Essay: Risk assessment in cardiac disease cases

GENERAL INTRODUCTION
The magnitude of the problem
It is estimated that 1.3 million non-cardiac surgical procedures are performed annually in the United Kingdom, with 166,000 being high-risk procedures (Pearse et al., 2006). Differences in incidences between the studies reviewed by Poldermans et al. (2009) suggest that major non-cardiac surgery is associated with an incidence of cardiac death of between 0.5-1.5%, and of major cardiac complications of between 2.0-3.5%. When these figures are applied to the European population it is predicted that up to 250,000 life-threatening cardiac complications resulting from non-cardiac surgery will occur per year. The increasing aging population is thought to have a major impact on perioperative patient management and although mortality from cardiovascular disease is decreasing in the general population, the prevalence of ischaemic heart disease (IHD), heart failure, and cardiovascular risk factors such as, diabetes, is increasing (Naughton and Feneck, 2007). Elderly patients typically present for surgery with significant comorbidities, cardiovascular disease being the most prevalent. Carroll et al. (2003) estimates that 19% of men and 12% of women aged 75 to 85 have some degree of cardiac disease which is an important factor when considering perioperative management, as elderly people are four times more likely to require surgery than the general population as estimated by Naughton and Feneck (2007). Statistics, published by the British Heart Foundation (BHF), predict that cardiac disease alone causes 48% of deaths within Europe and 42% of deaths within the European Union (EU). It is thought that cardiovascular disease costs the EU economy ‘192 billion each year: 57% being healthcare costs, 21% production loss and 22% informal care of individuals (BHF, 2008).
Why is risk assessment essential?
The risk of cardiac perioperative complications are highly dependent on the age, comorbidities and the nature of the surgical procedure being performed. Surgeons and anesthesiologists utilise risk stratification tools, coupled with their clinical expertise, to assess patients preoperatively to identify, avoid or plan for adverse outcomes. It is important to assess the patient preoperatively as cardiac complications can arise in patients with documented or asymptomatic IHD, left ventricular dysfunction, and valve disease in non-cardiac surgery are associated with prolonged cardiac stress and a reduction in hemodynamic stability (Poldermans et al., 2009). Accurate estimates of perioperative cardiac risk will identify people who may benefit from optimisation of chronic medical treatment, interventions such as coronary revascularisation, aggressive haemodynamic management, closer postoperative surveillance, or avoidance of surgery (Wijeysundera et al., 2011). The tables below are used by clinicians to risk-stratify patients preoperatively, based on the nature of the surgery (see Table 1.1) or based on the American Society of Anesthesiology (ASA) patient fitness grades (see Table 1.2).
Table 1.1- Surgery Grades
Grade Example
1 ( Minor) Excision of skin lesion, drainage of breast abscess
2 (Intermediate) Primary repair of inguinal hernia, excision of varicose veins, tonsillectomy
3 (Major) Total abdominal hysterectomy, endoscopic resection of prostate, thyroidectomy
4 (Major??+) Total joint replacement, lung operation, colonic resection, radial neck resection
Neurosurgery Evacuation of subdural haematoma
Cardiovascular surgery Coronary artery bypass grafting
Table 1.1- A table showing surgical grades adapted from the NICE (2003) publication: Preoperative tests as cited by Chikwe et al. (2009).
Table 1.2- ASA patient fitness grades
ASA grade Description
1 ‘Normal healthy patient’ i.e. without any clinically important comorbidity and without clinically significant past/previous medical history.
2 ‘ A patient with mild systemic disease’ no functional limitation’
3 ‘ A patient with severe systemic disease with definite functional limitation’
4 ‘ A patient with severe systemic disease which is a constant threat to life’
Table 1.2- A table showing how patient fitness is classified into American Society of Anesthesiology (ASA) patient grades, adapted from the NICE (2003) publication: Preoperative tests as cited by Chikwe et al. (2009).
