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Preoperative investigations in adult cardiac surgery patients
CARDIOTHORACIC SURGERY I
Preoperative investigations in adult cardiac surgery patients
Radionuclide perfusion imaging with thallium or technetium can also be used as a screening investigation for significant coronary artery disease. For patients that are unable to exercise, vasodilators such as adenosine may be used to stress the heart. Images are obtained at peak stress and at rest. Reversible perfusion defects indicate viable ischaemic myocardium; irreversible defects indicate non-viable scar.
Olivia Swingland Kunal Bhakhri
Cardiac catheterization: a recent (within the previous 12 months) coronary angiogram is required for patients undergoing coronary artery bypass surgery. It is used to demonstrate coronary artery anatomy and to identify the location and severity of disease; a stenosis >50% is considered significant. This guides selection of the target vessels to graft. A left ventriculogram shows left ventricular function and may detect mitral regurgitation.
Jon Anderson
Abstract Preoperative investigations in cardiac surgery can be divided into diagnostic and assessment of fitness for surgery. Diagnostic investigations are used to detect and evaluate coronary, valvular, myocardial and thoracic aortic disease. Knowledge of an individual patient’s comorbidities is essential in determining the risk of postoperative morbidity and mortality, thus allowing for more accurate informed consent. Furthermore, the results of preoperative investigations may predict the likely postoperative hospital stay and support required in order to maximize the chances of uneventful recovery. Additionally, the changing operative demographic, with an increased age and burden of co-morbidities frequently makes open-heart surgery challenging prompting a reliance on minimally invasive procedures that may not require cardiopulmonary bypass such as transcatheter aortic valve implantation (TAVI) and mitral valve repair. This article highlights the tests for preoperative diagnosis and assessment of fitness for surgery in adult cardiac patients. They should be used to guide clinicians in making appropriate management decisions, particularly with regard to elderly, frail or complex cardiac cases discussed in the setting of joint cardiology and cardiothoracic meetings.
Stress echocardiography: echocardiography provides information on ejection fraction, left ventricular size and regional wall motion abnormalities. Stress echocardiograms are performed using dobutamine infusion to pharmacologically stress the heart by increasing cardiac work. It can identify hibernating myocardium and predicts the likely improvement in cardiac performance following revascularization. (Hibernating myocardium is defined as reversible left ventricular dysfunction caused by chronically insufficient myocardial perfusion.) Positron emission tomography (PET) scanning helps to differentiate stunned and hibernating myocardium from scarred myocardium in patients who do not complain of angina but present primarily with symptoms of heart failure or poor left ventricular function. FDG-PET additionally enables visualization of the metabolic activity in viable myocardial cells.
Keywords Cardiac; carotid; echocardiogram; investigations; preoperative; risk stratification
Cardiac MRI can be used to further assess left ventricular function, myocardial perfusion and viability. Gadolinium contrast MRI discriminates between partial thickness and full thickness infarcts, and therefore is useful when evaluating patients with poor left ventricular function who are doubtful candidates for coronary revascularization.
Diagnostic investigations of adult cardiac disease Coronary heart disease The exercise tolerance test is a useful screening investigation in which a patient undergoes a standardized protocol of increasing exercise with continuous recording of 12-lead ECG and blood pressure monitoring. It is used for the diagnosis of ischaemic heart disease (ST segment depression >1 mm, fall in blood pressure or angina), and the assessment of asymptomatic valvular disease and exercise related arrhythmias. Its usefulness is limited in patients on beta-blockers, those with limited exercise tolerance due to co-morbidities and those with resting ECG abnormalities.
