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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.51 no.6 Campinas Dec. 2001
Preoperative assessment and preparation of coronary artery disease patients for surgery*
Evaluación y preparo pré-operatorio del portador de enfermedad de las arterias coronarias
Gilson Ramos, M.D.I; José Ramos Filho, M.D.II; Edísio Pereira, M.D.III
IMestre em Ciências da Saúde;
Doutorando da Faculdade de Ciências da Saúde da UnB/DF; Especialista
em Clínica Médica; Co-responsável pelo Serviço de Anestesia
do Hospital Samaritano de Goiânia
IIDoutor em Medicina pela Universidade de Zurique/USP; Professor Titular e Responsável pela Disciplina de Cardiologia do Curso de Medicina da Universidade São Francisco, Bragança Paulista, SP
IIIPhD; Professor Doutor do Curso de Pós-Graduação da Faculdade de Ciências da Saúde da UnB - DF
BACKGROUND AND OBJECTIVES: Coronary artery
disease (CAD) patients are at greater perioperative morbidity and mortality
risk during non-cardiac surgery. Specific laboratory tests are important adjuncts
to clinical tests and should be one of the tools for evaluating and preparing
those patients. This review aims at establishing preoperative procedures to
minimize peri and postoperative morbidity and mortality in CAD patients.
CONTENTS: Characteristics of stable and unstable chest anginas are presented, along with clinical and functional classification criteria, diagnosis, clinical-surgical therapy and major cardiologic laboratory tests. In addition, types of angina are correlated to clinical procedures in order to propose a preoperative algorithm.
CONCLUSIONS: All CAD patients being considered for non-cardiac surgery should be carefully evaluated. Patients at high-risk require effective clinical control. For clinically stable patients, in the intermediate-risk group, functional non-invasive tests are recommended. The use of beta-blockers should be considered for all coronary patients.
Key Words: DISEASE, Cardiac: coronary disease; PREANESTHETIC EVALUATION
JUSTIFICATIVA Y OBJETIVOS: Portadores
de enfermedad arterial coronaria (EAC) presentan mayor morbi-mortalidad peri-operatoria
en cirugías no-cardíacas. Exámenes laboratoriales específicos
son aliados importantes del examen clínico y deben ser incluidos en el
arsenal propedéutico para evaluación y preparo de esos pacientes.
El objetivo de la presente revisión es establecer conductas pré-operatorias
para minimizar la morbi-mortalidad peri y pós-operatoria de los portadores
CONTENIDO: Son presentadas características de las anginas de pecho estable e inestable, criterios de clasificación clínica y funcional, diagnóstico, terapéutica clínica-quirúrgica y los principales test laboratoriales cardiológicos disponibles. Además, son correlacionados el tipo de angina con el procedimiento quirúrgico para propuesta de un algoritmo pré-operatorio.
CONCLUSIONES: Todos los portadores de EAC candidatos a cirugía no-cardíaca deben ser rigorosamente evaluados. Los identificados como de alto riesgo necesitan control clínico eficaz. En los candidatos clínicamente estables, considerados de riesgo intermediario, test funcionales no-invasivos son recomendables. En todos los coronariopatas el uso de b-bloqueador debe ser considerado.
Coronary failure or disease is the unbalance between myocardial oxygen supply and demand and may cause ischemia and heart cell necrosis. Coronary changes are major causes of cardiomyopathies and death among adults and are responsible for approximately 40% of all deaths of individuals above 60 years of age. Common etiology is arteriosclerosis, the incidence of which increases with age. In males, it evolves very rapidly between 30 and 50 years of age, time when it starts to more gradually progress and reaches its peak at 60 or 65 years of age. In females, atheromatosis onset is late and coincides with menopause. In individuals below 40 years of age, damages are more localized and affect one artery. In elderly, however, damages are in general diffuse and may affect many branches. Coronary disease patients submitted to surgeries are not an infrequent event. It is estimated that 12% of patients submitted to non-cardiac surgery present or are at risk for coronary disease1,2. Undesirable events, fatal or not, depend on location, number of vessels affected and the degree of obstructive injuries and of the functional importance of the affected vessel. Those patients are at increased risk for peri and postoperative morbidity and mortality and should be evaluated and prepared by a multidisciplinary team, including the anesthesiologist, whose participation is paramount for a successful procedure.
