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 SARA Computing and Networking Services and a mini-Beowulf cluster in her own Department of Theoretical Biology at Utrecht University. 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 co-ordination of how the heart muscle contracts. These vary in seriousness from palpitations to disorders though that are fatal within minutes. Heart rhythm disorders are one of the most frequent causes of death.
Kirsten 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. Kirsten 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 that was defended on 29 November 2004. The programme of the symposium and the complete Ph.D. thesis with animations can be viewed at the Web site of the Department of Theoretical Biology at Utrecht University.