Coronary CT angiogram (CTA): advances in CT imaging technology, including the introduction of multidetector (multi-slice) row systems with electrocardiographic gating, have made imaging of the heart and the coronary arteries feasible. Cardiac CTA can provide information about coronary anatomy and left ventricular function that can be used in the evaluation of patients with suspected or known CAD. It is also useful to visualize previous coronary grafts in patients planned for redo cardiac surgery. In most circumstances, a negative coronary CT angiogram rules out significant obstructive coronary disease with a very high degree of confidence, based on negative predictive value of 93% obtained in cohorts. Therefore it is useful for managing patients scheduled for non-coronary artery cardiac surgery particularly in the surgery of aortic root aneurysms where it may be difficult to engage the coronary ostia in angiography. On the contrary, the positive predictive values probabilities following a positive coronary CT angiogram are more variable,
Olivia Swingland MBBChir MSc is a Clinical Fellow at the Royal Free Hospital, London, UK. Conflicts of interest: none declared. Kunal Bhakhri MRCS is a Cardiothoracic Registrar at The Hammersmith Hospital, London, UK. Conflicts of interest: none declared. Jon Anderson FRCS is a Cardiothoracic Consultant at the Hammersmith Hospital, London, UK. Conflicts of interest: none declared.
SURGERY 33:2
52
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
techniques already described, particularly echocardiography, cardiac MRI and cardiac catheterization.
due in part to the tendency to overestimate disease severity, particularly in smaller and more distal coronary segments or in segments with artefacts caused by calcification in the arterial walls. It can therefore be used concomitantly with myocardial perfusion imaging (MPI). The differences in the parameters measured by MPI (‘function’ or ‘physiology’) and CTA (‘anatomy’) must be considered when making patient management decisions with these studies. Of note, a normal MPI does not exclude the presence of coronary atherosclerosis although it does signify a very low risk of future major adverse events over the short to intermediate term. Conversely, coronary CTA allows detection of some coronary atherosclerotic plaques that are not haemodynamically significant. Neither test can presently identify with any reasonable clinical probability non obstructive coronary plaques that might rupture in the future and cause acute myocardial infarction.
Disease of the thoracic aorta Chest radiograph may show mediastinal widening suggesting an aortic aneurysm. It detects pleural effusions, and a large cardiac silhouette may indicate pericardial effusion. CT aortogram is a valuable investigation for the diagnosis and assessment of thoracic aortic disease, demonstrating aortic atheroma, calcification, ulceration, intramural haematoma, dissection and aneurysm. It is widely available in UK hospitals and is therefore the first-line investigation in the acute setting. Multi-slice CT scanning with three-dimensional reconstruction is essential for preoperative planning for non-emergency thoracic aortic interventions (both surgical and endovascular) and for postoperative evaluation.
Valvular heart disease Echocardiography Transthoracic echocardiogram (TTE) e is the primary investigation for valvular heart disease. It detects most valvular conditions and is widely available in UK hospitals, but the quality of images obtained is operator and machine dependent. Transoesophageal echocardiography (TOE) e provides excellent images of the heart, allowing more detailed examination of the mitral valve and aortic root. It is vital in patients with mitral regurgitation who may be suitable for mitral valve repair. Limitations include the need for sedation or anaesthesia and the availability of a skilled operator to conduct the procedure and interpret the images. Three-dimensional echocardiography e can be performed via a trans-thoracic and trans-oesophageal approach. It can provide a surgeon’s view allowing morphologic evaluation of the valve leaflets especially of the prolapsing segment and measurement of the annulus, thus helping plan surgical strategy. It use as an accurate predictor of surgical closure has been well documented. It also allows a dynamic assessment of the valve following surgical repair, for example the ability to look at the mitral closure line in a loaded ventricle in systole. Four-dimensional echocardiography e is used to provide real-time rendering of the heart based on 3-D reconstructed images.
MRI is the investigation of choice for the screening of chronic thoracic aortic dissection or aneurysm. It avoids the radiation dose of CT and provides excellent images of the aortic tree as well as allowing dynamic assessment of valves and ventricles. It can illustrate subclinical disease using molecular imaging techniques. For example quantifying the proportion of elastin in the aortic wall, therefore identifying patients at risk of aortic dilatation that require follow up and intervention. Additionally, it can demonstrate areas of irregular endothelial permeability thus enabling focused preventative treatment. Moreover, fourdimensional phase contrast MRI scanning (4D PC-MR) provides imaging of the flow in both the true and the false lumens, enabling calculation of the rate of aortic expansion, hence guiding prospective endovascular treatment. Positron emission tomography (PET) is increasingly used with CT. This has the benefit of significantly superior images when performed in combination. It can illustrate aortic wall inflammation, with preliminary studies showing strong correlation between increasing inflammation and worsening outcomes. Echocardiography enables rapid assessment of the aortic valve, root and ascending aorta. It is useful to confirm the presence of a dissection flap and to examine the aortic valve in acute type A dissection. Although views of the arch are limited, echocardiography can also be used to screen for coarctation in patients with bicuspid aortic valve disease.