Preoperative investigations
Preoperative stratification of patients can be complex, investigations, such as: blood tests, a pregnancy test, electrocardiogram (ECG), Chest X-ray (CXR), Arterial blood gases (ABGs), pulmonary function testing (PFT’s) and echocardiography can be requested and performed to identify any risk to surgery. Although preoperative investigations can be useful, most tests are low yield in young patients and most abnormal findings will not change management in minor surgery (Chikwe et al., 2009). Following guidance from the NICE (2003) publication: Preoperative tests, no preoperative tests are required for healthy adults below 80 years of age whom are undergoing minor surgery. To optimise treatment appropriate request by the clinician is vital, to reduce waiting times for preoperative tests and surgical procedures, and to reduce the cost of inappropriate preoperative tests, Fleisher et al. (2007) recommends that no test should be performed unless it is likely to influence patient’s treatment. Although transthoracic echocardiography (TTE) is not a routine preoperative investigation, TTE can effectively assess the anaesthetic risk in patients with known or suspected cardiovascular disease. Table 1.3 shows the indications for requesting preoperative TTE as recommended by BSE (2012) guidance.
Table 1.3 – Pre-Operative Echocardiography for Elective and Semi-urgent Surgery
Indicated Not indicated
a. Documented ischaemic heart disease with reduced functional capacity (<4 METS) a. Repeat assessment of previous echocardiogram with no intervening change in clinical status b. Unexplained shortness of breath in the absence of clinical signs of heart failure if ECG and/or CXR abnormal b. Routine pre-operative echocardiography c. Murmur* in the presence of cardiac or respiratory symptoms d. Murmur* in an asymptomatic individual in whom clinical features or other investigation suggest severe structural heart disease *which is pathological in nature efficiently assessed by a clinician. Table 1.3- shows the indications for preoperative TTE adapted from the British society of echocardiography (BSE, 2012). Transthoracic echocardiography (TTE) and anaesthetic risk Echocardiography techniques were first developed in 1953 by cardiology physician Edler and physicist friend Hertz. Edler primarily used the M-mode (motion mode) echocardiography for the preoperative evaluation and diagnosis of mitral stenosis of mitral regurgitation (Singh and Goyal, 2007). M-mode images depict a single line of ultrasound overtime and although this technique is still used today, other transthoracic ultrasonic methods are available, these include: two-dimensional (2D) echocardiography, three dimensional (3D) echocardiography and Doppler imaging (pulsed, continuous wave (CW), imaging CW and colour flow) (Ramrakha and Hill, 2008). It is now common practice to use standard 2D TTE to aid the diagnosis of cardiovascular disease. Many image planes can be used to visualise the valves and chambers of the heart. TTE evaluates valve anatomy, aetiology of disease and severity of stenosis and regurgitation. TTE is also used to visualise the consequences of valve disease including: left ventricular (LV) hypertrophy, dilation, impact on systolic and diastolic function, effects on other cardiac chambers and changes in pulmonary pressures or vascular resistance (Bonow and Otto, 2014). TTE frequently influences the management of patients when undergoing anaesthetic in non-cardiac surgery, the reason for this being that patients with cardiovascular disease (where aortic stenosis poses the greatest risk) have an increased anaesthetic risk of cardiac mortality or morbidity (Acton, 2013). Physicians will use echocardiography to assist the diagnosis of valve disease and left ventricular dysfunction preoperatively to ensure the correct measures are taken to anaesthetise the patient safely. Moderate to severe Aortic stenosis poses the greatest risk which can cause anaesthesia related problems including: fixed cardiac output, ventricular arrhythmias and incipient cardiac failure (Smith et al., 2009). Other valve diseases: Aortic regurgitation, Mitral stenosis and regurgitation can also significantly increase the anaesthetic risk while tricuspid valve and pulmonary valve lesions are rarer and carry less risk. Moderate to severely impaired left ventricular function also places the patient at higher risk for perioperative cardiac morbidity and mortality (Nagelhout and Plaus, 2013). Aortic stenosis and the