INTERVENTIONAL CARDIOLOGY
Interventional cardiology procedures include coronary angiography
and cardiac catheterization, coronary artery angioplasty/stenting, valvotomy, closure
of intracardiac defects, electrophysiologic studies with pathway ablation, and cardioversion.
These procedures, both diagnostic and therapeutic, can benefit from the involvement
of anesthesia personnel in terms of both procedural outcome and patient comfort.
Anesthesiologists caring for these patients must be familiar with the patient's
medical condition, as well as the planned procedure, to develop a coherent anesthetic
plan.
The environment of the cardiac catheterization laboratory is not
optimized for anesthetic management. The rooms are frequently darkened to allow
better visualization of fluoroscopic images, and they are crowded with equipment
and personnel. Radiation safety is as much a concern in the cardiac catheterization
laboratory as it is in other areas where x-ray devices are used. Thus, personnel
in these rooms must wear heavy and bulky lead aprons and thyroid shields, and the
rooms are further crowded by the presence of mobile leaded glass radiation shields.
It is critical that the requirements for anesthetic equipment and monitoring discussed
earlier be met and that the anesthesiologist remain vigilant for rapid changes in
the patient's condition, which frequently occur in this distracting environment.
Coronary Angiography
The coronary vasculature may be visualized with the use of radiographic
contrast media to allow identification of coronary anatomy, precise determination
of the presence and location of coronary artery stenoses, and detection of coronary
vasospasm.[78]
Recently, the American College of
Cardiology and the American Heart Association updated their guidelines for the practice
of coronary angiography.[79]
Although other procedures,
such as rapid CT and MRI, may allow determination of the presence of coronary artery
disease, coronary angiography remains the "gold standard" for this diagnosis. In
addition, interventional procedures to improve coronary blood flow may be performed
as part of the same procedure.[80]
Some patients
undergoing diagnostic procedures may be inpatients, but many are outpatients, and
the anesthetic plan must take this possibility into account. It is at present controversial
whether interventional procedures should be performed in the outpatient setting.
Coronary angiography and cardiac catheterization carry a less
than 2% risk of significant complications.[79]
Risks include complications pertaining to vascular access, such as hemorrhage, infection,
or ischemia; cardiac ischemia in patients with coronary artery disease; catheter-related
complications such as coronary dissection and thromboembolic events (including stroke);
and contrast-related reactions. The risk of significant complications is increased
in patients with cardiogenic shock, acute myocardial infarction, unstable angina,
renal failure, cardiomyopathy, valvular heart disease, congestive heart failure,
hypertension, or inpatient hospital status.[79]
[81]
Very ill, unstable patients considered at
high
risk of requiring cardiac surgery should be transferred to institutions with cardiac
surgical backup available.[79]
Coronary angiography is performed by passing a catheter in retrograde
fashion through the arterial tree to the aortic root for the selective injection
of contrast media into the ostia of the coronary arteries. Usually, the catheter
has been inserted through the femoral artery, but arterial occlusive disease may
necessitate access via the brachial
or radial arteries. Increasingly, access is electively gained through the radial
artery, with improvement in patient satisfaction and decreased cost.[82]
[83]
Local anesthesia is used at the catheter insertion
site to limit patient discomfort related to vascular access. Peripheral intravenous
access is necessary for the administration of cardiac medications and sedative/analgesics.
The usual anesthesia management is by sedation/analgesia, with general anesthesia
reserved for sedation failure, uncooperative patients, or those who require airway
control to manage respiratory failure. Anesthetic agents used commonly include fentanyl
and midazolam, sometimes supplemented with propofol. Sedation and analgesia are
helpful in reducing the discomfort associated with contrast injection and remaining
motionless and supine during long procedures. Sublingual and intravenous nitroglycerin
should be readily available for administration if myocardial ischemia develops, and
emergency resuscitation drugs and equipment must be immediately accessible. Supplemental
oxygen is administered, typically by nasal cannula, and standard ASA monitors are
used. Arterial blood pressure can be directly transduced from the arterial introducer,
and noninvasive blood pressure can be monitored as well. The ECG tracing must be
scrutinized and the patient closely watched for the presence of angina or heart failure,
all while anesthetic personnel are shielded from exposure to radiation. Heparin
is frequently administered, even for diagnostic catheterization, and the effects
are often reversed with protamine. Typical heparin doses range from 2500 to 5000
IU intravenously. For interventional procedures, higher heparin doses (i.e., 10,000
IU intravenously) are given, with a target ACT of over 300 seconds. Patients must
be monitored carefully after protamine administration to detect the predictable peripheral
vasodilation, as well as less predictable anaphylactic and anaphylactoid reactions
or the rare catastrophic pulmonary vasoconstrictive crisis associated with protamine
administration. Care must also be taken to carefully monitor the patient for reaction
to the contrast medium. Finally, the patient must be observed closely after the
procedure for bleeding or hematoma at the catheter site, as well as for ischemia
of the limb distal to the site. Recovery should take place in a fully equipped and
staffed recovery area, with the patient discharged only after meeting standard discharge
criteria.
Platelet aggregation inhibitors and low-molecular-weight heparin
are increasingly commonly being administered during interventional cardiac catheterization
and have resulted in improved outcomes despite the reduction in heparin dose.[84]
Platelet aggregation inhibitors used have included abciximab, ticlopidine, and clopidogrel.
Numerous studies have shown the benefits of antiplatelet therapy in both acute and
chronic coronary syndromes.[85]
[86]
[87]
[88]
A notable
side effect of abciximab is elevation of the ACT independent of heparin.[89]
Coronary artery disease is assessed by detection of stenoses after
injection of contrast medium selectively into each main coronary artery. Stenoses
greater than 50% to 70% of the normal arterial diameter are considered hemodynamically
significant, although lesser stenoses may be clinically important. Coronary artery
disease is classified as one-, two-, or three-vessel disease or left main coronary
disease. An additional cause of myocardial ischemia is coronary arterial spasm.
When the patient has typical symptoms without significant atherosclerotic disease
at cardiac catheterization, coronary vasospasm should be investigated. Provocative
agents, including ergonovine maleate, methylergonovine maleate, or intracoronary
acetylcholine, may be given to provoke spasm while contrast medium is injected into
the coronary artery. Intracoronary vasodilators such as nitroglycerin may be required
when provocative agents are administered. Intracoronary diltiazem may be used to
treat resistant vasospasm.[90]
[91]
 |