Cardiac catheterization Coronary angiography e is only performed in patients aged >40 years and in younger patients with significant risk factors for coronary artery disease. Aortography e can help to identify the severity of aortic regurgitation and the presence of aortic root or ascending aortic dilatation. Right-heart catheterization e is useful in patients with mitral or tricuspid valve disease, congenital heart disease, pulmonary hypertension and severe left ventricular dysfunction.
Preoperative assessment of fitness for surgery Risk stratification models: objective assessment of surgical risk is undertaken to facilitate better informed consent. Surgical risk is influenced by co-morbidity: diabetes chronic pulmonary disease renal dysfunction neurological dysfunction peripheral vascular disease endocrine disease obesity or frailty.
Structural disease of the heart Non-valvular heart disease such as atrial or ventricular septal defects, more complex adult congenital heart disease, pericardial fluid or thickening can be identified and evaluated using
SURGERY 33:2
53
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
The effect of risk factors on surgical outcome has been defined by risk stratification models The EuroSCORE I and II were developed using data from 128 European cardiac surgical centres. They remain the most commonly used scoring algorithm in Europe, incorporating 17 risk factors analysed as both additive and logistic scores. The original EuroSCORE I was criticised for over-estimating the risk of mortality; however, following a database update in 2011 EuroSCORE II was published. This is not only used for preoperative risk calculation but also for risk-adjusted evaluation of the postoperative mortality using Cumulative Sum Control Chart (CUSUM) analysis. This reflects the improving surgical outcomes associated with preoperative screening, surgical techniques and intensive care advances. EuroSCORE has comparable predictive value in both North America and Europe. The Bayes Model is the preferred method of risk stratification recommended by the Society for Cardiothoracic Surgery in Great Britain and Ireland (SCTS). Variations of the model exist, differing in the number of factors used to calculate the final risk score. The Bayes model requires more complex computer calculations of risks scores but more accurately reflects the target population.
History-taking and examination: specific questions and examinations relevant to cardiac surgery are listed in Table 1. Full blood count: unexplained anaemia (haematocrit <35%) is investigated and referred to a haematologist or gastroenterologist if appropriate. Stable patients may commence iron supplements or erythropoietin therapy preoperatively. A high white cell count (>11,000 per mm3) suggests underlying infection and should be investigated before elective surgery. Extensive research has illustrated significantly worse postoperative outcomes (mortality, length of hospital stay) when surgery was performed in the presence of intercurrent infection and raised CRP. A platelet count <100,000 per mm3 can indicate idiopathic thrombocytopenia or thrombotic abnormalities and should be referred to a haematologist. Coagulation: prothrombin time activated partial thromboplastin time and platelet count should be measured preoperatively. Abnormalities can be corrected using vitamin K, fresh frozen plasma and platelet transfusions if necessary. Patients on warfarin or heparin should have INR and APTT checked, respectively. Warfarin should be stopped 5 days before surgery if possible.
Preadmission clerking and investigations: the trend towards preadmission clinics is now well established. Generally led by junior doctors and nurse specialists, these sessions are valuable because: Patients and relatives can be familiarized with the hospital environment as they are invited to tour the wards and the intensive care unit. Preoperative tests can be streamlined and results are available well in advance of the scheduled surgery so abnormalities can be corrected or investigated before admission. These can then be discussed in multi-disciplinary meetings, an approach proven to improve both early and long-term outcomes. Patients have ample opportunity to ask further questions regarding their disease and the proposed surgery, thereby reinforcing informed consent.