anaesthetic risk assessment using TTE In 1977, Goldman et al. identified aortic stenosis (AS) as an independent risk factor for the development of cardiac complications in non-cardiac surgery. The conclusions from the Goldman et al. (1977) prospective study were that patients with AS in non-cardiac surgery had a 17.3% risk of cardiac complications and a 13% mortality rate compared with 1.6 % in patients without AS. It is important that physicians and other healthcare professionals can identify a cardiac murmur and distinguish between innocent or pathological aetiology. Pathological cardiac murmurs can suggest valve disease, stenosis or regurgitation, including aortic stenosis (Fleisher et al. 2007). Severe AS poses the greatest risk for non-cardiac surgery. If the AS is symptomatic, elective non-cardiac surgery should be postponed or canceled and an Aortic valve replacement may be required. If asymptomatic the surgery should be deferred or canceled if the valve has not been recently evaluated. In contrast, patients with severe AS who refuse Aortic valve replacement surgery or are not suitable non-cardiac surgery can be performed with a mortality risk of approximately 10% (Fleisher et al. 2007). However critical analysis by Samarendra and Mangione (2015) of old and new data from published reports, suggests that the significance of AS is exaggerated in patients undergoing non-cardiac surgery before recent advances in: TTE, cardiac catheterisation in the assessment of AS, anaesthetic, surgical techniques and also post-operative patient care. The anaesthetic risk associated with AS during non-cardiac surgery depends on the severity of the disease, patient fitness and complexity of the surgery (Samarendra and Mangione, 2015). The reason for the increased risk during non-cardiac surgery in AS is that the decrease in systemic vascular resistance caused by many of the anaesthetic drugs available, results in a marked fall in blood pressure because the cardiac output is relatively fixed. The fall in blood pressure reduces coronary perfusion of a left ventricle which is hypertrophied and may result in ischaemia, reduced contractility, and a vicious spiral of a further falling blood pressure. The onset of LV failure has poor prognosis and the valve gradient should be interpreted with a measure of left ventricular function because with time the left ventricle will fail and the measured gradient will start to fall. If aortic stenosis is severe, anaesthesia and spinal anaesthesia should be avoided if possible however it may be possible to use an epidural or general anaesthetic but drugs should be administered slowly (with invasive blood pressure measurements) so that falls in systemic vascular resistance can be treated promptly. Hypotension should be treated by an alpha antagonist such as (metaraminol) to minimise risk of ischaemia induced by tachycardia, a CVP line or other measure of LV filling is also helpful to diagnose and appropriately treat hypotension (Allman and Wilson, 2002). To assess the Aortic valve for stenosis preoperatively, TTE is performed using the standard protocol as recommended by the BSE (2012) which provides a holistic assessment of all cardiac chambers and valves. When aiming to identify AS alone, the following specific modalities provide the diagnostic criteria, these are: ' M-mode ' The valve will appear to be calcified with restrictive opening. ' CW Doppler- to assess the velocity (pressure gradient) across the valve. ' Colour Doppler ' to identify any concomitant Aortic regurgitation (Ramrakha and Hill, 2008). Completion of the TTE provides technicians and physicians with valuable data, which can then be used to assess the severity of Aortic Stenosis (AS) and other existing cardiac abnormalities detected. The prognosis of AS is poor once there is a mean aortic valve gradient of >40 mmHg. Lower aortic valve velocities and lower aortic valve gradients can present in patients who have low forward flow, therefore aortic valve area (AVA) should be calculated. An AVA of <1.0 cm2 is related to a poorer prognosis and patients with calcified AS and an AVA between 0.8 and 1.0 cm2 should be monitored closely to evaluate the need for valve replacement or intervention (AHA/ACC, 2014). Severe symptomatic AS with a gradient of >80 mmHg if left untreated had a 50% 1 year survival rate (Allman and Wilson, 2002). Below Table 1.4 provides detailed recommendations for classification of AS severity.
Table 1.4 ‘ Recommendations for classification AS severity.
