@article {2122, title = {Effects of pacing on stationary reentrant activity. Theoretical and experimental study.}, journal = {Circ Res}, volume = {77}, year = {1995}, month = {12/1995}, pages = {1166-79}, abstract = {

It is well known that electrical pacing may either terminate or change the rate and/or ECG appearance of reentrant ventricular tachycardia. However, the dynamics of interaction of reentrant waves with waves initiated by external pacing are poorly understood. Prevailing concepts are based on simplistic models in which propagation occurs in one-dimensional rings of cardiac tissue. Since reentrant activation in the ventricles occurs in two or three dimensions, such concepts might be insufficient to explain the mechanisms of pacing-induced effects. We used numerical and biological models of cardiac excitation to explore the phenomena, which may take place as a result of electrical pacing during functionally determined reentry. Computer simulations of a two-dimensional array of electrically coupled FitzHugh-Nagumo cells were used to predict the response patterns expected from thin slices of sheep ventricular epicardial muscle, in which self-sustaining reentrant activity in the form of spiral waves was consistently initiated by premature stimulation and monitored by means of video mapping techniques. The results show that depending on their timing and shape, externally induced waves may collide with the self-sustaining spiral and result in one of three possible outcomes: (1) direct annihilation of the spiral, (2) multiplication of the spiral, or (3) shift of the spiral center (ie, core). Multiplication and shift of the spiral core were attended by changes in rate and morphology of the arrhythmia as seen by "pseudo-ECGs." Furthermore, delayed termination (ie, termination of the activity one to three cycles after the stimulus) occurred after both multiplication and shift of the spiral center. Both numerical predictions and experimental results support the hypothesis that whether a pacing stimulus will terminate a reentrant arrhythmia or modify its ECG appearance depends on whether the interactions between the externally induced wave and the spiral wave result in the de novo formation of one or more "wavebreaks." The final outcome depends on the stimulus parameters (ie, position and size of the electrodes and timing of the stimulus) as well as on the position of the newly formed wavebreak(s) in relation to that of the original wave.

}, keywords = {Acceleration, Animals, Cardiac Pacing, Artificial, Computer Simulation, Deceleration, Electrocardiography, Models, Cardiovascular, Sheep, Tachycardia, Ventricular}, issn = {0009-7330}, doi = {10.1161/01.RES.77.6.1166}, url = {http://www.ncbi.nlm.nih.gov/pubmed/7586230}, author = {Davidenko, J M and Salomonsz, R and Pertsov, A V and Baxter, Bill and Jalife, J} } @article {2126, title = {Spiral waves of excitation underlie reentrant activity in isolated cardiac muscle.}, journal = {Circ Res}, volume = {72}, year = {1993}, month = {03/1993 }, pages = {631-50}, abstract = {

The mechanism of reentrant ventricular tachycardia was studied in computer simulations and in thin (approximately 20 x 20 x 0.5-mm) slices of dog and sheep ventricular epicardial muscle. A two-dimensional matrix consisting of 96 x 96 electrically coupled cells modeled by the FitzHugh-Nagumo equations was used to analyze the dynamics of self-sustaining reentrant activity in the form of elliptical spiral waves induced by premature stimulation. In homogeneous anisotropic media, spirals are stationary and may last indefinitely. However, the presence of small parameter gradients may lead to drifting and eventual termination of the spiral at the boundary of the medium. On the other hand, spirals may anchor and rotate around small discontinuities within the matrix. Similar results were obtained experimentally in 10 preparations whose electrical activity was monitored by means of a potentiometric dye and high-resolution optical mapping techniques; premature stimulation triggered reproducible episodes of sustained or nonsustained reentrant tachycardia in the form of spiral waves. As a rule, the spirals were elongated, with the major hemiaxis parallel to the longitudinal axis of the cells. The period of rotation (183 +/- 68 msec [mean +/- SD]) was longer than the refractory period (131 +/- 38 msec) and appeared to be determined by the size of the spiral{\textquoteright}s core, which was measured using a newly devised "frame-stack" plot. Drifting of spiral waves was also observed experimentally. Drift velocity was 9.8\% of the velocity of wave propagation. In some cases, the core became stationary by anchoring to small arteries or other heterogeneities, and the spiral rotated rhythmically for prolonged periods of time. Yet, when drift occurred, spatiotemporal variations in the excitation period were manifested as a result of a Doppler effect, with the excitation period ahead of the core being 20 +/- 6\% shorter than the excitation period behind the core. As a result of these coexisting frequencies, a pseudoelectrocardiogram of the activity in the presence of a drifting spiral wave exhibited "QRS complexes" with an undulating axis, which resembled those observed in patients with torsade de pointes. The overall results show that spiral wave activity is a property of cardiac muscle and suggest that such activity may be the common mechanism of a number of monomorphic and polymorphic tachycardias.

