Cardiac Conduction Disturbances
Bradyarrhythmias, especially if profound or associated with dizziness
or syncope, are generally managed with pacemakers. However, on rare occasion, chronic
bifascicular block (right bundle branch block with a left anterior or posterior hemiblock
or a left bundle branch block with combined left anterior and posterior hemiblocks),
even when only a first-degree heart block is present, progresses to complete heart
block and sudden perioperative death. Such progression is rare, however. In six
studies, less than 2% of the approximately 266 patients with bifascicular block progressed
to complete heart block perioperatively.[484]
[485]
[486]
[487]
[488]
[489]
On
Figure 27-19
Summary of the normal acoustic characteristics of valve
prostheses according to type and location. A2
, aortic second sound; AC,
aortic valve closure sound; AO, aortic valve opening sound; DM, diastolic murmur;
MC, mitral valve closure sound; MO, mitral valve opening sound; P2
, pulmonary
second sound; S1
, first heart sound; S2
, second heart sound;
SEM, systolic ejection murmur. (Redrawn from Smith ND, Raizada V, Abrams
J: Auscultation of the normally functioning prosthetic valve. Ann Intern Med 95:594,
1981.)
the other hand, these patients have a high 5-year mortality rate (160 of 554 patients,
or 29%). Most of the deaths were related to tachyarrhythmias or MI—events
not usually preventable by traditional pacemakers.[490]
Thus, the presence of a bifascicular block on ECG should make the anesthesiologist
more worried about associated coronary artery disease or left ventricular dysfunction.
Nevertheless, these patients rarely have complete heart block perioperatively.
Therefore, prophylactic preoperative insertion of temporary pacing wires for bifascicular
block does not seem warranted. However, a central route can be established in advance
in the event that a temporary pacemaker needs to be inserted (most operating rooms
do not rely on transthoracic pacing, although such might be attempted if available).
[491]
The actual pacemaker equipment and appropriate
personnel should be immediately available and tested regularly because symptomatic
heart block does occur perioperatively in more than 1% of patients.[484]
[485]
[486]
[487]
[488]
One study appears to have confirmed this
rate
of at least 1% for patients undergoing cardiac surgery.[492]
One percent of patients who had no preoperative insertion of a pacing pulmonary
artery catheter subsequently required pacing before cardiopulmonary bypass. By contrast,
19% of patients who had such a catheter in place underwent cardiac pacing before
cardiopulmonary bypass. Predictors of the need for pacing included previous symptomatic
bradyarrhythmia, a history of transient complete AV block, and aortic valve disease.
More than five PVCs per minute on preoperative examination correlate
with perioperative cardiac morbidity.[367]
[375]
[376]
[390]
To
the
classic criteria for treating PVCs
(the presence of R-on-T couplets, the occurrence of more than three PVCs per minute,
and multifocality of PVCs) must be added frequent (>10/hr over a 24-hour period)
and repetitive ventricular beats. Electrophysiologic and programmed ventricular
stimulation studies are being used to indicate and guide treatment for patients with
ischemic heart disease or recurrent arrhythmias and for survivors of out-of-hospital
cardiac arrest.[493]
Although such patients are
often treated with antiarrhythmic therapy, attention to their underlying condition
should be a focus of our preoperative management. Chronic antiarrhythmic therapy
is discussed in the last section of this chapter. Torsades de pointes is an arrhythmia
characterized by episodes of alternating electrical polarity such that the major
vector of the QRS complex seems to alternate around an isoelectric line. The hallmark
enabling differential diagnosis from ventricular tachycardia is the unusual response
of this arrhythmia to commonly used antiarrhythmic drugs. That is, the use of drugs
that prolong the QT interval (e.g., quinidine, procainamide, disopyramide, some of
the antihistamines, and the antipsychotic phenothiazines) may well make the arrhythmia
more frequent or of longer duration. Reports of the sudden occurrence of torsades
de pointes during surgery have been rare in the anesthesia literature. Immediate
therapy consists of the administration of magnesium or electrical cardioversion,
followed by overdrive cardiac pacing or the administration of β-adrenergic agonists
and discontinuation of drugs that prolong the QT interval.
Premature atrial contractions and cardiac rhythm other than sinus
also correlate with perioperative cardiac morbidity.[367]
[375]
These arrhythmias may be more a marker of
poor cardiovascular reserve than a specific cause of perioperative cardiac complications.
Pre-excitation syndrome is the name for supraventricular tachycardias
associated with AV bypass tracts.[494]
Successful
treatment, which is predicated on an understanding of the clinical and electrophysiologic
manifestations of the syndrome, consists of either catheter ablation techniques[490]
or surgery using preoperative and intraoperative techniques that avoid release of
sympathetic substances and other vasoactive substances and therefore tachyarrhythmias.
[495]
[496]
[497]
Anesthesia for electrophysiologic procedures is discussed in Chapter
50
and Chapter 68
).
Pacemakers (Control of Arrhythmias)
The types of pacemakers available and the indications for their
use have changed significantly since 1980. More than
*N,
NSAPE; B, BPEG; G, generic.
90% of pacemakers are inserted for the treatment of bradyarrhythmias occurring either
after tachycardia (bradytachy syndrome) or by themselves (i.e., in sick sinus syndrome
or AV conduction disorders). Physiologic pacing is an attempt to increase the patient's
hemodynamic response to increased metabolic demands. An increase in heart rate provides
greater augmentation of cardiac output than maintenance of AV synchrony does. The
rate of pacemaker insertion has also declined by more than 50% since 1980; in 1984
a publication by the American College of Cardiology and the American Heart Association
of indications for pacemaker insertion codified these changes in practice patterns.
