14th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 2000

Jan. 29 - Feb. 5, 2000
Marilleva, Trento, Italy

RT-116

Rationale for multi-site biventricular pacing to treat refractory heart failure

J. Claude Daubert, Christine Alonso, Philippe Mabo, Christophe Leclerq.
Département de Cardiologie et Maladies Vasculaires, Centre Cardio-Pneumologique, Hôpital Pontchaillou - CHU, Rennes, France

Rationale of biventricular pacing: electromechanical correlates in chronic heart failure

The purpose of multi-site biventricular pacing is to correct the sometimes major electromechanical abnormalities that result from conduction disorders associated with chronic left ventricular systolic dysfunction.

Conduction disorders in chronic LV systolic dysfunction

Anatomoclinical studies, especially the Wilensky’s study⁶, have shown the high prevalence of conduction disorders in patients with chronic LV systolic dysfunction, and their progression over time with an independent prognostic value. AV conduction and intraventricular conduction are particularly concerned. The PR interval increases progressively and is significantly prolonged (³200 ms) in 60% of patients at the end-stage of the disease. It has been shown that 1st or 2nd degree AV block was an independent risk factor of cardiac death in patients with dilated cardiomyopathy⁷. In the same way significant increase of QRS duration is observed in the course of follow-up and reflects the development of progressive intraventricular conduction delay (IVCD). In the Wilensky’s study⁶ 27% of patients had QRS width ³150 ms with peaks up to 200 ms on the last ECG recording before death. IVCD has also been shown as independent mortality risk factor in patients with chronic LV systolic dysfunction^8-11.

ELECTROMECHANICAL CONSEQUENCES

These conduction disorders have a significant impact on cardiac performance.

The lengthening of the PR interval, be it apparent or concealed, induces atrio-ventricular desynchronization, hence shorter ventricular filling time and reduced or even suppressed left atrial contribution to ventricular filling, as often reflected by the single-pulse aspect of the mitral Doppler flow resulting from the superimposition of wave A and wave E⁵.

The haemodynamic consequences of abnormal LV activation in patients with DCM have been explored in depth by Xiao et al^12,13. That study conducted in 50 patients revealed a positive correlation between QRS duration and Q wave delay at LV pressure peak and the interval between the Q wave and the peak +dP/dT. In contrast, QRS duration ant the +dP/dT value were negatively correlated. These data showed that the longer the QRS duration, the longer the duration of LV isovolumetric contraction and relaxing time, hence the more altered the LV pump function was. Also, the increased isovolumetric contraction and relaxation times of the left ventricle induced a shortening of filling time in patients whose QRS duration was particularly long. Finally, abnormal activation sequence may play a role in increasing mitral regurgitation: Xiao et al¹³ and Nishimura et al⁵ found a positive correlation between mitral regurgitation time and QRS duration on the one hand, and PR interval duration on the other hand. In addition, left diastolic atrio-ventricular gradient is a common occurrence in AV conduction disorders and may result in diastolic mitral regurgitation.