TRANSTHORACIC ECHOCARDIOGRAPHY (TTE) An overview for Perioperative Care Dr Andrew Cluer, Sydney, Australia 2015 This piece of work is not meant to teach students echo interpretation, but instead offers an insight into interpretation and gives the reader a broad understanding of the uses and limitations of this powerful technology. It is important to recognise from the outset that echo data should be considered in clinical context and as such is useful when it corroborates clinical suspicions and often misleading when used in isolation. This is particularly so when a doctor says I know, lets get an echo! Both images and clips are included for student interest. By way of introduction and for those students who have never been introduced to the technical aspects of ultrasound, Wikipedia is on hand to help! This link acts as a good introduction, but it is not considered essential reading for this echo review. Rather the piece adds value where students would like to read more widely. https://en.wikipedia.org/wiki/medical_ultrasound Indications for resting preoperative transthoracic echocardiogram (TTE) have been published by the European Society of Cardiology (ESC)/European Society of Anaesthesiology (ESA), British Society of Echocardiography (BSE) and American Heart Association (AHA)/American College of Cardiology (ACC) (see links at the end of the document). For ease of reading the documents have been summarised in Table 1. These guidelines are extremely useful but it is worth noting they do not adequately address some important issues such as suspected or known pulmonary hypertension (PHT). Where deficient supplemental links are provided. In general terms the advantages of resting preoperative Trans Thoracic Echocardiography (TTE) in non-cardiac surgical patients are not entirely clear. Wijeysundera et al. (2011) retrospectively looked at over 260,000 patients who had undergone medium or high risk non-cardiac surgery and found that preoperative resting TTE was not associated with either a decreased hospital stay or an improved survival. Although retrospective this very large study suggests that much more research needs to be done to define which patients benefit from an increasingly common preoperative investigation. A relatively recent editorial in Anaesthesia (Heyburn & McBrien 2012) has actually advocated resting preoperative TTE for all patients with hip fractures though these recommendations are not reflected in any current international guidelines. Despite the above it is generally accepted that for specific individuals TTE can have a major impact on their perioperative clinical management. TTE enables rapid assessment of cardiac structure and function. It has certain advantages over Transoesophageal Echocardiography (TOE) including superior assessment of aortic valve areas and gradients, better imaging of the left ventricular apex and more accurate assessment of ejection fraction (EF%). It is also non-invasive, quicker and involves minimal risk to the patient. Indications for TOE include imaging of the mitral valve prior to cardiac surgery, detailed assessment of atrial structures,
suspected aortic dissection and investigation of endocarditis and is rarely indicated in the perioperative period. It is important to understand that TTE is a snapshot at one particular point in time. This is not an issue in euvolaemic, hemodynamically stable patients but can be of relevance at other times in the perioperative period. In the unstable patient measurements made using TTE can change rapidly and are dependent on many factors including volume loading, inotrope use and lung ventilatory settings. It may therefore be appropriate to carry out serial examinations in the perioperative period, echo being used as a monitor rather than a diagnostic tool. It is also important to understand that TTE is a snapshot at rest and therefore has a very limited role in the preoperative assessment of ischaemic heart disease. Recommendations on preoperative imaging stress testing are included in the ESC/ESA and AHA/ACC documents mentioned above. A skilled echocardiographer will always acquire a set of standard views and measurements however, they will seek to obtain extra information dependent on the patient information provided. It is therefore essential that TTE referrals state the clinical question to be answered. A comprehensive echocardiographic assessment of pulmonary hypertension is very different to an assessment of aortic stenosis. A case study in heart failure Mrs P is a 60 years old lady reviewed in the surgical pre-assessment clinic prior to planned Oesophagectomy for cancer. The patients past medical history includes:- Paroxysmal Atrial Fibrillation (anticoagulated) Non-Insulin Dependent Diabetes Mellitus New onset paroxysmal nocturnal dyspnoea and orthopnoea Exercise tolerance is currently 50 metres on the flat A systolic murmur is heard on auscultation The TTE request states Please assess biventricular function, pulmonary pressures and check for any valvular pathology. Mrs P s TTE report provides an overall picture of her cardiac structure and function. Like all reports it should make sense clinically and the individual components must fit together. For example, severely impaired left ventricular (LV) systolic function will generally be associated with some diastolic dysfunction, severe mitral regurgitation (MR) will generally be associated with significantly raised pulmonary pressures and significant diastolic dysfunction will generally be accompanied by a large left atrium. Aspects of a TTE report that do not make clinical sense imply some errors in measurement may have been made and should be viewed with suspicion. Understanding the overall message an echocardiographer or cardiologist is trying to convey with a TTE report is more important than simply focusing on isolated numbers such as ejection fraction (EF%). The reference ranges of most TTE