The most common pacemaker for this type of dysfunction is the ventricular R-wave-inhibited
(demand) type (VVI) (letter codes are described later and in Table
27-40
). More complex pacemakers are presently being used to provide better
cardiac output in stressful situations and decrease myocardial wall stress[498]
or to treat ventricular or supraventricular tachyarrhythmias. Lithium batteries
now give a pacemaker a 5- to 10-year life span. Programmable pacemakers are adjustable
for sensitivity and rate. Currently available atrial pacemakers fired by an outside
radiofrequency source permit termination of reentrant or pre-excitation atrial arrhythmias;
similarly, ventricular pacemakers can be used to terminate supraventricular tachycardia
and recurrent ventricular tachycardia.[499]
Thus,
in addition to learning about the patient's underlying disease, current condition,
and drug therapy, the anesthesiologist must learn, preoperatively, the following
information about any implanted pacemaker[499]
:
- The indication for placement of the pacemaker and the default rhythm (i.e.,
what rhythm occurs if the pacemaker does not capture).
- The type of pacemaker (demand, fixed, or radiofrequency), the chamber paced,
and the chamber sensed. Pacemakers have traditionally been given a five-letter code
(see Table 27-40
). However,
most pacemakers implanted since 1980 have codes consisting of only the first three
letters. The first letter indicates the chamber
paced (i.e., V = ventricle, A = atrium, D = dual or both). The second
letter indicates the chamber sensed (i.e., V = ventricle, A = atrium, D = dual, O
= none). The third letter indicates the sensing
pattern (i.e., O = no sensing, fixed mode; I = inhibited, demand pacer; T = triggered,
meaning that the sensing of an electrical impulse triggers a pacemaker spike; D =
dual, i.e., both T and I). For example, a VOO pacemaker paces the ventricle, does
not sense, and is in a fixed mode.
In other words, it is a fixed-rate ventricular pacemaker. A VVI pacemaker paces
the ventricle, senses the ventricle, and is inhibited. It is a ventricular-inhibited
demand pacemaker. A DVI pacemaker paces both the atrium and ventricle, senses only
the ventricle, and is inhibited. Thus, it is a sequential AV demand pacemaker that
fires when it does not sense intrinsic ventricular activity. Rate-modulated pacemakers
increase the heart rate in response to increased demand. They have special sensors
and are placed in patients who may have abnormal sinus node function. These pacemakers
have an R in the fourth position of the pacemaker letter code[498]
(e.g., VVIR; see Table 27-40
).
A DDDCP pacemaker has multiprogrammable "physiologic" dual-chamber pacing with telemetry
and antitachyarrhythmia-pacing capability. An OOOPS is a simple, programmable cardioverter,
defibrillator, or cardioverter-defibrillator. It cannot be overemphasized that no
generic code can describe every antiarrhythmic device in a comprehensive and unambiguous
fashion. It seems to us that it is beneficial to consult with an electrophysiologist/cardiologist
before anesthetizing any patient who has a pacemaker.
- How to detect deterioration in battery function (increased rate or decreased
rate).
- How to change the mode or fire the pacemaker if it is of the radiofrequency
type. (These procedures should not only be learned by anesthesiologists but also
be demonstrated to them. In addition, the magnet or programming device [or both]
should be in or near the operating room at the time of surgery.)
- The current rate and sensitivity settings of the pacemaker.
- Whether the pacemaker is currently functioning and how well.
Because demand pacemakers can sense electrocautery, which sometimes
inhibits pacemaker firing, asystole can occur in a pacemaker-dependent patient.
A review of the causes of interference has recently been published.[500]
Most pacemakers can be converted to a fixed rate, and the anesthesiologist can take
the following precautions: (1) have the cardiologist demonstrate how such conversion
is done and (2) have the necessary magnet or programming device, or both, available
in the operating room. In addition, the ground plate should be as far from the pulse
generator and lead as possible, a bipolar form of electrocautery should be used,
and if possible, some measure of blood flow should be monitored (i.e., Doppler detector,
pulse oximetry unaffected by electrocautery, or intra-arterial line). The rationale
for the last measure is that electrocautery temporarily affects the accuracy of ECG
results; because asystole could occur during this period, a measure of blood flow
is necessary. Currently, at least eight manufacturers produce a total of more than
80 types of pacemakers, with a variety of default programs. A default program is
the secondary program (i.e., the generator circuit) to which the primary program
will revert if it senses problems in the initial circuit. Because default programs
differ, pacemaker malfunction will be manifested differently depending on the brand
and model. Thus, it is necessary to learn before surgery how problems will be manifested
with each pacemaker during surgery.[499]
The most common cause of temporary pacemaker malfunction is lack
of contact between the electrode wire and the endocardium. Pacemaker spikes continue
to exist on the ECG oscilloscope, even when no myocardial contractions propel blood.
This situation has occurred with muscular exertion, blunt trauma, cardioversion,
and positive-pressure ventilation.[501]
Treatment
consists of advancing the electrode until it captures, administering isoproterenol
(if that worked in the past), external pacing, or failing that, cardiopulmonary resuscitation.
During the preoperative examination, the anesthesiologist can
also assess progression of underlying disease (e.g., CHF, electrolyte disorders,
and the condition of all systems related to the underlying disease). Antiarrhythmic
therapy and its implications are discussed in the last section of this chapter.
