|Year : 2007 | Volume
| Issue : 4 | Page : 269
Preoperative assessment of cardiac risk
MD, Director Medical Services, Sr.Consultant & Chief, Anaesthesiology & Intensive Care, Rabindranath Tagore International Institute of Cardiac Sciences, 124, Mukundapur, Kolkata - 700099, India
|Date of Web Publication||20-Mar-2010|
Rabindranath Tagore International Institute of Cardiac Sciences, 124,Mukundapur, Kolkata - 700099
Source of Support: None, Conflict of Interest: None
Keywords: Preoperative, Cardiac risk
|How to cite this article:|
Rupert E. Preoperative assessment of cardiac risk. Indian J Anaesth 2007;51:269
| Introduction|| |
Annually around 100 million adults undergo non-cardiac surgery and the incidence of cardiac complications is between 0.5-1.0% which is the leading cause of perioperative morbidity and mortality  . The incidence of these complications is higher in patients undergoing vascular surgical procedures  . This increased risk of perioperative cardiac complications is due to both the patient characteristics and the specific surgical procedures.
Advances in anaesthetic and surgical techniques have improved perioperative outcome in recent years. There is a trend towards performing procedures in older and sicker patients, among whom the prevalence of or risk factors for cardiovascular disease is increasing. This tendency and the fear of perioperative cardiac complications prompt preoperative risk identification, stratification and modification of risk factors.
This article is an update on preoperative assessment of patients at risk of cardiac disease undergoing non-cardiac surgery.
| Goals|| |
- Identify patients at risk through history, physical examination and electrocardiogram (EKG).
- Evaluate the severity of underlying cardiac disease through cardiac testing taking care to minimize expenditure and to perform specialized tests only on high-risk patients. Testing low-risk patients increases costs and may cause harm by delaying a non-cardiac operation.
- Stratify the extent of risk and determine the need for preoperative interventions to minimize the risk of perioperative cardiac complications.
| Evaluation of cardiac risk|| |
The cornerstone of preoperative cardiac evaluation includes review of history [Table 1], physical examination [Table 2], diagnostic tests [Table 3], and knowledge of the planned surgical procedure. Preoperative resting electrocardiogram is readily available, inexpensive, easy to perform and able to interpret and detect previous myocardial infarction, acute ischaemia, or arrhythmias. The presence of abnormalities such as Q waves and non sinus rhythms has been shown to correlate with adverse postoperative cardiac events.
| Overview of cardiac risk indices|| |
A number of risk indices have been developed [Table 4]. The accuracy of each of these risk indices is controversial. A cardiac risk index to be useful, it has to be applicable to all and be consistently accurate.
ASA  - used for assessment of the patient's overall physical status and to predict morbidity and mortality.
NYHA/CCS  - used for risk stratification of medical patients with angina, but they have been adapted for use in surgical patients.
Cardiac Risk Index (CRI) - Goldman et al  identified 9 independent variables in a prospective study of 1001 patients undergoing noncardiac surgery that correlated with an increased risk of perioperative cardiac events. These variables were recent myocardial infarction, greater than 5 premature ventricular contractions per minute on a preoperative EKG, presence of jugular venous distension or a third heart sound, cardiac rhythm other than sinus, age greater than 70, emergency surgery, aortic stenosis, and intraperitoneal, intrathoracic, or aortic surgery. They developed a risk index score based on the presence of these factors.
Modified Cardiac Risk Index - Detsky et al  validated and further modified Goldman's cardiac risk index by giving the type of surgery a separate pretest probability. He modified the congestive heart failure (CHF) variables and included recent or previous myocardial infarction and severity of angina.
Cardiac Risk Index by Goldman and modification by Detsky were helpful in identifying risk factors for cardiac morbidity but were very cumbersome to apply. Furthermore, these indices performed less well when applied to vascular surgical candidates. ,.
Revised Cardiac Risk Index (RCRI) by Lee et al  in 1999 derived and prospectively validated a simplified risk index based on the original Goldman index. Their study identified 6 independent predictors of adverse cardiac outcome in patients undergoing noncardiac surgery.
- High-risk surgical procedure - defined as thoracic, abdominal, or pelvic vascular (e.g., aorta, renal, mesenteric) surgery.