Clinical diagnosis is often based on ECG, the most important findings of which are changes in the ST segment3. However, a normal ECG is frequently seen in patients with chronic artery disease. Subsequent lab tests aim at: a) explaining situations with inconclusive results; b) functionally classifying chronic artery disease patients; and c) defining therapeutic goals.
Coronary patients are classified according to clinical and functional characteristics. The clinical classification establishes two groups: stable and unstable chronic angina. The latter has several clinical variances (recent angina, rapidly progressive angina, subentrying angina, intermediate syndrome and post recent infarction angina). Stable chronic angina is characterized by retro-sternal pain episodes in grasp, triggered by physical or emotional stress. Pain lasts from two to ten minutes and disappears with rest or sublingual nitrates. Unstable angina is a clinical status with imminent risk for acute myocardial infarction. Crises may occur at rest or minimum efforts, seem to be related to coronary artery tone and do not disappear with normal therapy. Prinzmetal angina is in general considered a separate disease. It is rare and in general severe with 2/3 of patients presenting significant proximal coronary injuries4. So Prinzmetal patients should be treated as unstable angina patients. The functional classification relates to physical activities coronary patients are entitled to perform. Patients may belong to functional classes I, II, III or IV (Chart I), according to their functional capacity5,6. This variable is estimated in metabolic equivalents (METs) where 1 MET is equivalent to the consumption of 3.5 ml O2.kg-1.min-1 or the consumption of a 70 kg person at rest and in the supine position (Chart II). Functional capacity is considered excellent if higher than 7 METs, moderate if between 4 and 7 METs and poor when lower than 4 METs7,8.
The initial treatment is clinical with nitrates, beta-blockers and calcium channel blockers. Anti platelet aggregation drugs should be administered to all angina patients. Once the diagnosis is determined, chronic artery disease patients should be immediately treated and those with unstable angina or stable angina functional class III or IV should be referred to cinecoronariography9. Patients with stable angina functional class I or II must have their functional capacity confirmed. Ergonometric tests are excellent for such end10. Those with poor functional capacity should be further evaluated by cinecoronariography7-9. On the other hand, chronic artery disease patients, with moderate or excellent functional capacity, do not need additional evaluations; just follow up and clinical therapy7,8.
Cinecoronariography locates and defines coronary injuries, in addition to determining the therapeutic approach. Coronary angioplasty (with or without stent) is indicated for obstructive injuries with stenosis of the vessel's lumen diameter higher than 70% (flow limiting injuries), especially those of types A and B1. These obstructive injuries are small (< 10 mm), concentric, easily accessible, with non angulated segments, smooth contours, few or no calcification and lack of ostial injury. Injuries B2 and C are more complex, eccentric and tortuous11. Even so, they may today be corrected by angioplasty (stent) performed by an experienced surgeon although with a higher procedure-related risk. Flow limiting injuries in a coronary branch is an absolute indication for surgical myocardial revascularization. Similarly, coronary ostium injuries are also indications for revascularization surgeries, although in special situations and with experienced professionals angioplasty may be attempted, especially in emergency situations11. Flow limiting multiartery injuries justify a thorough clinical discussion with the participation of the hemodynamics specialist and the cardiac surgeon, due to the possibility of only being corrected by myocardial revascularization.
PREOPERATIVE EVALUATION AND PREPARATION
The surgical risk of non cardiac surgeries is classified in high, intermediate and low risk, according to the possibility of death and non fatal myocardial infarction. If the incidence of such events is above 5%, surgeries are considered of high risk; if between 1% and 5%, they are considered of moderate risk; and if below 1% they are considered of low risk (Chart III)7,8.
