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Biventricular Pacing in Patients with
Heart Failure
There are approximately 4.8 million patients with congestive heart
failure (CHF) in the United States, and 400,000 to 700,000 new cases
present each year. Congestive heart failure is a difficult condition to
treat and it remains the most frequent cause of hospital admissions in the
Medicare population. The cost of caring for CHF patients in United States,
including physician visits, medications, hospital related costs, is
between 10-30 billion dollars. Despite recent therapeutic advances, CHF is
a direct or contributing cause of up to 250,000 deaths per year. Half of
the patients with CHF die from left ventricular pump dysfunction and half
dying suddenly from ventricular arrhythmias.
Recent advances in the treatment of CHF with medications, including
angiotensin-converting enzyme (ACE) inhibitors, beta-blockers (Carvedilol,
Bisoprolol, Metoprolol), Hydralazine with nitrates, and Spironolactone
have resulted in significantly improved survival rates. The antiarrhythmic
agent Amiodarone may improve survival in nonischemic cardiomyopathy, but
no improvement in survival has been demonstrated in patients with ischemic
cardiomyopathy. Other antiarrhythmic agents may worsen survival, have
neutral effects on survival, or have not been well studied.
Although many medications have been clinically beneficial, they fall
short of clinician’s expectations and as a result consideration has
turned to procedures and devices as additional heart failure therapy.
There has been recent enthusiasm for complex pacing, such as
biventricular pacing (pacing both pumping chambers of the heart) in
congestive heart failure patients. 30% to 50% of patients with CHF have interventricular
conduction defects. These conduction abnormalities lead to a
discoordinated contraction of an already failing and inefficient heart.
Even the delayed activation of the left ventricle when the right ventricle
alone is paced, leads to significant dyssynchrony in left ventricular
contraction and relaxation.
In 1986, in a canine study of pacing, Burkhoff noted that left
ventricular pressure decreased in a linear fashion as the QRS duration
increased. Since then, several investigators have hypothesized that
biventricular pacing could provide a more coordinated pattern of
contraction than the dyssynchronous ventricular activation which occurs in
patients with interventricular conduction defects (common in patients with
CHF). Preliminary studies of this "biventricular pacing" have
yielded encouraging results.
The MUSTIC trial, which was recently published, demonstrated that
biventricular pacing might improve symptoms and quality of life in
selected patients with CHF. 48 patients with class III CHF and QRS
duration of greater than 150 milliseconds were treated for three months
with biventricular pacing and then compared to an inactive pacing phase.
With biventricular pacing, the mean distance walked in 6-minutes increased
by 23%, quality-of-life score improved by 32%, peak oxygen uptake
increased by 8%, and hospitalizations were reduced by two-thirds. Active
pacing was preferred by 85% of the patients.
Because ventricular arrhythmias continue to threaten CHF patients and
many antiarrhythmic agents have not been well suited, a sophisticated
implantable cardioverter-defibrillator (ICD) has shown encouraging
results. Biventricular pacing in combination with ICDs demonstrates a
trend toward improved survival. The expanded use of biventricular pacing
in combination with an ICD as a prevention tool will depend on the results
of several ongoing trials. Currently, there are several hurdles, which
stand in the way of this therapy. Advances in lead design, increased
experience, and the use of this procedure in patients who are not as sick
should make this procedure less intimidating and more time-efficient. The
Food and Drug Administration is reviewing the data with this technology.
See
related article about this technology in Helena |
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