- Ischaemic heart disease, defined as
History of myocardial infarction
History of or current angina
Use of sublingual nitroglycerin,
Positive exercise test
Q waves on ECG
Patients who have undergone PTCA or CABG and who have chest pain presumed to be of ischaemic origin
- Heart failure, defined as
Left ventricular failure by physical examination
History of paroxysmal nocturnal dyspnea
History of pulmonary edema
S 3 or bilateral rales on physical examination
Pulmonary edema on chest x-ray
- Cerebrovascular disease, defined as
History of transient ischaemic attack
History of cerebrovascular accident
- Insulin-dependent diabetes mellitus
- Chronic renal insufficiency, defined as
Baseline creatinine >2.0 mg.dL -1
The rates of major cardiac complications were found to be 0.5%, 1.3%, 4%, and 9% in patients with 0, 1, 2, or 3 or more of these risk factors, respectively. This revised cardiac risk index has been validated in number of studies.
| American College of Cardiology/American Heart Association (ACC/AHA) guidelines|| |
The standard of care in recent years is defined by American College of Cardiology/ American Heart Association (ACC/AHA) who have developed consensus guidelines for the preoperative cardiac evaluation. It was published in 1996 then updated in 2002 , to include additional data on beta-blockers, arrhythmias, and coronary evaluation and interventions. The ACC/AHA guidelines provide a framework for screening and identifying patients who are at high risk for perioperative cardiac events (PCE). History, physical examination and preoperative EKG form the basis for risk stratification. According to the AHA/ACC guidelines, risk for PCE depends on the patient's medical history, current functional status, and the specific surgical procedure. The guidelines stress that the indications for further testing and preoperative intervention are, in general, the same as in the nonoperative setting. For all cases this algorithmic approach should be used by anaesthesiologists, surgeons and internists for management
The ACC algorithm employs a strategy, using the urgency of surgery, history of previous coronary evaluation or treatment, clinical risk predictors, surgery-specific risk, and a patient's functional capacity.
Clinical predictors of perioperative cardiac events (PCE)
With respect to their medical history, the guidelines identify ''major,'' ''intermediate,'' and ''minor'' predictors of increased risk [Table 5].
| Functional capacity|| |
Exercise tolerance a determinant of perioperative risk is evaluated by the estimated energy requirement [Table 6] for various activities. The Duke Activity Status Index provides the physician with a set of questions to determine a patient's functional capacity. One MET represents the oxygen consumption of a resting adult (3.5 ml.kg -1 .min -1 ). A cutoff of 4 METS is used for decision making in the algorithm as perioperative cardiac risks are increased in patients unable to meet a 4-MET demand during most normal daily activities.
Functional capacity is defined as poor (<4 METS), moderate (4-7 METS), or good (>7-10 METS) based on evaluation of the patient's daily activity. Measurements on a treadmill inducing ischaemia at low-level exercise (<5 MET or heart rate <100 / min) identifies a high-risk group, whereas the achievement of more than 7 MET (or heart rate >130 / min) without ischaemia identifies a low-risk group. In the Revised cardiac risk index by Lee et al  functional status was not independently associated with risk. If patients reduce exertion because of cardiac symptoms but still meet a 4-MET threshold, clinicians will underestimate risk. Conversely, noncardiac functional limitations (e.g., knee or back pain) may falsely overestimate cardiac risk.
Surgery-specific risk factors
Surgery-specific cardiac risk [Table 7] is related to the type of surgery and the duration and intensity of perioperative physiological stress associated with the procedures.
One should also consider the risk of not operating on the patient while estimating the risk of surgery . It is unethical to refuse a procedure when their survival is threatened by the disease for example oncological or limb salvaging procedures, infections requiring surgery, or disabling orthopaedic procedures. The institutions infrastructure and overall perioperative care must also be taken into account, as it influences outcome of procedures. Risk reduction strategies include perioperative beta-blockade, staged procedures, limiting the extent of planned procedure, maintaining normothermia, avoiding anaemia and good postoperative analgesia.
| Algorithm (ACC/AHA) for stepwise approach on perioperative evaluation|| |
- This is an algorithm [Figure 1] proposed by ACC/AHA for decisions regarding the need for further evaluation.
