A middle-aged engineer was referred for consideration of
pacemaker implantation because of sinus bradycardia. He complained of a fatigue
on moderate activity but denied any dyspnea or chest pain. Previous
investigations had shown normal coronary arteries but a severely reduced EF
(about 25%). A history of heart failure and pacemaker implantation was also
elicited in his brother.
A Holter monitoring revealed severe sinus bradyarrhythmias
with heart rates below 30 bpm during waking hours.
Frequent runs of non-sustained VT were also detected.
A dual chamber pacemaker is definitely indicated in this
setting of dilated cardiomyopathy and severe sinus node dysfunction. Runs of
NSVT are also proven to be an indicator of a high risk for sudden cardiac death
in patients with LV dysfunction and ICD therapy may be the only effective
preventive strategy. Patients with dilated cardiomyopathy and prophylactic ICD
implantation for nonsustained VT in the presence of a left ventricular ejection
fraction of 30% or less are reported to have an incidence of appropriate ICD
interventions similar to that of patients with a history of syncope or sustained
VT or VF.[1]
What about biventricular pacing? Will this patient benefit from
resynchronization therapy?
Cardiac resynchronization through biventricular pacing has
been recently introduced to treat patients with heart failure and
intraventricular conduction delay, similar to complete left bundle branch block.[2,3]
The prevalence of intraventricular conduction delay among patients with heart
failure has been estimated to be as high as 3050% and has been associated with
a poor survival [46]. Ventricular dys-synchrony, due to
interventricular and intraventricular conduction delays, is associated with
paradoxical septal wall motion, pre-systolic mitral regurgitation, reduced
diastolic filling times and delayed activation of free wall segments which may
contract after aortic valve closure [7-10].
Acute studies demonstrated that biventricular pacing, and
possibly left ventricular pacing alone, may improve both systolic and diastolic
function [1118]. Results from early studies of permanent
biventricular pacing have consistently shown acute improvement in symptoms of
dyspnea, fatigue, fluid retention and general well being as well as long-term
reduction of NYHA functional class and number of hospitalization days
[1925]. Biventricular pacing was associated with shortening
of QRS duration, and improvement of left ventricular ejection fraction, exercise
tolerance on a 6-min walking test, maximal oxygen uptake and quality of life
indices, which persisted after 1-year of follow-up [26,27].
On the other hand, there is another group of patients with
heart failure, severe LV dysfunction and narrow QRS complex, like the case under
discussion, who need pacing therapy due to standard indications such as sick
sinus syndrome or high degree AV block. RV pacing in this group has resulted in
dys-synchronous activation of left ventricle, wide QRS more than 200ms and
deterioration of ventricular function. Biventricular pacing in this group is
shown to be feasible, safe and beneficial with improvement in left ventricular
function and symptoms as reported by Cindy M. Backer and his colleagues
[28].
Also in patients with permanent atrial fibrillation and
severe LV dysfunction who need AV junctional ablation or who have an already
implanted conventional RV based pacemaker, implantation or upgrading to a
biventricular pacing system may have the same beneficial results with
improvement of LV function and symptoms of heart failure [29].
References:
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[24] Porciani MC, Puglisi A, Colella A et al. Echocardiographic evaluation of
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[27] William T. Abraham, M.D., Westby G. Fisher, M.D., Andrew
L. Smith, M.D., David B. Delurgio, M.D., Angel R. Leon, M.D., Evan Loh, M.D.,
Dusan Z. Kocovic, M.D., Milton Packer, M.D., Alfredo L. Clavell, M.D., David L.
Hayes, M.D., Myrvin Ellestad, M.D., Robin J. Trupp, M.S.N., Jackie Underwood,
B.S.N., Faith Pickering, B.S.N., Cindy Truex, B.S.N., Peggy McAtee, M.S.N., John
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