac arrhythmia is how defibrillation works. In standard treatment of ventricular fibrillation, where essentially the individual cells of the ventricles are being excited without any coordination so that the heart stops contracting, a very large electric current is passed through the heart within a very brief time interval, in the expectation that this will force all cells into the resting state together, allowing the sinus node to again take over. However, such a method is not only extremely painful - but also likely to cause severe burns in heart muscle, creating scar tissue. These scars will in the future act as the nucleating centre for further arrhythmic activity. The holy grail of arrhythmia research is to come up with a low-amplitude alternative to defibrillation.

Controlling Ventricular Fibrillation by biphasic stimulation at a single point

Following our previous work on spatially extended control of Ventricular Fibrillation, we are now trying to devise control methods which can be applied locally. The advantages and immediate applicability of such a control scheme is obvious: we need to use only a single point electrode, which essentially means that conventional ICDs can be used without any hardware modifications. It is the nature of electrical perturbations that are used which need to be changed: instead of one intense shock applied for a few miliseconds, this will call for very low-amplitude pulses but applied for a few seconds. Recently, we have been looking at great depth in the results of H. Zhang, G. Hu and B. Hu, Phys Rev E 68, 026134 (2003). Johannes has redone the simulations reported in this paper for control on the Panfilov model. Following are a few instantaneous snapshots of the control method in action from the simulation by Johannes.


after 10 time units	after 1000 time units

after 2000 time units	after 3000 time units

after 4000 time units	after 4330 time units

The control pulses are sinusoidal - if the time-period of the cycle is T, then the perturbation is depolarizing (i.e., positive in sign) for T/2 time, and repolarizing (i.e., negative) for the other half of the period. In the figures above control is applied over a 6x6 grid of cells in the centre of the simulation domain. By 4330 time units we observe that the system is essentially free of all spiral defects.

We have found the mechanism by which this control works. This allows us to look at the effects of various wave-shapes in controlling VF. In fact, we have found that sinusoidal wave shape is not the best candidate for such control.