Urea and electrolytes: hypokalaemia is a common abnormality seen in patients on diuretics and may cause premature ventricular ectopics, ventricular tachycardia and ventricular fibrillation. Raised creatinine (>120 mmol/l) indicates pre-existing renal impairment. Creatinine clearance can be calculated from the Cockcroft-Gault equation (Box 1). Patients with GFR <60 ml/min are at risk of developing postoperative renal failure requiring temporary or permanent haemodialysis. Biomarkers: the addition of specific biomarkers to preoperative investigations remains centre specific. The exception being Troponin T and I as an indicator of ongoing compromise to cardiac perfusion. Raised preoperative Troponin levels have been linked to prolonged ICU stay, increase in adverse outcomes including mortality.
History-taking and examination relevant to cardiac surgery History
Coronary risk factors
Examination
Medical history Surgical history Cardiovascular
Conduits for CABG Peripheral vascular disease BMI Dental hygiene
Smoking, hypertension, diabetes, hypercholesterolaemia, family history, socioeconomic status Respiratory, neurological, peripheral vascular, renal, hypothyroidism, PUD Including previous cardiac surgery Heart murmur in patients for CABG mandates echocardiogram Heart failure (beneficial to off-load prior to elective surgery) Carotid bruits Varicose veins/surgery Allen’s test to assess radial artery Relative contraindication to intra-aortic balloon pump Height and weight: Obesity and frailty increase risk Dental check essential for patients with heart valve disease
Table 1
SURGERY 33:2
54
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
The Cockcroft-Gault equation for calculating creatinine clearance Creatinine clearance ðmenÞ ¼
ð140 ageÞ weight ðkgÞ ðin women 0:85Þ 72 serum creatinine ðmg=100 mlÞ
Box 1
Variations in levels from the physiological norm of brain natriuretic peptide, vitamin D and growth differentiation factor 15 have also been linked with increased adverse events postoperatively. Monitoring these biomarkers may become more widespread as the demographic requiring surgery changes. Meticillin-resistant Staphylococcus aureus (MRSA) screening has been introduced on all patients preoperatively to help reduce the incidence of MRSA infection. Patients with positive swab results are given suppression therapy to reduce the risk of self-infection. Better hygiene and precautions taken by staff helps to prevent cross-contamination.
arrhythmias during surgery, with relevant medications being continued until surgery. A chest radiograph is an essential preoperative investigation to exclude coexisting lung disease (e.g. chronic obstructive pulmonary disease, lung fibrosis and carcinoma). Pulmonary function tests are routinely undertaken; however, they are of increased importance in patients who are heavy smokers or have chronic obstructive pulmonary disease or asthma. Baseline preoperative tests include bedside spirometry, pulse oximetry and arterial blood gas analysis. Patients with FEV1 <50% of predicted should have laboratory pulmonary function tests and referral to a respiratory physician. FEV1 <65% of vital capacity or FEV1 <1.5 e2.0 l predicts prolonged ventilator wean postoperatively.
12-lead ECG is always done as a baseline. It may reveal arrhythmia, conduction defect, myocardial infarction and ventricular hypertrophy. Preoperative control of heart rate prevents
Figure 1
SURGERY 33:2
55
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
Summary
Carotid Doppler is done in patients with: history of cerebrovascular accident or transient ischaemic attack carotid bruits peripheral vascular disease. The optimal surgical approach for coexistent significant carotid stenosis and coronary artery disease remains a contentious issue and is best determined on an individual patient basis. The essential role of multidisciplinary team meetings with combined cardiology and cardiothoracic team presence for discussing complex patient’s diagnoses, management and prognosis is usually carried out after some investigations have been performed. The role of these meetings has been proven to improve both short and long term patient outcomes.
SURGERY 33:2
Figure 1 illustrates the pathway taken by candidates for cardiac surgery. A FURTHER READING Cohn LH. Cardiac surgery in the adult. 4th edn. New York: McGraw-Hill, 2011. Swanton RH, Banerjee S. Swanton’s cardiology: a concise guide to clinical practice. 6th edn. Oxford: Blackwell Science, 2008.
WEBSITES http://www.scts.org/sections/audit/Cardiac/index.html. http://www.ctsnet.org/doc/2692. http://www.euroscore.org.
56
Ó 2014 Published by Elsevier Ltd.
