Timing of depolarization and contraction in the paced canine left ventricle: model and experiment.
Timing of depolarization and contraction in the paced canine left ventricle: model and experiment.
复制标题
起搏犬左心室除极和收缩的时间：模型和实验。
DOI：
10.1046/j.1540.8167.90310.x
复制
发表时间：
2003
影响因子：
2.7
通讯作者：
Arts,Theo
中科院分区：
文献类型：
--
作者：
Kerckhoffs,RoyCP;Faris,OwenP;Bovendeerd,PeterHM;Prinzen,FritsW;Smits,Karel;McVeigh,ElliotR;Arts,Theo
Introduction:For efficient pump function, contraction of the heart should be as synchronous as possible. Ventricular pacing induces asynchrony of depolarization and contraction. The degree of asynchrony depends on the position of the pacing electrode. The aim of this study was to extend an existing numerical model of electromechanics in the left ventricle (LV) to the application of ventricular pacing. With the model, the relation between pacing site and patterns of depolarization and contraction was investigated.Methods and Results:The LV was approximated by a thick‐walled ellipsoid with a realistic myofiber orientation. Propagation of the depolarization wave was described by the eikonal‐diffusion equation, in which five parameters play a role: myocardial and subendocardial velocity of wave propagation along the myofibercmandce; myocardial and subendocardial anisotropyamandae; and parameterk, describing the influence of wave curvature on wave velocity. Parameterscm,ae, andkwere taken from literature. Parametersamandcewere estimated by fitting the model to experimental data, obtained by pacing the canine left ventricular free wall (LVFW). The best fit was found withcm= 0.75 m/s,ce= 1.3 m/s,am= 2.5,ae= 1.5, andk= 2.1 × 10−4m2/s. With these parameter settings, for right ventricular apex (RVA) pacing, the depolarization times were realistically simulated as also shown by the wavefronts and the time needed to activate the LVFW. The moment of depolarization was used to initiate myofiber contraction in a model of LV mechanics. For both pacing situations, mid‐wall circumferential strains and onset of myofiber shortening were obtained.Conclusion:With a relatively simple model setup, simulated depolarization timing patterns agreed with measurements for pacing at the LVFW and RVA in an LV. Myocardial cross‐fiber wave velocity is estimated to be 0.40 times the velocity along the myofiber direction (0.75 m/s). Subendocardial wave velocity is about 1.7 times faster than in the rest of the myocardium, but about 3 times slower than as found in Purkinje fibers. Furthermore, model and experiment agreed in the following respects. (1) Ventricular pacing decreased both systolic pressure and ejection fraction relative to natural sinus rhythm. (2) In early depolarized regions, early shortening was observed in the isovolumic contraction phase; in late depolarized regions, myofibers were stretched in this phase. Maps showing timing of onset of shortening were similar to previously measured maps in which wave velocity of contraction appeared similar to that of depolarization.(J Cardiovasc Electrophysiol, Vol. 14, pp. S188‐S195, October 2003, Suppl.)