measurements are affected by age and sex. Many measurements should also be indexed to Body Surface Area (BSA) so a patient s height and weight should ideally be recorded (when was the last time you included this data in your request for investigation?). For example a Left Ventricular End Diastolic Diameter (LVEDD) of 6.0cm can be normal for a large man but very abnormal for a small woman. The British Society of Echocardiography smartphone app. is free to download and is a useful reference for normal and abnormal values. Medical practitioners often view a TTE report as a bewildering array of data and focus only on the short written conclusion which can occasionally be falsely reassuring. It is important to understand that an echocardiographer and clinician may regard different aspects of a TTE report as being significant. To get the most out of a report it is better to try and separate the meaningful data from the less helpful measurements and gain a deeper understanding of all the information provided. For example EF% (measured by Simpsons Biplane technique) is a validated and reproducible measurement, whereas EF% (measured by Teichholz technique) is not. A summary of the most useful measurements on a TTE report is provided in Table 2 and the following discussion aims to provide some guidance on how to interpret the data. Understanding the detail: A guide to echo interpretation The detail below is not meant to be memorised, rather the student should begin to understand what elements of the investigation are globally assessed (often with the experienced eyeball) and which are measured. For both elements of assessment it is important to appreciate the scope for error. 1. LEFT VENTRICLE: Assessment of the left ventricle should be divided into structure and function (systolic and diastolic). Structure - The most important aspects of LV structure are size and wall thickness. Both are measured at end diastole on a Parasternal Long-Axis View (PLAX) (Video 1 - PLAX) The thickness of the interventricular septum (IVS) and posterior wall (PW) is routinely reported along with any other abnormalities such as asymmetric hypertrophy or scarred myocardium. Structure of the LV also includes other pathology such as thrombus or septal defects. Simple 2-D measurements (see wiki link to understand these modes of imaging) are generally more accurate than M- Mode, which can overestimate the LV diameter if not careful. It is important to note that isolated basal septal hypertrophy can be a normal finding in the elderly and should not be confused with hypertrophic cardiomyopathy. Mrs P: LV Diastolic Diameter = 5.6cm, IVS = 0.9cm, PW = 1.0cm. Conclusion = mildly dilated LV with normal wall thickness. (Image 1 LV Size & Wall Thickness)
Image 1 Systolic Function - LV systolic function can be globally or regionally impaired. Quantification of systolic function is best achieved by calculating an EF% using Simpson s Biplane method. Views required are the Apical 4 Chamber (Video 2 A4C) and Apical 2 Chamber (Video 3 - A2C). On occasions an experienced echocardiographer will visually estimate the EF% or simply quantify systolic function as good overall function or mild, moderate or severe impairment. It is an interesting and important fact that visual estimates by experienced practitioners are as useful as a calculated EF%. Regional wall motion abnormalities (RWMA) usually imply ischaemic heart disease and their distribution often assists in determining the specific coronary artery affected. For example, an akinetic LV apex and anterior septum is likely secondary to disease of the left anterior descending coronary artery. RWMA can be subtle and difficult to identify and there are often variations in reporting between echocardiographers. Segmental basal inferior and inferoseptal hypokinesis is commonly reported and of little significance. Apical akinesis should always raise the suspicion of a thrombus and some departments will routinely investigate with a contrast study. Mrs P: LV Ejection Fraction = 20.2%. Conclusion = Global, severe impairment of systolic function. (Image 2,3,4 & 5)
Image 2
Image 3 Image 4
Image 5 Diastolic Function (dysfunction - alternatively known as heart failure with preserved ejection fraction). LV Diastolic function assessment is complex and interested readers are directed to ESC guidelines on this topic (Link provided at the end of the document). An important distinction to make is whether there is isolated LV diastolic dysfunction or does it accompany LV systolic dysfunction. Traditionally diastolic dysfunction is graded (1-4) using Doppler patterns from mitral inflow (Mitral E and A waves) and tissue Doppler from LV Septal (E Septal Velocity) and LV Lateral Walls (E Lateral Velocity). Grade 1 dysfunction is defined as impaired relaxation whereas Grade 4 dysfunction is defined as irreversible restrictive disease. In the presence of normal systolic function it is appropriate to grade diastolic dysfunction in this manner. Importantly type 1 diastolic dysfunction in the elderly is a normal finding. E/E ratio is the most useful measurement and an E/E Septal > 15 or E/E Lateral > 12 is abnormal. Diastolic dysfunction is generally always present in patients with significantly impaired LV systolic function and in this situation it makes more sense to try and quantify elevations in left atrial pressure. E/E is useful and will increase as left atrial pressure (LAP) increases. E/E is therefore a dynamic measurement and changes with fluid loading. Mrs P: Mitral E to LV E Septal Ratio = 39.4. Conclusion = Severely elevated LAP (Image 6 Mitral E & A Waves, Image 7 - E Septal Velocity)
Image 6 Image 7