Preoperative investigations in adult cardiac surgery patients
Radionuclide perfusion imaging with thallium or technetium can also be used as a screening investigation for significant coronary artery disease. For patients that are unable to exercise, vasodilators such as adenosine may be used to stress the heart. Images are obtained at peak stress and at rest. Reversible perfusion defects indicate viable ischaemic myocardium; irreversible defects indicate non-viable scar.
Olivia Swingland Kunal Bhakhri
Cardiac catheterization: a recent (within the previous 12 months) coronary angiogram is required for patients undergoing coronary artery bypass surgery. It is used to demonstrate coronary artery anatomy and to identify the location and severity of disease; a stenosis >50% is considered significant. This guides selection of the target vessels to graft. A left ventriculogram shows left ventricular function and may detect mitral regurgitation.
Jon Anderson
Abstract Preoperative investigations in cardiac surgery can be divided into diagnostic and assessment of fitness for surgery. Diagnostic investigations are used to detect and evaluate coronary, valvular, myocardial and thoracic aortic disease. Knowledge of an individual patient’s comorbidities is essential in determining the risk of postoperative morbidity and mortality, thus allowing for more accurate informed consent. Furthermore, the results of preoperative investigations may predict the likely postoperative hospital stay and support required in order to maximize the chances of uneventful recovery. Additionally, the changing operative demographic, with an increased age and burden of co-morbidities frequently makes open-heart surgery challenging prompting a reliance on minimally invasive procedures that may not require cardiopulmonary bypass such as transcatheter aortic valve implantation (TAVI) and mitral valve repair. This article highlights the tests for preoperative diagnosis and assessment of fitness for surgery in adult cardiac patients. They should be used to guide clinicians in making appropriate management decisions, particularly with regard to elderly, frail or complex cardiac cases discussed in the setting of joint cardiology and cardiothoracic meetings.
Stress echocardiography: echocardiography provides information on ejection fraction, left ventricular size and regional wall motion abnormalities. Stress echocardiograms are performed using dobutamine infusion to pharmacologically stress the heart by increasing cardiac work. It can identify hibernating myocardium and predicts the likely improvement in cardiac performance following revascularization. (Hibernating myocardium is defined as reversible left ventricular dysfunction caused by chronically insufficient myocardial perfusion.) Positron emission tomography (PET) scanning helps to differentiate stunned and hibernating myocardium from scarred myocardium in patients who do not complain of angina but present primarily with symptoms of heart failure or poor left ventricular function. FDG-PET additionally enables visualization of the metabolic activity in viable myocardial cells.
Keywords Cardiac; carotid; echocardiogram; investigations; preoperative; risk stratification
Cardiac MRI can be used to further assess left ventricular function, myocardial perfusion and viability. Gadolinium contrast MRI discriminates between partial thickness and full thickness infarcts, and therefore is useful when evaluating patients with poor left ventricular function who are doubtful candidates for coronary revascularization.
Diagnostic investigations of adult cardiac disease Coronary heart disease The exercise tolerance test is a useful screening investigation in which a patient undergoes a standardized protocol of increasing exercise with continuous recording of 12-lead ECG and blood pressure monitoring. It is used for the diagnosis of ischaemic heart disease (ST segment depression >1 mm, fall in blood pressure or angina), and the assessment of asymptomatic valvular disease and exercise related arrhythmias. Its usefulness is limited in patients on beta-blockers, those with limited exercise tolerance due to co-morbidities and those with resting ECG abnormalities.
Coronary CT angiogram (CTA): advances in CT imaging technology, including the introduction of multidetector (multi-slice) row systems with electrocardiographic gating, have made imaging of the heart and the coronary arteries feasible. Cardiac CTA can provide information about coronary anatomy and left ventricular function that can be used in the evaluation of patients with suspected or known CAD. It is also useful to visualize previous coronary grafts in patients planned for redo cardiac surgery. In most circumstances, a negative coronary CT angiogram rules out significant obstructive coronary disease with a very high degree of confidence, based on negative predictive value of 93% obtained in cohorts. Therefore it is useful for managing patients scheduled for non-coronary artery cardiac surgery particularly in the surgery of aortic root aneurysms where it may be difficult to engage the coronary ostia in angiography. On the contrary, the positive predictive values probabilities following a positive coronary CT angiogram are more variable,
Olivia Swingland MBBChir MSc is a Clinical Fellow at the Royal Free Hospital, London, UK. Conflicts of interest: none declared. Kunal Bhakhri MRCS is a Cardiothoracic Registrar at The Hammersmith Hospital, London, UK. Conflicts of interest: none declared. Jon Anderson FRCS is a Cardiothoracic Consultant at the Hammersmith Hospital, London, UK. Conflicts of interest: none declared.
