Effects Of Biventricular Pacing On Cardiac Function

Both animal and human studies have shown that, in the presence of an intrinsic intraventricular conduction delay, pacing from the left ventricle is ultimately associated with a better cardiac function (compared with sinus rhythm and right ventricular apical pacing). Several clinical trials on biventricular pacing for congestive heart failure without traditional indications for pacing, have been described and are summarized in Fig. 3. Such trials include the InSync registry (13,14), the Multisite Stimulation in Cardiomyopathy (MUSTIC) study (15), and the Multicenter InSync Randomized Clinical Evaluation (MIRACLE) study (16). '

3.1. InSync Registry

The InSync registry is a prospective observational multicenter European and Canadian study that examined the safety

Table 1

Mechanisms of Ventricular Synchronization Therapy

• Improved contraction pattern

♦ Improves interventricular synchrony

♦ Reduces paradoxical septal wall motion

♦ Improves left ventricular regional wall motion

♦ Lowers end-systolic volumes

♦ Improves left ventricular dp/dt

• Atrioventricular interval optimization

♦ Reduces mitral regurgitation

♦ Increases diastolic filling time

♦ Improves left ventricular dp/dt and efficacy of a biventricular pacemaker (with left ventricular pacing leads implanted via cardiac veins) as a supplemental treatment for refractory congestive heart failure (13,14). Between August 1997 and November 1998, there were 103 patients enrolled (with a mean left ventricular ejection fraction of 22% and a mean QRS duration of 178 ms). Over a follow-up period of12 months, 21 patients died. The 12-month actuarial survival was 78% (confidence interval [CI] 70-87%). Nine surviving patients withdrew from the study for miscellaneous reasons during long-term follow-up.

At each point of follow-up over a 12-month period, a significant shortening of QRS duration was observed, and significant improvements were found in mean New York Heart Association (NYHA) functional class, a 6-min walk test and a quality-of-life score. In the 46 patients with complete echocardiography data, ejection fractions increased from 21.7 ± 6.4% at baseline to 26.1 ± 9.0% at the last follow-up (p = 0.006). In addition, it was shown that the left ventricular end-diastolic dimensions decreased from 72.7 ± 9.2 to 71.6 ± 9.1 mm (p = 0.233); inter-ventricular mechanical delays decreased from 27.5 ± 32.1 to 20.3 ± 25.5 ms (p = 0.243); mitral regurgitation apical four-chamber areas decreased from 7.66 ± 5.5 to 6.69 ± 5.9 cm2 (p = 0.197); and left ventricular filling times increased from 363 ± 127 to 408 ± 111 ms (p = 0.002).

The investigators concluded that long-term cardiac resyn-chronization could be safely and reliably achieved by trans-venous atrial synchronized right and left ventricular pacing. These changes were accompanied by clinically relevant improvements in functional status and quality-of-life scores, as well as a measurable increase in left ventricular performance. Incorporating biventricular pacing in an implantable cardioverter-defibrillator system, when indicated, is feasible and leads to an improvement of heart failure symptoms (17).

3.2. MUSTIC Trial

The MUSTIC trial employed a single-blinded crossover study design (15). In total, 67 patients were enrolled from 15 centers in Europe. All patients had significant heart failure caused by either idiopathic or ischemic left ventricular systolic dysfunction (ejection fraction of less than 35%) and a left ventricular end-diastolic diameter of more than 60 mm. All patients were also in sinus rhythm with a QRS duration of more than 150 ms, and none had a standard indication for pacemaker or defibrillator implantation. Forty-eight patients completed the 6-month randomized crossover study.

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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