Medications:
Simvastatin 20 mg oral daily
ACE-I
Heparin drip—started as inpatient
Nitroglycerin drip—started as inpatient
Aspirin 81 mg oral daily—started as inpatient
Allergies:
Nil Known
Past Medical History:
Cardiac:
Hypertension
Hypercholesterolemia
Physical Exam:
Vital Signs:
BP 125/81 HR 80 RR 16 Oxygen saturation: 98%
Coronary Angiogram:
80% stenosis of the Proximal Left Anterior Descending Artery(LAD)
90% stenosis of the Right Coronary Artery (RCA)
70% stenosis of the Left Circumflex Artery (LCx)
Right dominant circulation
LV gram suggests a diminished ejection fraction
Transthoracic Echocardiogram summary report:
Normal thickness of left ventricular wall
Normal size left ventricle
Diminished left ventricular ejection fraction—estimated 35–40%
Hypokinesis in the inferior wall and anterior, anterolateral and anteroseptal walls
Normal appearance and function of the right ventricle
Trace to mild tricuspid regurgitation. Otherwise normal valves
No pericardial effusion
- 1.
What are the indications for non-emergent CABG?
The AHA/ACC guidelines indicate the level of evidence for CABG surgery. The following are considered Class 1 indications for surgery in stable CAD [1]:
CABG to improve survival is recommended for patients with significant (>50% diameter stenosis) left main coronary artery disease. (Level of Evidence: B)
CABG to improve survival is beneficial in patients with significant (>70% diameter) stenosis in 3 main coronary arteries (with or without involvement of the proximal LAD artery) or in the proximal LAD plus 1 other major coronary artery. (Level of Evidence: B)
Other indications for CABG or PCI include improving survival in patients who survive sudden cardiac death with presumed ischemia mediated VT, or to improve symptoms in patients with persistent angina despite goal-directed medical therapy. Both of these indications relate to a significant (>70% diameter) stenosis in a major coronary artery.
CABG is also recommended in patients undergoing non-coronary cardiac surgery with greater than or equal to 50% luminal diameter narrowing of the left main coronary artery or greater than or equal to 70% luminal narrowing of other major coronary arteries. (Level of Evidence: C)
The indications for emergency CABG are different to those for the elective situation.
- 2.
What are the important features to note on the coronary angiogram?
The coronary angiogram will demonstrate the location and severity of coronary artery disease and will often also have a left ventriculogram. This gives an assessment of LV function and the degree of MR, if present. The degree of coronary disease may guide the conduct of anesthesia and whether an Intra Aortic Balloon Pump (IABP) will be required.
Patients undergoing CABG usually have significant involvement of the LAD and multi-vessel disease not amenable to PCI. Anatomical considerations include:
Where is the disease and what is the extent of the disease?
Is there left main stenosis? (>50% stenosis of the left main)
Is there left main equivalent stenosis (>70% stenosis of the proximal LAD and LCx)
Are any vessels completely occluded? (These will be supplied by collaterals and are more pressure dependent)
Coronary anatomy from angiography that should raise concern for the induction of anesthesia include the following:
Severe left main (>90%) or left main equivalent disease
Chronic obstruction of 2 vessels (e.g., RCA and LAD. This results in the majority of myocardium being supplied by the remaining vessel, in this scenario the LCx)
Also, if the patient is having active rest angina or ECG changes despite maximal medical management, regardless of anatomy, this is obviously of concern.
- 3.
What scoring systems are used for determining the predicted risk of mortality (PROM)?
Several scoring systems exist and are all based on large databases of patients having undergone cardiac surgery. These scores utilize a variety of preoperative factors (such as age, LV function, renal dysfunction, etc.), to estimate a patient’s 30-day PROM.
These have better predictive power for lower risk patients:
EuroSCORE
European System for Cardiac Operative Risk Evaluation. First published in 1999, and predominantly a score for CABG alone [2].
EuroSCORE II
Updated EuroSCORE in 2012. Based on a much larger database of contemporary surgical outcomes.
STS score
Society of Thoracic Surgeons. Provides PROM for CABG, valve, or combined CABG/valve procedures [3].
- 4.
What factors may significantly increase the risk of cardiac surgery?
The following are some factors which may increase the risk of cardiac surgery:
Age
Co-morbidities
LV dysfunction, renal dysfunction, pulmonary hypertension, hepatic dysfunction, active endocarditis
Frailty (difficult to measure)
The American College of Surgeons suggests use of the Fried or Robinson scales [4]
Urgency status
Active ischemia/failure, preoperative inotropes/mechanical support (VAD/IABP)
Technical factors
Redo cardiac surgery, poor coronary targets (i.e., difficult to graft/incomplete revascularization), aortic calcification (difficult to cannulate/cross clamp).
- 5.
What are generally accepted rates of complications for elective CABG in a patient with normal LV function?
Mortality | 1–2% |
Stroke | 1–2% |
Perioperative MI | 2–5% |
Early graft dysfunction | 1–5% |
Deep sternal wound infection | 1% (up to 3% if bilateral IMA) |
Transfusion of RBC | 20–50% |
Renal failure requiring dialysis | 1–2% |
Prolonged ventilation | 1–5% |
These may increase with age, LV impairment, urgent status, previous neurological event, renal impairment, and airways disease.