- It is based on expert opinion and incorporates 8 steps. First evaluate urgency of surgery and appropriateness of formal preoperative assessment then determine whether patient has had previous revascularization or coronary evaluation.
- Unstable coronary syndromes are identified and appropriate treatment started i.e. delay or cancel surgery, medical management, coronary angiogram. Subsequent treatment is dictated by findings in angiogram.
- For intermediate and minor clinical predictors the decision for further testing depends on interaction of clinical risk factors, surgery specific risk and functional capacity.
- Stepwise approach to assessment of CAD in patients planned for noncardiac surgery is clinically effective and cost effective.
| Clinical situations which should alert the anaesthesiologist|| |
The following examples should potentially alert anaesthesiologists regarding need to evaluate and provide further testing.
- Patients with acute coronary syndromes, such as unstable angina or decompensated heart failure from ischaemia are at high risk of developing further decompensation, myocardial infarction, and death during the perioperative period. Such patients should not undergo noncardiac surgery.
- If surgery is emergent consider stabilization by pharmacologic and mechanical interventions and proceed for surgery without delay. Consider risk stratification in the postoperative period. Avoid further testing unless the results will impact perioperative management.
- Patients with critical aortic stenosis may be asymptomatic and evaluation of systolic ejection murmur is warranted. Patients with critical aortic stenosis may have a high risk of undergoing elective noncardiac surgery.
- Patients with dyspnea on mild exertion are at high risk of developing perioperative ventricular dysfunction, myocardial ischaemia and MI. Consider additional monitoring and testing as they have high probability of extensive CAD.
- Previous MI has shown an increased risk of reinfarction if the MI was within six months of surgery. With the advent of thrombolytic therapy and angioplasty this time interval may no longer be valid. The American Heart association and American College of Cardiology Task Force now advocates MI of less than six weeks as the group with the highest risk. Subsequent to this risk stratification is based on presentation of disease with patients with active ischaemia being at highest risk.
- Watch for peripheral vascular disease as they have a high association with CAD.
- Diabetes mellitus especially if long standing with evidence of end organ damage have a higher probability of silent MI and ischaemia. Diabetes is an independent risk factor for perioperative cardiac morbidity.
- Patients with hypertension and left ventricular hypertrophy undergoing noncardiac surgery have a higher perioperative risk.
| Tests to confirm cardiovascular disease|| |
Preoperative testing is aimed at answering questions raised by history and physical examination. No cardiovascular test should be performed if the results will not change perioperative management. No test exists that fully stratify all risks, because perioperative cardiac events are multifactorial  .
| Indications for preoperative cardiac testing|| |
- Patients with intermediate clinical predictors
- Prognostic assessment of patients undergoing initial evaluation for suspected or proven coronary artery disease (CAD).
- Evaluation of patients with change in clinical status
- Evaluation of adequacy of medical treatment
- Prognostic assessment after an acute coronary syndrome.
Noninvasive tests can be divided into resting tests, exercise tests and pharmacologic tests with myocardial perfusion imaging or echocardiography.
| Resting echocardiography|| |
Resting echocardiography is a simple and inexpensive form of cardiac imaging. The assessment of resting left ventricular function is not routinely recommended for preoperative screening. It is indicated for the detection of impaired left ventricular function and valvular heart disease. Impaired left ventricular function is no longer a predictor for short-term outcome due to improved perioperative care but remains a significant predictor for long-term adverse cardiac events. Echocardiogram does not reliably predict perioperative ischaemic events but it is of value in assessing valvular pathology. The presence and severity of aortic stenosis is associated with a fivefold increased risk of perioperative cardiac events  . Considering this, it is important to detect the presence and significance of valve disease.
| Information|| |
- Regional wall motion abnormalities
Type - hypokinesia, akinesia, dyskinesia
Location - anterior, septal, lateral, inferior, posterior
- Ejection fraction
- Chamber enlargements / hypertrophy
- Assessment of valve morphology and function
- Assessment of congenital and other diseases
| Stress tests|| |
Exercise stress test
Dobutamine stress echocardiography
Dipyridamole thallium scintigraphy
Stress tests are dynamic investigations, which demonstrate the ischaemic threshold, the maximal tolerated heart rate, the localization, and the amount of threatened myocardium. An interruption of the test before reaching the maximal heart rate identifies an increased risk of perioperative ischaemic events  . The positive and negative predictive value of all stress tests is in the range of 20-30% and 95-99% respectively as the incidence of perioperative cardiac complications is low (<10%) and more than 90% of patients have a straightforward perioperative course.
