Multisite stimulation for correction of cardiac asynchrony

Cardiac electrical stimulation as primary or adjunctive treatment of congestive heart failure is entering its second decade of existence. Initial trials of conventional DDD pacing1-5 were followed by bifocal right ventricular stimulation.6 The concept of multisite stimulation for haemodynamic support was introduced in 1994.7 8 Various studies have already reported the benefits of this method,9 10 or are in progress.11 The transition from conventional DDD pacing to multisite stimulation was not fortuitous. Successive “advances” in the design of cardiac pacing systems have aimed at correcting anomalies in the sequence of cardiac chamber activation, as well as in the synchronisation of the various phases of myocardial contraction and relaxation. The phenomenon of asynchrony is a consequence of progressive, global or focal degradation of the myocardium. One can easily visualise interstitial fibrosis gradually replacing areas of normal myocardium, and causing heterogeneous propagation of cardiac electrical activity. Such heterogeneity combines, to various degrees, three consecutive atrioventricular, interventricular, and intraventricular asynchrony levels. Among various analytical and modelling methods, Doppler echocardiography is preferred for its ease of application in day to day practice.12 The oldest concept, that of desynchronised atrioventricular sequential activation, applies only to sinus rhythm. It is the product of a mismatch between end of atrial systole and onset of ventricular systole, sometimes facilitated by a disorder of atrioventricular conduction or QRS prolongation. It may be simply described as an abbreviated ventricular filling time with respect to the complete cardiac cycle, and, on occasion, by early passive ventricular filling flow superimposed on atrial systole dependent flow. Dual chamber pacing, by linking ventricular to atrial activation, normalises flow patterns of ventricular filling, provided atrial contraction …