- 6.
How long should antiplatelet/anticoagulants be withheld prior to surgery?
This depends on both the urgency of the operation and the pharmacology of the drug involved.
Aspirin (irreversible platelet inhibitor—blocks platelet cyclo-oxygenase):
Can safely continue low dose aspirin (81 mg daily; this is an AHA class I recommendation.
Clopidogrel (irreversible thienopyridine platelet inhibitor—blocks ADP):
Should wait 5 days, but can operate if necessary, accepting a higher risk of bleeding.
Prasugrel (more potent irreversible thienopyridine than clopidogrel):
Should wait 7 days and should not operate unless absolutely required in the first 3 days.
Ticagralor (potent reversible thienopyridine):
Ideally should wait 5 days, but can operate if necessary with higher risk of bleeding.
Abciximab—reversible platelet inhibitor—(monoclonal antibody against GPIIb/IIIa):
Is often used in PCI and in unstable angina with critical coronary anatomy.
Plasma half-life of 30 min with significant platelet dysfunction for 48 h.
Stopping the drug 12 h prior to surgery will limit blood loss with surgery.
Unfractionated Heparin (UFH):
It produces its major anticoagulant effect by inactivating thrombin and activated factor X (factor Xa) through an antithrombin III-dependent mechanism; half-life is 1–2 h.
Is usually ceased 6 h prior to surgery unless the patient is suffering from unstable angina/acute coronary syndrome, in which case it can be continued to the OR.
Low Molecular Weight Heparins (LMWH):
Much longer half-life and dosing depends on renal function.
If on therapeutic LMWH, ideally should wait 24 h from the previous dose, longer if abnormal renal function.
The patient should ideally be switched to UFH 48 h prior to surgery.
Bivalirudin:
A reversible direct thrombin inhibitor with a half-life of 25 min. Should be stopped 6 h prior to surgery.
Coumadin (warfarin):
Cease 5 days prior and bridge with LMWH or UFH depending on the clinical requirement for anticoagulation.
Novel oral anticoagulants (NOACs):
These include the direct thrombin inhibitor dabigatran (Pradaxa®) and the Xa inhibitors rivaroxoban (Xarelto®) and apixiban (Eliquis®).
These have a shorter effective half-life than Coumadin but should be stopped at least 4 days prior to cardiac surgery and bridged with LMWH/UFH as required.
- 7.
Should this patient have investigation of the carotid arteries performed?
The AHA recommends carotid artery duplex in a patient with the following high risk features (Class IIa recommendation. Level of Evidence: C) [5]:
>65 years of age
Left main coronary stenosis
Peripheral arterial disease
History of cerebrovascular disease (stroke/TIA)
Hypertension
Smoking
Diabetes mellitus
The key findings are internal carotid artery (ICA) stenosis and vertebral artery flow. This will guide perfusion management on cardiopulmonary bypass (CPB), whether cerebral oximetry monitoring may be required intraoperatively, and whether concomitant carotid intervention is warranted.
- 8.
When is intervention for carotid artery disease indicated in the setting of CABG?
Concomitant carotid intervention (either pre-CABG, during, or post-CABG) is suggested for:
ICA stenosis 50–99% with a history of stroke or TIA (Class IIa)
Bilateral ICA stenosis 70–99% if asymptomatic (Class IIb)
Unilateral ICA stenosis 70–99% with contralateral occlusion (Class IIb).
All of these recommendations have a Level of Evidence: C
The ideal timing of concomitant carotid intervention is unclear from the evidence. Preoperative carotid intervention carries a higher perioperative MI risk, postoperative carries a higher stroke risk for the CABG, and carotid/CABG in the same setting carries a higher risk of stroke [6].
- 9.
Are all patients presenting for an isolated CABG procedure required to have a TTE performed prior to surgery?
Most patients in the modern era have had a TTE performed preoperatively. A select group may be able to proceed to CABG without a TTE:
If clinical exam shows no evidence of valvular disease, and
If the left heart catheterization showed normal LV function, and
No MR on LV gram, and
If they will have a TEE intraoperatively.
The important things to note on a preoperative TTE include the following:
LV function and size
RV function and size
Valvular pathology
Pulmonary pressures (estimated from the TR jet velocity)
Presence of a pericardial effusion
Aortic dimensions (looking for aneurysm).
- 10.
When is a myocardial viability test indicated in the preoperative work-up for planned CABG surgery?
The aim of CABG is for both a survival benefit and to reduce the symptoms of debilitating and refractory angina. Patients with significant myocardial scar will not see these benefits, as revascularization will not improve the scarred territory. Furthermore patients with anatomical three vessel disease with a large LAD territory scar are not considered to have clinical LAD disease and these patients may not see the survival benefit of CABG over PCI.
There are 4 states of ventricular myocardium [7]:
- (1)
Normal contractility—viable
- (2)
Hibernating—reversible ischemic hypocontractility with hypoperfusion
- (3)
Stunned—transient post-ischemic hypocontractility with normal perfusion
- (4)
Scar
Viability testing is utilized to determine what is viable myocardium and would be expected to benefit from revascularization. These studies include the following:
MRI:
Late gadolinium enhancement >50% of the LV wall thickness indicates nonviability.
