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Fig. 3. Clinical trials of cardiac synchronization therapy. *, Investigational device (limited by US federal law to investigational use; ongoing studies, results not yet published; 1, Medtronic (Minneapolis, MN); 2, Guidant Corp. (Indianapolis, IN); 3, St. Jude Medical (St. Paul, MN); 4, Registry; ICD, implantable cardioverter defibrillator. Visit company websites for details.

Fig. 3. Clinical trials of cardiac synchronization therapy. *, Investigational device (limited by US federal law to investigational use; ongoing studies, results not yet published; 1, Medtronic (Minneapolis, MN); 2, Guidant Corp. (Indianapolis, IN); 3, St. Jude Medical (St. Paul, MN); 4, Registry; ICD, implantable cardioverter defibrillator. Visit company websites for details.

Compared with no pacing, biventricular pacing increased patients' 6-min walk distances by 23%, peak oxygen uptakes by 8%, and quality-of-life scores by 32% and decreased hospitalization rates by two-thirds. The authors concluded that atriobi-ventricular pacing significantly improved exercise tolerance and the quality of life in patients with chronic congestive heart failure and intraventricular conduction delay.

A follow-up study to the MUSTIC trial demonstrated that the benefits of biventricular pacing were sustained at a 12-month follow-up (18). The clinical improvement included a 5% increase in ejection fraction and a 45% reduction in mitral regurgitation. Forty-one patients with persistent atrial fibrillation were included in the follow-up study; these patients had an existing indication for pacemakers because of bradycardia or atrioventricular nodal ablation for rate control. Similar clinical improvements were observed in these patients (18).

3.3. MIRACLE Trial

The MIRACLE study was a randomized, double-blind, controlled trial to assess cardiac resynchronization therapy using a biventricular pacing protocol in patients with congestive heart failure. The MIRACLE trial demonstrated that cardiac resynchronization results in significant clinical improvements in patients who have moderate-to-severe heart failure and an intraventricular conduction delay. All patients studied were on stable medical therapies and had no traditional indications for a pacemaker or implantable cardioverter defibrillator. The indications for the MIRACLE study included: (1) moderate or severe congestive heart failure (NYHA functional class III or IV and 6-min walking distance of 450 m or less); (2) left ventricular ejection fraction of 35% or less; (3) widened QRS duration of 130 ms or more; and (4) enlarged left ventricle (left ventricular end-diastolic diameter 55 mm or larger).

From November 1998 through December 2000, there were 571 patients enrolled from 45 centers in the United States and Canada. Of these, 453 patients (228 patients in the pacing therapy group and 225 patients in the control group without pacing) completed the 6-month follow-up study. The primary end points were the determination of NYHA functional class, assessment of quality of life, and results of the 6-min walk test.

Compared with the control group, patients assigned to cardiac resynchronization therapy elicited improvements in the distance walked in 6 min (+39 vs +10 m; p = 0.005), functional class (p < 0.001); quality of life scores (-18.0 vs -9.0points; p = 0.001); times on the treadmill during exercise testing (+81 vs +19 s; p = 0.001); and ejection fractions (+4.6 vs -0.2%; p <

0.001). In addition, fewer patients in the group assigned to cardiac resynchronization therapy required hospitalization (8 vs 15%; p < 0.05) or intravenous medications (7 vs 15%; p < 0.05) for thetreatment of heart failure. There were significant reductions in QRS durations (-20 vs 0 ms;p < 0.001), left ventricular end-diastolic dimensions (-3.5 vs 0.0 mm; p < 0.001), and mitral regurgitant jets (-.7 vs -0.5 cm2; p < 0.001).

In the intention-to-treat analysis, there were 16 deaths inthe control group and 12 deaths in the cardiac resynchronization therapy group. However, this study was not designed to assess whether cardiac resynchronization therapy improved survival in this patient population. Figure 4 shows the Kaplan-Meier estimates of the time to death or hospitalization for worsening heart failure in the control and cardiac resynchronization therapy groups. It was concluded from MIRACLE trial patients in class III and IV systolic heart failure who had intraventricular conduction delays that biventricular pacing (1) was safe and well tolerated; (2) improved quality of life, functional class, and exercise capacity; and (3) improved cardiac structure and function.

How To Keep Your Treadmill Running

How To Keep Your Treadmill Running

Buying a treadmill is hard enough. Choosing the best out of many treadmills in the market is nigh impossible. But once youve got the treadmill youve always wanted, are your worries truly over? Well, they certainly are, but only if you maintain your treadmill properly.

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