of bradycardia depends on the severity of symptoms, the correlation
of symptoms with the bradycardia, and the presence of possible
reversible causes (see table of causes
of bradycardia ). There are few indications for treatment
of asymptomatic bradycardia.
The American Heart Association guidelines for implantation of
pacemakers (see figures
92c) list the following as universally accepted (class I)
indications in asymptomatic patients:
Third degree AV block with documented asystole of 3 or more
seconds (in sinus rhythm) or escape rates below 40 beats per
minute in awake patients;
3rd degree AV block or 2nd degree AV Mobitz type II block in
patients with bifascicular and trifascicular block;
Congenital 3rd degree AV block with wide QRS escape rhythm,
ventricular dysfunction, or bradycardia markedly inappropriate
Potential (class II) indications for pacing in asymptomatic
patients include the following:
degree AV block with faster escape rates in patients who are
degree AV Mobitz type II block in patients without bifascicular
or trifascicular block,
incidental finding on electrophysiologic study of block below
or with in the His bundle.
bradycardia (even if extreme) is present only during sleep,
pacing usually not indicated.
symptomatic patients the keys to proper decision making are
correlation of symptoms to bradycardia and reversibility of
causative factors (see table of causes
Symptoms definitely related to simultaneous, confirmed bradycardia
that is caused by intrinsic sinus-node dysfunction or AV block,
should be treated by permanent pacing using an internally implanted
pacemaker (see figures
Sinus and AV nodes are relatively resistant to permanent injury
by infarction (cell death due to lack of coronary blood flow)
or infection. Normal function should recover over time. Thus,
sinus bradycardia, or AV nodal block in these settings rarely
require permanent pacing.
Permanent damage occurs more really to the bundle of His. Even
transient complete AV block in the His-Purkinje system due to
infarction or infection justifies the insertion of a pacemaker.
Among those with recurrent unconfirmed syncope and chronic bifascicular
or trifascicular block, pacing is indicated if other likely
causes (i.e. ventricular tachycardia) have been ruled out.
bradycardia due to extrinsic factors require clinical judgement.
A change in drug therapy should be considered if the bradycardia
is due to a drug. But if a substitute drug is not efficacious,
then pacing becomes indicated.
is also indicated with bradycardia-tachycardia syndrome if the
drugs used to control the ventricular rate during atrial arrhythmias
14) cause bradycardia during sinus rhythm.
Atrial based pacing is preferred in patients with sinus-node
dysfunction because it reduces the incidence of atrial fibrillation,
pacemaker syndrome, and formation of blood clots, which can
break away from the heart's walls (embolus) and go to a peripheral
vessel in the brain, legs, or other parts of the body.
Dual chambers pacing (with electrodes in both right atrium and
ventricle) is needed if AV block is also present (see figures
neurocardiac syncope, patient education and drug trials are
indicated before use of pacing.
some cases of more profound bradycardia, reversible causes may
be found responsible and are treatable (see figure 93b).
with atrial fibrillation (a state of marked atrial irritability
causing multiple, rapid, irregular excitation waves to bombard
the AV node and hence rapid heart rates) may have great variability
of heart rates (see figures
In these patients prolonged ventricular pauses may occur frequently.
Many have pauses longer than 2 seconds to 3 seconds. It is felt
that these patients with atrial fibrillation and day time pauses
of up to 2.8 seconds and night time pauses up to 4.0 seconds
should be considered within expected limits. Hence, these episodes
if asymptomatic are treated conservatively before pacemaker