Model simulates dynamics of heart rhythm disorders

Dutch researcher Kirsten ten Tusscher has developed a model that can simulate the electrical behaviour of the heart during heart rhythm disorders. One of the things her model revealed is that the electrical activity of the heart during a rhythm disorder is much less chaotic than was originally thought.

Kirsten ten Tusscher first of all made a model that described the electrical behaviour of individual human heart muscle cells. She demonstrated that the behaviour of this model corresponded well with results from experiments on human heart cells. The source code of this cell model is freely available on Internet.

The researcher then used her new model to simulate the behaviour of 13.5 million individual grid points, which together form the anatomy of a human heart. As the model is extremely large and requires a considerable amount of calculating power, she used the TERAS supercomputer of the SARA and a mini-Beowulf cluster in her own department. With this she studied the behaviour of electrical wave patterns during certain rhythm disorders in the human heart.

Heart rhythm disorders are abnormalities in the timing, sequence and coordination of how the heart muscle contracts. These vary in seriousness from palpitations though to disorders that are fatal within minutes. Heart rhythm disorders are one of the most frequent causes of death.

Ten Tusscher focused on two rhythm disorders. In ventricular tachycardia, the heart ventricles contract more frequently than normal. Less blood flows out of the ventricles and the supply of oxygen to the body is reduced. In ventricular fibrillation, the ventricles no longer contract coherently. Due to the reduced pumping action, almost no blood leaves the ventricles. As a result, the body hardly receives any more oxygen and death ensues within minutes.

Spiral-shaped electrical waves rotating at a high frequency can result in a more rapid contraction of the heart. Ventricular fibrillation is caused by spiral waves degenerating into a chaotic pattern of many small waves. Ten Tusscher demonstrated that in a healthy heart, stable three-dimensional spiral waves arise after the administration of several large electrical impulses. Under modified model conditions, the same electrical impulses were found to result in degenerating spiral waves that lead to fatal fibrillation.

Furthermore, the theoretical biologist discovered that during fibrillation, only about six of these spiral waves are present in the heart, whereas it had previously been assumed that this number lay somewhere between 40 and 110. This means that the wave dynamics during fibrillation are much less chaotic than was previously thought.

Kirsten ten Tusscher’s project was funded by the Netherlands Organisation for Scientific Research (NWO) and formed part of the NWO programme ’Non-Linear Systems’. NWO sponsored a mini-symposium in conjunction with Kirsten ten Tusscher’s defence of her doctoral thesis.