Introduction

Despite significant advancements in pharmacological therapy, mortality continues to remain high in patients with congestive heart failure (1). Much attention has been paid to optimization of pacing modalities for patients with left ventricular dysfunction when ventricular pacing is required. Patients with congestive heart failure frequently have symptomatic chro-notropic incompetence, sinus node dysfunction, or atrioven-tricular block, all of which are class I indications for cardiac pacing (2). In addition, atrial fibrillation afflicts 10 to 30% of patients with congestive heart failure.

It is well known that atrioventricular nodal ablation plus pacemaker insertion is necessary in patients with refractory atrial fibrillation and uncontrolled ventricular rates. In patients with atrial fibrillation, studies indicated that dual-chamber pacing with a short atrioventricular delay was associated with better cardiac performance. However, this observation was not confirmed in subsequent short- and long-term studies (3,4).

From: Handbook of Cardiac Anatomy, Physiology, and Devices Edited by: P. A. Iaizzo © Humana Press Inc., Totowa, NJ

The ventricular pacing lead of a single- or dual-chamber pacemaker has traditionally been placed without concern for hemodynamic consequences at the right ventricular apex because of ease of placement and superior stability. However, data have indicated that the right ventricular apical pacing may not be optimal. It is currently believed that pacing from the right ventricular apex is associated with deleterious changes, in both animals and humans, in diastolic and systolic function, myocar-dial perfusion, and neurohumoral status.

For example, Fig. 1 shows the results of one such study that indicated the negative hemodynamic changes during pacing at the right ventricular apex compared with other ventricular sites (5). The detrimental hemodynamic changes associated with right ventricular apical pacing, which are mainly attributed to altered ventricular activation sequences as well as asynchronous contractions, are particularly problematic in patients with the presence of left ventricular dysfunction.

Strong evidence has shown that pacing from the left ventricle (left ventricular pacing alone, biventricular pacing, or multisite left ventricular pacing) was associated with improved hemodynamics in patients with congestive heart failure and

Congestive Cardiac Failure Patient

Fig. 1. Ventricular pacing is associated with decreased cardiac function in normal dogs. Right ventricular apical (RVA), left ventricular apical (LVA), and biventricular apical (LRVA) pacing reduced maximal dp/dt by 20, 14, and 13%, respectively, compared with high right atrial (HRA) pacing. LVB, left ventricular basal pacing; RVB, right ventricular basal pacing. See ref. 5 for further discussion.

Fig. 1. Ventricular pacing is associated with decreased cardiac function in normal dogs. Right ventricular apical (RVA), left ventricular apical (LVA), and biventricular apical (LRVA) pacing reduced maximal dp/dt by 20, 14, and 13%, respectively, compared with high right atrial (HRA) pacing. LVB, left ventricular basal pacing; RVB, right ventricular basal pacing. See ref. 5 for further discussion.

Fig. 2. Effects of pacing configurations on cardiac output during exercise in patients with sinus node dysfunction and normal atrioventricular node function without bundle branch block. Reprinted from ref. 9, © 1995 with permission from Elsevier.

those with (wide QRS duration) and without (narrow QRS duration) intraventricular conduction delay. Hence, the era of biventricular pacing as a therapeutic intervention for patients with congestive heart failure has ensued. Subsequently, a fifth letter has been introduced to describe multisite pacing as a pacemaker mode within the North American Society of Pacing and Electrophysiology (NASPE)/British Pacing and Elec-trophysiology Group (BPEG) Generic Pacemaker Code (NBG Code) (6). For example, the fifth letter "V" in DDDRV represents multisite pacing in the ventricles.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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