| Exercise stress testing|| |
Exercise stress testing is the first screening step in stress testing of ambulatory patients. It is a widely available and inexpensive method of screening.
| Physiology|| |
With exercise mean arterial pressure increases despite significant decreases in systemic vascular resistance due to marked increases in cardiac output as much as fourfold during maximal exercise. The increases in cardiac output are due to heart rate which can increase by upto 300% and stroke volume increase by upto 20%. The determinants of myocardial MVO2 that are affected by exercise are - heart rate, wall tension and contractility. This increase in oxygen consumption is met by increase in blood flow and minimally by increase in extraction. The increase in blood flow is achieved by marked vasodilation of coronary arterial bed in response to metabolic and other demands during exercise. Coronary vascular reserve plays an important role in ischaemic heart response to exercise. Impairment of reserve leads to myocardial ischaemia and its sequelae, arrhythmias and pump dysfunction  .
| Limitations and interpretation of ECG exercise tests|| |
- Only half of the patients achieve peak heart rates > 75% of their age-predicted maximum.
- A negative test in a patient who achieves the targeted heart rate-blood pressure product is usually associated with low risk for perioperative cardiac complications.
- Ischaemia induced by low-level exercise indicates high risk.
- Failure to reach the target heart rate makes the test inadequate for excluding myocardial ischaemia unless a normal workload is achieved despite the lower heart rate and such patients are at increased risk for perioperative complications based on their poor functional capacity.
- The test has a positive predictive value of 18% (range 5-81%) and a negative predictive value to be 97% (range 90-100%).
- Obtain and document details of exercise stress test rather than stating it was normal or abnormal.
- The peak heart rate, systolic blood pressure, and rate-pressure product (or double product)
- METS and percent of target heart rate achieved
- ECG changes, symptoms, or arrhythmias occurring during the test and at recovery phase.
- A patient with symptoms or ischaemia at a lower workload is at increased risk compared with a patient able to reach a higher metabolic (MET) threshold.
- The anaesthesiologist should be aware of patient's threshold heart rate, blood pressure and double product to help manage the patient's blood pressure and heart rate intraoperatively so that the double product remains below the ischaemic threshold.
Mechanism of action:
- Coronary artery vasodilatation, (dipyridamole or adenosine) and or
- Increased myocardial oxygen demand -(dobutamine).
The decision of which test to be used should be based on the expertise in one's institution, consideration of relative contraindications to dipyridamole or dobutamine.
Dipyridamole thallium scanning (DTS) Dipyridamole decreases adenosine uptake. Adenosine causes coronary vasodilatation preferentially distributing blood to normal coronaries and reducing blood flow distal to coronary stenosis. Myocardial imaging with thallium initially and after several hours demonstrates defects in myocardium at risk. Prior to testing, patients should avoid theophylline preparations and caffeine because of their antagonistic effect on dipyridamole. Side effects associated with the use of dipyridamole include bronchospasm, chest pain, headache, and dizziness; these symptoms often can be reversed by administration of IV aminophylline. Pooled data showed a positive predictive value of 16% (range 6-67%) and a negative predictive value of almost 99% (range 98-100%)
Dobutamine stress echocardiogram (DSE) - Dobutamine infusion increases heart rate and inotropy and echocardiography is performed at discrete points to detect new or worsened regional wall motion abnormalities (RWMA). Dobutamine stress echocardiogram has a positive predictive value of 15% (range 7-25%) and a negative predictive value of 99% (range 93-100%). The extent and severity of new or worsening RWMA, particularly at low ischaemic thresholds, is predictive of both short- and long-term outcome. Dobutamine testing should be avoided in patients with significant arrhythmias, marked hypertension or hypotension, and suspected critical aortic stenosis.
| Ambulatory ECG monitoring|| |
The positive predictive value for perioperative MI and death was approximately 10% with negative predictive value of 95%). The use of this test is limited.