The incidence of acute myocardial infarction (AMI) after non cardiac surgeries in the non cardiac population varies from 0.1% to 0.2%. This incidence significantly increases among coronary artery disease patients and varies from 2% to 17%12. Half of the ischemic events occur on the day of the surgery, but the incidence peak is seen on the third day1,2. Perioperative mortality is also higher in cardiac patients. On the other hand, those submitted to previous successful revascularization have a postoperative mortality equivalent to individuals without coronary disease13. Surgery and anesthesia cause a circulatory overload to which the ill heart is more exposed than the healthy heart14. So, a careful clinical evaluation, supported by additional preoperative tests, is a major foundation for an accurate evaluation and may decrease surgical morbi-mortality of cardiac patients, thus assuring the success of the procedure.
The preoperative evaluation of clinically stable coronary disease patients scheduled for non cardiac surgery consists initially of a detailed clinical exam and conventional ECG, which allow for determining associated co-morbidity, stratifying the surgical risk, adopting different approaches and intervening, when necessary, before the non cardiac surgery.
The additional preoperative investigation of cardiac patients is based on the clinical form of their disease and on the type of surgical procedure they will be submitted to. So, patients with unstable or stable functional class III or IV angina, recent myocardial infarction (up to one month) or those with evidences of residual ischemia are considered at high risk (Chart IV) and should be evaluated by cinecoronariography and possible angioplasty or myocardial revascularization before the non cardiac surgery7,8. On the other hand, patients with stable angina functional class I or II are at intermediate risk and should be classified according to their functional capacity. It is worth mentioning that in some situations it is not possible to clinically evaluate the functional capacity. In those cases, it should be determined by a stress test, which in some cases may be impossible to apply. So, another non-invasive test should be considered to estimate preoperative risk and management.
Low functional capacity has been considered a predictive factor for surgical risk in non cardiac surgeries. So, patients at intermediate risk with low functional capacity should be submitted to other non-invasive cardiologic tests before being sent to surgery, regardless of the type of surgery7,8. Similarly, those with moderate or excellent functional capacity and scheduled for high risk procedures should be submitted to the same tests to classify the risk. Such tests, however, are unnecessary if the surgery is of low or intermediate risk. When non-invasive tests reveal patients at high surgical risk, cinecoronariography should be considered7,8. When the same tests reveal low or moderate risk, patients should be sent to surgery. Chart V summarizes in an algorhythm a proposal to preoperatively evaluate coronary disease patients.
As to drug treatment, there are no doubts that the surgical stress promotes an increase in catecholamines, which may cause adverse cardiac effects. So, patients are more vulnerable to arrhythmias and arteriosclerotic plate rupture. That is why perioperative beta-blockers have been proposed in non cardiac surgeries for chronic artery disease patients. Those agents decrease the incidence of ischemia and myocardial infarction, not only in the perioperative period, but also in the long run. Based on those evidences, b-antagonists should be routinely used in the perioperative period of cardiac patients except when counterindicated15.
NON-INVASIVE AND SEMI-INVASIVE CARDIOLOGIC TESTS
Most common non-invasive cardiologic tests are bidimensional echocardiography, ergonometric test, stress echocardiography with dobutamine, myocardial scintigraphy with dipyridamole and holter. Transesophageal doppler echo-cardiography is a semi-invasive method very useful to evaluate coronary patients.
Bidimensional echocardiography - the echocardiography lab allows for the division of the left ventricle in several segments (11, 13 or 16) and for the evaluation of global and regional functions, end systolic volume and ejection fraction. In the vast majority of coronary disease patients, it is possible to determine changes in segmental contractility16. The best way to detect myocardial ischemia is through the abnormal movement of the ischemic segment (decrease of segmental systolic inspissator in the region of the affected wall). The involvement of up to two segments should be analyzed together with ventricular and functional capacity. On the other hand, changes in three or more segments in different regions characterize a patient at high surgical risk. If there is no segmental contractility changes but there is a clinical suspicion of myocardial ischemia, patient should be submitted to ergometric test or stress echocardiography. End systolic volume is of paramount importance to evaluate ejection efficiency of the left ventricle and is the major determinant of survivors after myocardial infarction. End systolic volume lower than or equal to 34 ml.m2 correlates to a lower death rate. Ejection fraction lower than 50% with high end systolic volume is a predictive factor for future cardiac events17,18.
