Biomedical Engineering Reference
In-Depth Information
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35 % with
NYHA functional class III or ambulatory class IV symp-
toms who are receiving optimal recommended medical
therapy and who have frequent dependence on ventricular
pacing.
Resynchronization therapy is not indicated in patients in
NYHA functional class IV for whom there is no obvious
chance to improve the prognosis or quality of life.
CRT is reasonable in patients with an LVEF
£
of life, oxygen consumption during exercise testing, and
6-min walk test).
6.3.1.3 InSync
The InSync study was an uncontrolled, multicenter clinical
study conducted from 1997 to 1998. It initially included 103
patients. The aim was to assess the safety, success rate, and
long-term effects of biventricular pacing. The inclusion cri-
teria were chronic heart failure in NYHA class III/IV, a QRS
width
150 ms, and significant dysfunction of a dilated left
ventricle. Clinical improvement was observed in all the
parameters assessed: the mean QRS complex width decreased
from 180 to 156 ms; the average NYHA classification
decreased from 3.3 to 2.2; the mean distance in the 6-min
walk test changed from 295 to 347 m; and the quality-of-life
questionnaire score changed from 55 to 35 points.
³
6.3.1
Signi fi cant Clinical Studies of CRT
A study of biventricular pacing was published in 1990 [45].
Initial clinical use was described in a pilot study in France in
1995. The results of these and other studies suggested
improvement in some patients with chronic heart failure.
Afterward, large clinical studies followed [ 40, 46, 47 ] .
6.3.1.4 Ventak CHF/Contak CD
This study was started in 1998, published in 2001, and
included 581 patients. They were randomized to either
implantation of a Guidant Ventak CRT-D with an LV lead
implanted via thoracotomy or implantation of Guidant
Contak CRT-D with an LV lead implanted via the coronary
sinus. The inclusion criteria were indications for ICD implan-
tation, NYHA class II/III/IV, an LVEF < 35 %, and a QRS
width > 120 ms. The patients were randomized to have biven-
tricular pacing turned off or turned on for a period of 6
months; afterward, biventricular pacing was turned on in all
patients. After 6 months, there was improvement in the ques-
tionnaire-assessed quality of life and the NYHA class. In the
group receiving resynchronization therapy, there was an
increase in the distance walked during the 6-min walk test
and in maximal oxygen consumption.
6.3.1.1 Vigor in Congestive Heart Failure
(Vigor-CHF)
The Vigor-CHF study was a randomized, controlled study
that was conducted from 1996 to 1998 and included 53
patients of NYHA functional class III/IV. The aim was to
assess cardiac performance by using hemodynamic parame-
ters obtained by invasive measurements and echocardio-
graphic testing. An improvement in hemodynamic parameters
was observed following the implantation of a biventricular
system.
6.3.1.2 Pacing Therapies for Congestive Heart
Failure Study (PATH-CHF)
The randomized, controlled, single-blind PATH-CHF study
that was conducted from 1995 to 1998 included 42 patients
with chronic heart failure secondary to dilated cardiomyopa-
thy in NYHA functional class III/IV, with a QRS > 120 ms,
who were still symptomatic despite adequate medical ther-
apy. The aim was to assess the benefit of LV or biventricular
pacing with an optimal AV delay. The patients were random-
ized to receive pacing therapy (LV or biventricular) for 1
month, followed by a 1-month period of no pacing therapy,
and then crossed over to the other pacing mode for 1 month.
Two dual-chamber pacemakers were used, each of which
had its own sensing bipolar lead in the right atrium and a
unipolar ventricular lead placed either endocardially in the
right ventricle or epicardially in the left ventricle. The pacing
modes for LV or right ventricular pacing and for biventricu-
lar pacing were VDD and VVT, respectively. The study
results showed improvement with biventricular as well as LV
pacing alone. Right ventricular pacing alone was shown to
be inappropriate. The effect of AV delay and of lead place-
ment was confirmed. Improvement occurred in all the param-
eters observed (NYHA class, questionnaire-assessed quality
6.3.1.5 Multisite Stimulation in Cardiomyopathy
Study (MUSTIC)
The MUSTIC multicenter study was conducted from 1996
to 2000. The aim was to assess the clinical efficacy of biven-
tricular pacing in patients with chronic cardiac insufficiency
with a wide QRS complex. This study enrolled 131 patients,
76 of whom were followed up for 12 months. The group
consisted of patients who had a sinus rhythm and no indica-
tion for pacemaker implantation because of arrhythmic
causes (43 patients) or those with chronic atrial fibrillation
who met the criteria for pacemaker implantation because of
a slow ventricular response (33 patients). The patients were
randomized to a 3-month period of biventricular pacing
or no pacing, with a subsequent reciprocal exchange of both
the modes. The study confirmed a significant increase in
the distance walked during the 6-min walk test, an
improved quality of life score, and increased maximal
oxygen consumption.