[TAG:2]Risk reduction strategies [/TAG:2]
- Perioperative management
- Anaesthetic techniques
- General versus regional anaesthesia
- Temperature regulation
- Invasive monitoring - pulmonary artery catheter, transesophageal echocardiography for high risk surgical procedures
- Surgical approach
- Laparoscopic, endovascular procedures
- Beta blockers
- Other anti-ischaemic medications
Preoperative coronary revascularization / valvuloplasty
| Rationale for perioperative beta blocker therapy|| |
Numerous investigators have studied the role of various beta-blockers in different perioperative settings and have found a reduction in ischaemic events and death ,,,. There may even be a benefit of giving beta-blockers intraoperatively to patients who have not received them preoperatively.
Cardiovascular and other effects (anti-arrhythmic, anti-inflammatory, altered gene expression and receptor activity, protection against apoptosis) of â-blockers may account for their cardio-protective effect in the operative and non-operative setting. All â-blockers, except those with intrinsic sympathetic activity reduce mortality. Catecholamines increase each of the four determinants of myocardial oxygen consumption (i.e. heart rate, preload, afterload, and contractility). â-Blockers have the potential of reducing myocardial O2 consumption (thus improving the myocardial O 2 supply/demand balance) by decreasing sympathetic tone and myocardial contractility, in turn resulting in decreases in heart rate and arterial pressure  .
[TAG:2]Criteria for use of perioperative β blockers :[/TAG:2] 
Recommendations for preoperative coronary angiogram / coronary intervention: The decision for or against preoperative angiogram, coronary revascularization, percutaneous interventions (PCI) or coronary artery bypass grafting (CABG), should be based entirely on universally accepted medical indications for coronary revascularization and the appropriate technique. The philosophy of performing preoperative coronary revascularization merely 'to get the patient through surgery' is contrary to all available evidence. If the decision for preoperative coronary revascularization is made, timing with respect to the subsequent surgery appears crucial.
- Use if patients meet any two or more criteria -
Age > 65 years, Hypertension, Diabetes mellitus not requiring insulin, Current smokers, Serum cholesterol > 240mg.dl -1 (6.2 mmol.L -1 )
- Use if patients meet any one of revised cardiac risk index criteria 
Coronary stenting: If a coronary stent is placed, elective non-cardiac surgery should be delayed for an absolute minimum of 2 weeks, but ideally for 4-6 weeks for bare metal stents and six months for drug eluting stents as this delay will allow completion of a course of dual antiplatelet medication and allow bare metal stents to be endothelialized. If patients require elective non-cardiac surgery within 2 months of PCI, there are several options. If surgery (and the surgeon)allows dual antiplatelet therapy (mostly clopidogrel and aspirin) to be continued perioperatively, a drug-eluting stent can be placed. If surgery (or the surgeon) does not allow perioperative continuation of dual antiplatelet therapy, a drug-eluting stent should probably not be used. Survivors of PCI face the perioperative risk of coronary (stent) thrombosis or hemorrhage associated with discontinuation or continuation of dual antiplatelet therapy, respectively.
Preoperative surgical coronary revascularization: The indications for CABG before noncardiac surgery remain the same as in the non operative setting. Timing is crucial if major non-cardiac surgery is indicated following recent CABG. Available data is limited and suggests postponing elective major noncardiac surgery for at least 4-6 weeks, possibly for even up to 6 months after CABG. In patients who survive CABG the risk of subsequent noncardiac surgery is low. CABG significantly improves survival in patients with peripheral vascular disease and triple vessel coronary disease especially with depressed ventricular function ,.
| Conclusion|| |
Preoperative assessment of cardiac risk in patients undergoing non cardiac surgery is a challenge to the anaesthesiologist. A thorough history, physical examination, judicious use of tests is usually sufficient to assess patients and categorize them into a low-risk, intermediate-risk and high-risk for surgery. It is important to combine preoperative assessment of cardiac risk with perioperative cardiac risk reduction strategies and optimization of medical treatment to improve patients' long term cardiac outcome. The therapeutic strategies may differ according to the situation: medical treatment may be optimized, surgical procedure and anaesthetic management modified, or the risk/benefit ratio of a surgical procedure evaluated differently.[Table 8]
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]