Ergometric test - evaluates cardiovascular overload imposed by physical exercise and functional capacity. It does not consider, however, the effects of psychological stress which affects factors determining myocardial oxygen consumption. The ergometric test applied to chronic multiartery disease patients is approximately 90% sensitive19. Patients with functional capacity below 4 METs and low physical activity level-induced myocardial ischemia (ST segment under-unlevelled) are at high peri and postoperative risk. On the other hand, ischemic patients with functional capacity above 7 METs are considered at low cardiac risk10.
Stress echocardiography with dobutamine - very useful method to evaluate patients with diseases (neurological, orthopedic, etc.) which prevent the ergometric test. Followed by transthoracic echocardiography at rest, the stress echocardiography with dobutamine may induce myocardial ischemia and has shown to be better than the sub-maximal ergometric test to diagnose multiartery disease patients20,21. A low butamine dose (5 µg.kg-1.min-1) may detect feasible ischemic muscle and myocardial involvement. When the technical quality of the transthoracic stress echocar- diography is limited, the transesophageal method with stress may replace it, giving important information about patients with triartery involvement22. The normal test has a negative predictive value of 93% to 100% and segmental contraction abnormalities have a positive predictive value of 7% to 50% and may be considered as risk factors for peri and postoperative cardiac events23. Abnormal contractions in three or more segments of ischemics different regions indicate patients at high risk for peri or postoperative cardiac events.
Myocardial scyntigraphy with dipyridamole - thalium or sestamibi scintigraphy with pharmacological stress induced by dipyridamole may show the existence of reversible or non reversible ischemias (previous infarction) with high sensitivity (93%) although the low specificity of the method (62%). A fixed ischemia in 1 or 2 segments should be evaluated together with the ventricular function. However, 3 or more ischemic segments characterize high risk patients. Some authors have shown defects of thalium redistribution and perioperative ischemia. Low specificity and high cost limit its use24.
Holter - the long duration electrocardiography may detect transient ischemic episodes characterized by ST segment under-unlevelling in severe cardiac patients who never referred angina pain even during a myocardial infarction4. This method may be useful, especially in diabetes type 2 patients who have a higher incidence of silent ischemic events; however, there are many false-positive results in normal individuals25. There are certain limitations of the method for patients with abnormal ECG at rest. Per se, this exam is not enough to refer patients to cinecoronariography.
Transesophageal doppler echocardiography - this semi-invasive method is very useful to evaluate blood flow velocity in coronary circulation and coronary reserve flow (CRF) in the anterior descending aorta and the coronary sinus. The baseline flow velocity is obtained during maximum hyperemia induced by venous adenosine for 4 minutes. CAD patients with moderate functional capacity and scheduled for high risk surgeries should be submitted to transesophageal echocardiography. When CRF is higher than 2, severe coronary injuries may be ruled out, and when lower than 2, obstructive injuries are considered significant and patients are at high risk26,27. Some countries adopt this method as a perioperative routine for high risk surgeries. This monitoring explains in a sensitive and continuous way, global and segmental functions of the left ventricle without interfering with the surgical field. Using this method one may obtain the perioperative etiology of an acute hypotension or the onset of a left ventricular myocardial ischemia before electro- cardiographic changes are seen, faster, safer and more reliable way than when using pulmonar artery catheterization28,29.
All chronic artery disease patients scheduled for non cardiac surgeries must be carefully evaluated. Those at high risk need a strict clinical control. Elective procedures should be postponed in adverse clinical situations where patients are not compensated. For clinically stable patients (most of them functional class I or II) and considered of moderate risk, non-invasive functional tests are recommended. b-blockers should be considered for all coronary disease patients.
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Correspondence to Submitted for publication February 14, 2001 * Received
from Disciplina de Cardiologia do Curso de Medicina da Universidade São
Francisco, Bragança Paulista, SP
Dr. Gilson Ramos
Address: Rua 8, 74/402 Setor Oeste
ZIP: 74115-100 City: Goiânia, Brazil
Accepted for publication April 27, 2001
Submitted for publication February 14, 2001
* Received from Disciplina de Cardiologia do Curso de Medicina da Universidade São Francisco, Bragança Paulista, SP