}, keywords = {Animals, Computer Simulation, Disease Models, Animal, Dogs, Electrophysiology, Sheep, Tachycardia, Atrioventricular Nodal Reentry, Torsades de Pointes}, issn = {0009-7330}, doi = {10.1161/01.RES.72.3.631}, url = {http://www.ncbi.nlm.nih.gov/pubmed/8431989}, author = {Pertsov, A V and Davidenko, J M and Salomonsz, R and Baxter, Bill and Jalife, J} } @article {2127, title = {Spatiotemporal irregularities of spiral wave activity in isolated ventricular muscle.}, journal = {J Electrocardiol}, volume = {24 Suppl}, year = {1992}, month = {1992}, pages = {113-22}, abstract = {

Voltage-sensitive dyes and high resolution optical mapping were used to analyze the characteristics of spiral waves of excitation in isolated ventricular myocardium. In addition, analytical techniques, which have been previously used in the study of the characteristics of spiral waves in chemical reactions, were applied to determine the voltage structure of the center of the rotating activity (ie, the core). During stable spiral wave activity local activation occurs in a periodic fashion (ie, 1:1 stimulus: response activation ratio) throughout the preparation, except at the core, which is a small elongated area where the activity is of low voltage and the activation ratio is 1:0. The voltage amplitude increases gradually from the center of the core to the periphery. In some cases, however, regular activation patterns at the periphery may coexist with irregular local activation patterns near the core. Such a spatiotemporal irregularity is attended by variations in the core size and shape and results from changes in the core position. The authors conclude that functionally determined reentrant activity in the heart may be the result of spiral waves of propagation and that local spatiotemporal irregularities in the activation pattern are the result of changes in the core position.

}, keywords = {Animals, Cardiac Pacing, Artificial, Fluorescent Dyes, Heart Conduction System, Membrane Potentials, Optics and Photonics, Pericardium, Signal Processing, Computer-Assisted, Tachycardia, Ventricular Function}, issn = {0022-0736}, doi = {10.1016/s0022-0736(10)80029-9}, url = {http://www.ncbi.nlm.nih.gov/pubmed/1552240}, author = {Davidenko, J M and Pertsov, A V and Salomonsz, R and Baxter, Bill and Jalife, J} } @article {2128, title = {Stationary and drifting spiral waves of excitation in isolated cardiac muscle.}, journal = {Nature}, volume = {355}, year = {1992}, month = {01/1992}, pages = {349-51}, abstract = {

Excitable media can support spiral waves rotating around an organizing centre. Spiral waves have been discovered in different types of autocatalytic chemical reactions and in biological systems. The so-called {\textquoteright}re-entrant excitation{\textquoteright} of myocardial cells, causing the most dangerous cardiac arrhythmias, including ventricular tachycardia and fibrillation, could be the result of spiral waves. Here we use a potentiometric dye in combination with CCD (charge-coupled device) imaging technology to demonstrate spiral waves in the heart muscle. The spirals were elongated and the rotation period, Ts, was about 180 ms (3-5 times faster than normal heart rate). In most episodes, the spiral was anchored to small arteries or bands of connective tissue, and gave rise to stationary rotations. In some cases, the core drifted away from its site of origin and dissipated at a tissue border. Drift was associated with a Doppler shift in the local excitation period, T, with T ahead of the core being about 20\% shorter than T behind the core.

}, keywords = {Animals, Dogs, Heart, Mathematics, Membrane Potentials, Models, Biological, Myocardial Contraction, Sheep}, issn = {0028-0836}, doi = {10.1038/355349a0}, url = {http://www.ncbi.nlm.nih.gov/pubmed/1731248}, author = {Davidenko, J M and Pertsov, A V and Salomonsz, R and Baxter, Bill and Jalife, J} }