SURGERY 33:2
52
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
techniques already described, particularly echocardiography, cardiac MRI and cardiac catheterization.
due in part to the tendency to overestimate disease severity, particularly in smaller and more distal coronary segments or in segments with artefacts caused by calcification in the arterial walls. It can therefore be used concomitantly with myocardial perfusion imaging (MPI). The differences in the parameters measured by MPI (‘function’ or ‘physiology’) and CTA (‘anatomy’) must be considered when making patient management decisions with these studies. Of note, a normal MPI does not exclude the presence of coronary atherosclerosis although it does signify a very low risk of future major adverse events over the short to intermediate term. Conversely, coronary CTA allows detection of some coronary atherosclerotic plaques that are not haemodynamically significant. Neither test can presently identify with any reasonable clinical probability non obstructive coronary plaques that might rupture in the future and cause acute myocardial infarction.
Disease of the thoracic aorta Chest radiograph may show mediastinal widening suggesting an aortic aneurysm. It detects pleural effusions, and a large cardiac silhouette may indicate pericardial effusion. CT aortogram is a valuable investigation for the diagnosis and assessment of thoracic aortic disease, demonstrating aortic atheroma, calcification, ulceration, intramural haematoma, dissection and aneurysm. It is widely available in UK hospitals and is therefore the first-line investigation in the acute setting. Multi-slice CT scanning with three-dimensional reconstruction is essential for preoperative planning for non-emergency thoracic aortic interventions (both surgical and endovascular) and for postoperative evaluation.
Valvular heart disease Echocardiography Transthoracic echocardiogram (TTE) e is the primary investigation for valvular heart disease. It detects most valvular conditions and is widely available in UK hospitals, but the quality of images obtained is operator and machine dependent. Transoesophageal echocardiography (TOE) e provides excellent images of the heart, allowing more detailed examination of the mitral valve and aortic root. It is vital in patients with mitral regurgitation who may be suitable for mitral valve repair. Limitations include the need for sedation or anaesthesia and the availability of a skilled operator to conduct the procedure and interpret the images. Three-dimensional echocardiography e can be performed via a trans-thoracic and trans-oesophageal approach. It can provide a surgeon’s view allowing morphologic evaluation of the valve leaflets especially of the prolapsing segment and measurement of the annulus, thus helping plan surgical strategy. It use as an accurate predictor of surgical closure has been well documented. It also allows a dynamic assessment of the valve following surgical repair, for example the ability to look at the mitral closure line in a loaded ventricle in systole. Four-dimensional echocardiography e is used to provide real-time rendering of the heart based on 3-D reconstructed images.
MRI is the investigation of choice for the screening of chronic thoracic aortic dissection or aneurysm. It avoids the radiation dose of CT and provides excellent images of the aortic tree as well as allowing dynamic assessment of valves and ventricles. It can illustrate subclinical disease using molecular imaging techniques. For example quantifying the proportion of elastin in the aortic wall, therefore identifying patients at risk of aortic dilatation that require follow up and intervention. Additionally, it can demonstrate areas of irregular endothelial permeability thus enabling focused preventative treatment. Moreover, fourdimensional phase contrast MRI scanning (4D PC-MR) provides imaging of the flow in both the true and the false lumens, enabling calculation of the rate of aortic expansion, hence guiding prospective endovascular treatment. Positron emission tomography (PET) is increasingly used with CT. This has the benefit of significantly superior images when performed in combination. It can illustrate aortic wall inflammation, with preliminary studies showing strong correlation between increasing inflammation and worsening outcomes. Echocardiography enables rapid assessment of the aortic valve, root and ascending aorta. It is useful to confirm the presence of a dissection flap and to examine the aortic valve in acute type A dissection. Although views of the arch are limited, echocardiography can also be used to screen for coarctation in patients with bicuspid aortic valve disease.