Nuclear imaging:
Technetium sestamibi or Thallium. The radioisotopes are taken up by viable myocardium.
PET:
Viable myocardium will have FDG (fluorodeoxyglucose) uptake.
Stress echocardiography:
With exercise or dobutamine (to 20 mcg/kg/min)
Viable territories should improve with dobutamine [8].
- 11.
What conduits are available for bypasses and what factors influence the decision to use a particular conduit?
The most common conduits used for CABG include: the internal mammary arteries (left and right, referred to as LIMA and RIMA), the long saphenous vein, and the radial arteries. Other less commonly used vessels include the short saphenous vein, the right gastroepiploic artery, and the cephalic vein in the forearm.
Long-term patency of the grafts depends on the quality of the conduit as well as the quality of the target vessel. The LIMA has proven to be the most durable conduit with a 10-year patency of 95% when grafted to the LAD. A LIMA to the LAD is associated with improved survival compared with vein to the LAD, PCI, or medical therapy alone.
Saphenous vein grafts are immediately available, are not prone to spasm, and are not prone to competition with the native flow as opposed to arterial conduits (IMA and radial artery). However, the saphenous vein generally develops a thickened intima with associated obstructive disease as the vein becomes ‘arterialized.’ The 10-year patency of vein grafts to the RCA or LCX is approximately 70%.
The radial artery is particularly prone to spasm due to its thick and muscular media. Spasm is reduced by using topical and intra-luminal vasodilators (verapamil, nitroglycerin) and by grafting it to a coronary artery that has a high grade stenosis so that the native flow does not “compete” with the radial artery.
The nondominant arm is usually used and there should be clear communication preoperatively between the anesthesia and surgical teams so that a radial arterial line is not inserted into the artery that is to be harvested.
The risks of radial artery harvest include: hand ischemia (if the deep and superficial palmar arches are incomplete), and paresthesia from injury to the superficial radial nerve (on the lateral aspect of the dorsum of the hand). Postoperative hand weakness is uncommon.
An Allen’s test is performed to test whether the ulnar artery can adequately supply the hand by way of intact palmar arches.
- 12.
What is the evidence for an Allen’s Test?
Although there is little evidence that it is a particularly predictive test, it is commonly performed in the preoperative assessment [9].
- 13.
Should CABG be performed “on-pump” or “off-pump”? What are some of the supposed benefits of avoiding CPB?
On-pump CABG is the most common method of performing CABG in the USA. This refers to performing the bypasses with the heart arrested using cardiopulmonary bypass. This enables accurate visualization and performance of the coronary anastomosis in a still and bloodless field. However, this comes at the cost of the effects of CPB with possible neurological injury, renal injury, anemia, platelet dysfunction, and systemic inflammatory response.
Off-pump CABG (OPCAB) entails performing the bypasses on a beating heart without the use of CPB and is technically more difficult. There has been a lot of controversy regarding the benefits of either technique and there has been a resurgence of on-pump CABG in the USA. Two large randomized trials (ROOBY and CORONARY) failed to show a benefit of off-pump over on-pump at one year in terms of mortality, stroke or renal failure [10, 11].
In the ROOBY trial, off-pump was also found to be associated with significantly worse graft patency at one year.
- 14.
What are some of the issues faced by the anesthetist associated with performing OPCAB?
Issues include the following:
Thermoregulation (usually managed with assistance of the heart-lung machine)
The need for scrupulous management of hemodynamics by the anesthesiologist throughout the procedure
Changes in the utility and appearance of monitoring (ECG, TEE) during portions of the procedure
Management of ischemia during performance of the anastomoses
Manipulation of the heart rapidly alters loading conditions, which may also lead to arrhythmias and large swings in hemodynamics [12]
An awareness of the surgical requirements at various stages of the operation, when regional ischemia may be induced, and the cardiac manipulations performed are all required. Subsequently communication with the surgical team is even more critical than with conventional CABG.
- 15.
The patient says he is concerned about the anesthesia as his father had a CABG in his seventies and didn’t seem “quite right” for some time after. What would you tell him?
Neurological injury is one the most feared complications responsible for morbidity and mortality after cardiac surgery. It exists on a spectrum from definitive cerebrovascular accident (stroke) to subtle neurocognitive effects [13].
Stroke
There is a strong association between the burden of atherosclerotic disease and neurocognitive morbidity. If a patient is found to have high grade of atherosclerosis, or mobile plaque in the ascending aorta, then the operative technique may be altered in the hope of minimizing plaque mobilization.
Postoperative Cognitive Dysfunction (POCD)
Subtle neurocognitive dysfunction has been recognized to occur after cardiac surgery. Potential etiological factors have included CPB itself, inflammatory processes and embolic complications. More recent research suggests the degree of POCD after 3 months is unrelated to the type of surgery [14]. This is supported by the findings that the incidence of POCD is no different between OPCAB and conventional CABG [15].Related posts:
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