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Usually, Mobitz type I AV block is due to excess
CANADIAN JOURNAL OF ANESTHESIA
administration of atropine,2 7 some studies have shown
that atropine that only minimally improved conduction
in the AV node, but markedly increased the sinus rate.
This could increase the degree of block as a result of the
increasing atrial rate.19,20 Spear et al. demonstrated dif-
ferences in the latency, duration and threshold of the SA
node and the AV conduction in response to the sympa-
thetic effect.2 2 This mechanism was like “tachycardia-
dependent conduction disturbance”, AV block might
occur after increased vagal tone stopped, due to the rel-
atively prolonged AV nodal refractoriness.2 6 Fourth,
hemodynamic, hormonal, autonomic, and emotional
changes related to pregnancy might be associated with
arrhythmias.28,29
Body height has been considered an important
determinant of the dose of spinal anesthesia although
some evidence suggested no correlation between body
height or weight of parturients and spread of spinal
block.30,31 In our study, all parturients were given the
same dose of spinal anesthetic agent. There was no dif-
ference between age, body height, weight and spread
of the blockade. Thus, it is not necessary to vary the
dose of hyperbaric bupivacaine according to parturi-
ent’s age, body height or weight.
In summary, our study showed that the incidence
of arrhythmias as well as hypotension during spinal
anesthesia for Cesarean section was higher than we
expected. Although most of these arrhythmias were
transient and recovered spontaneously, they might
occur unexpectedly and, sometimes, require immedi-
ate treatment. It is necessary to remain vigilant and
careful monitoring of patients during spinal anesthesia
for Cesarean section is warranted, especially in older
parturients.
vagotonia and the site of the block is within the AV
node. The likelihood of the development of complete
AV block may be very low. Usually, Mobitz type II is
associated with a wide QRS complex and is due to dis-
ease of the His-Purkinje system.1 8It is more likely asso-
ciated with a high mortality rate and requires a
pacemaker to prevent more advanced AV block or car-
diac arrest. However, electrophysiologic studies in
Mobitz type II block with narrow QRS complexes
(absence of bundle-branch block) sometimes localized
the block at the AV node or proximal His-bun-
dle.13,19–21 Some studies demonstrated that vagal activi-
ty could modify AV conduction to produce first degree
to complete heart block including Mobitz type
II.13,20–25 For vagally mediated AV block, the decision
regarding the use of pacemakers is not based on the
type of block or on QRS duration but on the underly-
ing clinical settings and the correlation of symptoms.2 6
For all our patients with second degree AV block, the
prognosis was benign, because they had narrow QRS
complexes and only occurred transiently during spinal
anesthesia without significant ventricular pause.
There were 17 cases (6.7%) of severe bradycardia
during spinal anesthesia in our patients. There are no
studies of the relation between neonatal outcome and
maternal bradycardia during anesthesia. However,
maternal bradycardia might reduce uterine blood flow.
To protect both the fetus and the parturient, all of the
parturients with severe bradycardia received 0.5 - 1
mg atropine iv. One case suddenly developed severe
bradycardia and loss of consciousness without warning
Thus, we emphasize the importance of careful moni-
toring of patients and early management of side
effects. These may be the keys in preventing more
dangerous conditions, such as asystole.
References
There are many mechanisms to explain the high inci-
dence of intraoperative arrhythmias. First, the cephalic
spread of spinal block induced a relative increase in
parasympathetic activity by blockade of cardiac sympa-
thetic stimulation or vasovagal attack through decreased
venous return.6 The differences in latency and duration
of various cardiac tissues in response to this unstable
autonomic tone2 2 might encourage arrhythmias. Second,
nausea, vomiting and surgical manipulation during
Cesarean section might also increase vagal tone. The rel-
ative increase in parasympathetic activity was not associ-
ated only with hypotension, but also with bradycardia
and AV block in our study. Third, there were four cases
of second degree AV block occurring immediately after
intravenous ephedrine for hypotension or atropine for
bradycardia. Though AV nodal conduction was
enhanced and intranodal block tended to decrease after
1 Abboud TK, Dror A, Mosaad P, et al. Mini-dose
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