Cardiac catheterization Coronary angiography e is only performed in patients aged >40 years and in younger patients with significant risk factors for coronary artery disease. Aortography e can help to identify the severity of aortic regurgitation and the presence of aortic root or ascending aortic dilatation. Right-heart catheterization e is useful in patients with mitral or tricuspid valve disease, congenital heart disease, pulmonary hypertension and severe left ventricular dysfunction.
Preoperative assessment of fitness for surgery Risk stratification models: objective assessment of surgical risk is undertaken to facilitate better informed consent. Surgical risk is influenced by co-morbidity: diabetes chronic pulmonary disease renal dysfunction neurological dysfunction peripheral vascular disease endocrine disease obesity or frailty.
Structural disease of the heart Non-valvular heart disease such as atrial or ventricular septal defects, more complex adult congenital heart disease, pericardial fluid or thickening can be identified and evaluated using
SURGERY 33:2
53
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
The effect of risk factors on surgical outcome has been defined by risk stratification models The EuroSCORE I and II were developed using data from 128 European cardiac surgical centres. They remain the most commonly used scoring algorithm in Europe, incorporating 17 risk factors analysed as both additive and logistic scores. The original EuroSCORE I was criticised for over-estimating the risk of mortality; however, following a database update in 2011 EuroSCORE II was published. This is not only used for preoperative risk calculation but also for risk-adjusted evaluation of the postoperative mortality using Cumulative Sum Control Chart (CUSUM) analysis. This reflects the improving surgical outcomes associated with preoperative screening, surgical techniques and intensive care advances. EuroSCORE has comparable predictive value in both North America and Europe. The Bayes Model is the preferred method of risk stratification recommended by the Society for Cardiothoracic Surgery in Great Britain and Ireland (SCTS). Variations of the model exist, differing in the number of factors used to calculate the final risk score. The Bayes model requires more complex computer calculations of risks scores but more accurately reflects the target population.
History-taking and examination: specific questions and examinations relevant to cardiac surgery are listed in Table 1. Full blood count: unexplained anaemia (haematocrit <35%) is investigated and referred to a haematologist or gastroenterologist if appropriate. Stable patients may commence iron supplements or erythropoietin therapy preoperatively. A high white cell count (>11,000 per mm3) suggests underlying infection and should be investigated before elective surgery. Extensive research has illustrated significantly worse postoperative outcomes (mortality, length of hospital stay) when surgery was performed in the presence of intercurrent infection and raised CRP. A platelet count <100,000 per mm3 can indicate idiopathic thrombocytopenia or thrombotic abnormalities and should be referred to a haematologist. Coagulation: prothrombin time activated partial thromboplastin time and platelet count should be measured preoperatively. Abnormalities can be corrected using vitamin K, fresh frozen plasma and platelet transfusions if necessary. Patients on warfarin or heparin should have INR and APTT checked, respectively. Warfarin should be stopped 5 days before surgery if possible.
Preadmission clerking and investigations: the trend towards preadmission clinics is now well established. Generally led by junior doctors and nurse specialists, these sessions are valuable because: Patients and relatives can be familiarized with the hospital environment as they are invited to tour the wards and the intensive care unit. Preoperative tests can be streamlined and results are available well in advance of the scheduled surgery so abnormalities can be corrected or investigated before admission. These can then be discussed in multi-disciplinary meetings, an approach proven to improve both early and long-term outcomes. Patients have ample opportunity to ask further questions regarding their disease and the proposed surgery, thereby reinforcing informed consent.