Aortic sclerosis Mild Moderate Severe
Aortic jet velocity (m/s) ‘2.5 m/s 2.6-2.9 3.0-4.0 >4.0
Mean gradient (mmHg) <20 (<30a) 20-40b (30-50a) >40b (>50a)
AVA* (cm2) >1.5 1.0-1.5 <1 Indexed AVA* (cm2/m2) >0.85 0.60-0.85 <0.6 Velocity ratio >0.50 0.25-0.50 <0.25 aESC Guidelines bAHA/ACC Guidelines *AVA- Aortic Valve Area Table 1.4- adapted from ESC /ASE (2009) and AHA/ACC (2014) guidelines, shows how the severity of Aortic stenosis is categerised. Although TTE is a highly validated method for detection of AS, other investigations may be required to assess the Aortic valve, such as: transoesphageal echocardiography (TOE), computed tomography (CT), exercise tolerance testing (ETT) and cardiac catheterisation to optimise management and treatment for the patient. An evaluation of the possible surgical risk for each individual patient should be performed if intervention is contemplated, as well as other contributing factors such as the presence and extent of comorbidities and frailty. Meticulous attention to detail is required when assessing aortic valve hemodynamics, either with Doppler echocardiography or cardiac catheterization, and the inherent variability of the measurements and calculations should always be considered in clinical-decision making (Ramrakha and Hill, 2008). Left ventricular function and the anaesthetic risk assessment using TTE Congestive heart failure (CHF) is the consequence of left ventricular (LV) dysfunction, the aetiology of the disease by coronary artery disease and diabetes has increased, whereas hypertension and rheumatic valve disease has decreased. The Framingham heart study as cited by Armstrong (2000) suggests that CHF develops in approximately 16% of men and 18% of women who have diabetes; 12% of men and 8% of women who have hypertension; and 30% of both sexes who have had a myocardial infarction (MI). Routine echocardiography is not recommended for the pre-operative evaluation of LV function, but may be performed in asymptomatic patients undergoing high-risk surgery. A meta-analysis of the available data demonstrated that an LV ejection fraction of <35% had a sensitivity of 50% and a specificity of 91% for prediction of perioperative non-fatal MI or cardiac death. The limited predictive value of LV function assessment for perioperative outcome may be related to the failure to detect severe underlying IHD (Poldermans, 2009). LV function is a significant predictor of cardiac morbidity and mortality. The role of TTE in the assessment of LV function is well established and has been expanded over the last few years with the development of new methodologies. Echocardiography can assess LV global and regional function and also the systolic and diastolic function. TTE also has the capability to measure volumes, including cardiac output, pressures, LV mass and dP/dt. TTE can also measure regional dysfunction using the wall motion score. TTE is an important method of assessing the LV function, which is important when used to assess anaesthetic risk preoperatively (Pinto, 2004). When the LV function is compromised, it can be problematic to wean the patient from cardiopulmonary bypass, which may result in subsequent low cardiac output and decreased tissue perfusion in the postoperatively . Severe hypotension is another major problem during induction of anaesthetic (Brezina et al., 2009). Other cardiac disease and anaesthetic risk assessment using TTE All cardiovascular disease will have some impact in non-cardiac surgery; TTE can be used to assess the severity of disease in: heart failure, cardiomyopathy, valve disease including prosthetic valves, post cardiac transplant, pericardial disease and congenital heart disease. But in other cardiovascular disease other methods are more beneficial these include: IHD (where exercise tolerance testing or angiography may be utilised), arrhythmias (where a 12-lead ECG or ambulatory ECG may be utilised) or even hypertension (which may be monitored using ambulatory blood pressure recordings) (Allman and Wilson, 2002). Appropriateness of TTE and effects on perioperative management In recent years, there has been a dramatic increase in the use of cardiovascular diagnostic imaging. Findings from Medicare's physician fee schedule as cited by Ward et al. (2008) suggests that cardiovascular imaging has grown more rapidly than any other type of service from 1999 to 2003 (see Figure 1). The dramatic increase in TTE requests has resulted in scrutiny of the appropriateness for TTE's, especially when not requested by a cardiology specialist (Ward et al., 2008) Figure 1- shows the number of imaging services between 1999 and 2004 among Medicare enrolees. Adapted from Pearlman et al. (2007) as cited by Ward (2009). Preoperative clinics can improve efficiency by enabling early review of the notes of complex cases, and to ensure that appropriate investigations are requested and performed or to ensure that specialist referrals are made if necessary (Verma et al., 2011). NICE (2003) guidance on preoperative tests is often used, but clinical expertise and judgment is often is important as inappropriate or unnecessary investigations may be increased in nurse-led clinics or when requested by junior physicians. Although preoperative investigations are widely used, a study by (Chung et al., 2009) shows that there was no difference in the outcomes of day surgery patients even when all pre-operative investigations were undertaken. To ensure that patients receive high quality of care, the American College of Cardiology Foundation as cited by Ward et al. (2008) published Appropriateness Criteria (AC) for cardiac imaging, which includes TTE. Recently, the ACCF and ASE also cited by Ward et al. (2008) published the appropriateness criteria for Transthoracic and Transoesophageal Echocardiography. Although appropriate criteria is a useful tool to assess the patients need for preoperative tests, it not solely used as clinical presentation, history and comorbidities may interfere with the criteria and should not be substitutes for clinical judgement. Although ACCF/ASE gave guidance for indications of TTE, they do not provide guidance on pre-operative echocardiography alone. Many surgical procedures are delayed or cancelled due to inadequate preoperative assessment, investigations and preparations. Study by Conway et al. (1992) Shows that 60% of referrals to the preadmission consultation clinic were related to the cardiovascular system, with 27% of these being coronary artery disease. The results of this study also conclude that preadmission clinics potentially reduce hospital costs and improve surgical efficiency. ACC/AHA (1997) recommends that when considering which preoperative investigations should be used, factors such as: local expertise in performance and interpretation, test availability, cost, and patient preference should be assessed. TTE is associated with little if any patient discomfort, and no risks with this procedure have been identified. The findings of the study conducted by Martin and Picard (2009) were that TTE studies requested by the ward service were 89% appropriate, and those ordered by the non-ward service were 80% appropriate although the majority were ordered appropriately, all inappropriate referrals will lead unnecessary costs to the healthcare service, also longer waiting times for preoperative TTE's. There have been many studies which review the appropriate criteria AC for TTE, but there are limited studies directed at the appropriateness of preoperative TTE's. Preoperative echocardiography was not associated with improved survival or shorter hospital stay after major non-cardiac surgery. These findings highlight the need for further research to guide better use of this common preoperative test (Wijeysunder, 2011). The study by Canty et al. (2012) concluded that after TTE the diagnosis of cardiac disease was changed in almost 70% of patients and the perioperative management plan was changed in 44%. Patients that TTE identified cardiac disease, led to a step-up in treatment in 36% of patient, which included: delay in surgery for a cardiology referral, altered surgical methods, intensive care and an increase in intra-operative haemodynamic management. In contrast patients in which TTE did not identify cardiac disease resulted in a step- down of treatment in 8%, which included: no referral to cardiology, intensive care or haemodynamic treatment. Precise pre-operative cardiac assessment is essential to devise the most suitable anaesthetic plan. Within the population requiring hip replacement, AS and pulmonary hypertension are significant risk factors for mortality, but without assessment using TTE diagnosis is unreliable. Other abnormal haemodynamic states such as: hypovlaemia, Left ventricular dysfunction, right heart failure and sepsis (vasodilation) often accompany acute surgical disease, and may contribute to impaired cardiac output and tissue perfusion perioperatively if not adequately treated. Pre-operative transthoracic echocardiography (TTE) can determine haemodynamic state, valve disease and can assist in estimation of cardiac risk, therefore facilitating assessment and treatment changes before surgery. Importance of the study Within the NHS there is a legal right to start consultant-led treatment within a maximum of 18 weeks from referral although this is not the case if individuals choose to wait longer or it is clinically appropriate to do so (NHS, 2013). Therefore, the longer the waiting time for the TTE is the less likely that the patient will be seen within these limits. This research aims to reduce waiting time by preventing inappropriate referrals which lead to inappropriate testing therefore longer waiting times for both appropriate/inappropriate referrals. Inappropriate requesting will also cause additional expense to the department even though TTE is cost effective compared to MRI or CT scanning. Furthermore request forms that are being filled out incorrectly/ lack information will lead to some inappropriate TTE's being performed, the researcher will report back to the requesters for the required clinical details and as result of the service evaluation the researcher expects a new request form will be designed to avoid this. Aims What impact do the results of preoperative TTE's have on the anaesthetic management of the patient and what is the impact on the current service when requested appropriately or inappropriately? The service evaluation aims to identify if referrals are indicated, not indicated or if the forms are incorrectly filled in or lack important information, from this the researcher will gain understanding of the patient care currently in place. The researcher intends to highlight areas for assessment, improvement and expansion from the analysis. Once the results are analysed it is then possible for the department to identify the outliers and report back to the requester to improve the service by: filling out the forms correctly and revising guidelines which will decrease inappropriate referrals as well as TTE and surgical waiting times. However if most patients are referred appropriately then the department will have to develop the service and increase resources.