Urea and electrolytes: hypokalaemia is a common abnormality seen in patients on diuretics and may cause premature ventricular ectopics, ventricular tachycardia and ventricular fibrillation. Raised creatinine (>120 mmol/l) indicates pre-existing renal impairment. Creatinine clearance can be calculated from the Cockcroft-Gault equation (Box 1). Patients with GFR <60 ml/min are at risk of developing postoperative renal failure requiring temporary or permanent haemodialysis. Biomarkers: the addition of specific biomarkers to preoperative investigations remains centre specific. The exception being Troponin T and I as an indicator of ongoing compromise to cardiac perfusion. Raised preoperative Troponin levels have been linked to prolonged ICU stay, increase in adverse outcomes including mortality.
History-taking and examination relevant to cardiac surgery History
Coronary risk factors
Examination
Medical history Surgical history Cardiovascular
Conduits for CABG Peripheral vascular disease BMI Dental hygiene
Smoking, hypertension, diabetes, hypercholesterolaemia, family history, socioeconomic status Respiratory, neurological, peripheral vascular, renal, hypothyroidism, PUD Including previous cardiac surgery Heart murmur in patients for CABG mandates echocardiogram Heart failure (beneficial to off-load prior to elective surgery) Carotid bruits Varicose veins/surgery Allen’s test to assess radial artery Relative contraindication to intra-aortic balloon pump Height and weight: Obesity and frailty increase risk Dental check essential for patients with heart valve disease
Table 1
SURGERY 33:2
54
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
The Cockcroft-Gault equation for calculating creatinine clearance Creatinine clearance ðmenÞ ¼
ð140 ageÞ weight ðkgÞ ðin women 0:85Þ 72 serum creatinine ðmg=100 mlÞ
Box 1
Variations in levels from the physiological norm of brain natriuretic peptide, vitamin D and growth differentiation factor 15 have also been linked with increased adverse events postoperatively. Monitoring these biomarkers may become more widespread as the demographic requiring surgery changes. Meticillin-resistant Staphylococcus aureus (MRSA) screening has been introduced on all patients preoperatively to help reduce the incidence of MRSA infection. Patients with positive swab results are given suppression therapy to reduce the risk of self-infection. Better hygiene and precautions taken by staff helps to prevent cross-contamination.
arrhythmias during surgery, with relevant medications being continued until surgery. A chest radiograph is an essential preoperative investigation to exclude coexisting lung disease (e.g. chronic obstructive pulmonary disease, lung fibrosis and carcinoma). Pulmonary function tests are routinely undertaken; however, they are of increased importance in patients who are heavy smokers or have chronic obstructive pulmonary disease or asthma. Baseline preoperative tests include bedside spirometry, pulse oximetry and arterial blood gas analysis. Patients with FEV1 <50% of predicted should have laboratory pulmonary function tests and referral to a respiratory physician. FEV1 <65% of vital capacity or FEV1 <1.5 e2.0 l predicts prolonged ventilator wean postoperatively.
12-lead ECG is always done as a baseline. It may reveal arrhythmia, conduction defect, myocardial infarction and ventricular hypertrophy. Preoperative control of heart rate prevents
Figure 1
SURGERY 33:2
55
Ó 2014 Published by Elsevier Ltd.
CARDIOTHORACIC SURGERY I
Summary
Carotid Doppler is done in patients with: history of cerebrovascular accident or transient ischaemic attack carotid bruits peripheral vascular disease. The optimal surgical approach for coexistent significant carotid stenosis and coronary artery disease remains a contentious issue and is best determined on an individual patient basis. The essential role of multidisciplinary team meetings with combined cardiology and cardiothoracic team presence for discussing complex patient’s diagnoses, management and prognosis is usually carried out after some investigations have been performed. The role of these meetings has been proven to improve both short and long term patient outcomes.
SURGERY 33:2
Figure 1 illustrates the pathway taken by candidates for cardiac surgery. A FURTHER READING Cohn LH. Cardiac surgery in the adult. 4th edn. New York: McGraw-Hill, 2011. Swanton RH, Banerjee S. Swanton’s cardiology: a concise guide to clinical practice. 6th edn. Oxford: Blackwell Science, 2008.
WEBSITES http://www.scts.org/sections/audit/Cardiac/index.html. http://www.ctsnet.org/doc/2692. http://www.euroscore.org.
56
Ó 2014 Published by Elsevier Ltd.