2. RIGHT VENTRICLE: The right ventricle (RV) is best assessed qualitatively for size, structure and function. Few quantitative measurements are useful. If the RV is enlarged and has normal systolic function then it is likely to be volume overloaded (Tricuspid Regurgitation (TR), Pulmonary Regurgitation or Atrial Septal Defect). If the RV is enlarged and has significantly impaired systolic function then possible pathology includes RV pressure overload, cardiomyopathy or infarction. Tricuspid Annular Plane Systolic Excursion (TAPSE) is often quoted as a quantitative measure of RV systolic function but in reality only reflects basal RV function and provides no information about the RV free wall. Mrs P: Qualitative comment Normal RV size and mildly impaired systolic function (Video 4 - RV). TAPSE = 1.5cm (Image 8) Calculation of Right Ventricular Systolic Pressure (RVSP) or Pulmonary Artery Systolic Pressure (PASP) is relatively easy and an extremely useful measurement in the assessment of PHT. RVSP = 4 x (Peak TR Velocity) 2 + Right Atrial Pressure (RAP). RAP is estimated from the size of the Inferior Vena Cava (IVC) and its collapsibility on deep inspiration (Video 5 IVC). It is important to note that pulmonary hypertension is defined by mean pulmonary artery pressure (link provided) and not PASP (or RVSP) which is quoted on a TTE report. Comprehensive echocardiographic assessment of PHT has been outlined in an excellent document written by Hammersmith Hospital Cardiology Department (link provided). Mrs P: TR Peak Velocity = 3.95m/sec, RAP = 10mmHg. PASP =72.4mmHg. Conclusion = moderate/severe elevation in pulmonary pressures. (Video 6 TR Colour Doppler, Image 9 Peak TR Velocity)
Image 8 Image 9
3. ATRIA: Atria are considered as the window to the ventricles. For example the first sign of significant LV diastolic dysfunction is an enlarged left atrium. Qualitative comments about the shape of the interatrial septum can also help with the assessment of left and right atrial pressure. Volumetric measurements are most accurate. Mrs P: LA Volume = 66.5mls. Conclusion = Enlarged Left Atrium. (Image 10 LA Volume) Image 10 4. VALVES: Assessment of each valve should be by structure and function. Structure is usually assessed by zoomed 2D images whereas assessment of valvular function requires Doppler interrogation of blood flow through the valve. Doppler interrogation requires excellent technical skills and off axis measurements (misaligned Doppler cursor) can significantly underestimate trans-valvular gradients. Reference ranges for all measurements can be found on the BSE smartphone app. Tricuspid & Pulmonary Valves - TR and PR are usually assessed by eyeballing the colour Doppler regurgitant jet. Mild TR and PR is of no clinical significance. Severe TR causes flow reversal in the hepatic veins. Both tricuspid and pulmonary stenosis is rare but trans-valvular gradients can be measured. In general qualitative comments about the tricuspid and pulmonary valves are sufficient. Mrs P: Structurally normal tricuspid valve with moderate regurgitation. Structurally normal pulmonary valve with no regurgitation.
Aortic Valve (AV) - Significant aortic stenosis is usually diagnosed by the appearance of calcified and restricted leaflets on Para-sternal long axis (PLAX) and Parasternal Short Axis (PSAX) views (Video 7 PLAX Aortic Stenosis & Video 8 PSAX Aortic Stenosis. Both videos are provided as examples but are not relevant to the case of Mrs P). The continuity equation is the most accurate method of estimating aortic valve area and is given by the equation below. Extremely accurate measurements from the Left Ventricular Outflow Tract (LVOT) are required. It is assumed that the LVOT is a circle and therefore LVOT area is simply calculated using the formula πr 2. Importantly small errors measuring the LVOT diameter or radius are magnified because the value is then subsequently squared in the calculation. Velocity Time Integrals (VTI) are usually calculated automatically by standard software installed on most ultrasound machines. Aortic Valve Area = (LVOT VTI x LVOT Area)/Aortic Valve VTI (Images 11 LVOT Diameter, Image 12 LVOT VTI, Image 13 AV VTI. These images are provided as examples but are not relevant to the case of Mrs P). Pressure gradients across a stenotic valve are also used to grade severity but they are more prone to error and can be affected by other factors such as LV systolic function. Interested students are directed to the ESC guidelines (link provided). Aortic regurgitation is assessed by a combination of methods including colour and spectral Doppler. Mrs P: No measurements needed as valve normal. Only a qualitative comment Structurally normal trileaflet valve with no significant regurgitation Image 11
Image 12 Mitral Valve - Mitral stenosis is 99% rheumatic in aetiology and the valve has a characteristic hockey stick appearance on PLAX view. Mitral valve area is best calculated by tracing around the open valve leaflets in a PSAX view (planimetry) but information derived from Doppler interrogation is also useful. Mitral regurgitation (Video 9 - MR) is the most difficult of valvular lesions to accurately assess and interrogation from all parasternal and apical views in required. The most accurate way to quantify MR is by calculating regurgitant volume from measurement of Proximal Isovelocity Surface Area (PISA) on colour Doppler (Image 13- PISA). The aetiology of MR should always be stated and can be divided into organic or functional causes. Mild MR is of no clinical significance. Interested students are again directed to the ESC guidelines (link provided) Mrs P: MR Regurgitant Volume PISA = 43.9mls. Conclusion = Moderate functional MR AORTA, PERICARDIUM & OTHER FINDINGS: The aorta can be assessed at many points (ascending, arch, descending) using TTE. Standard measurements include the width at the level of aortic sinuses. Pericardial effusions are measured at end diastole and quantified as small, moderate or large however, size is less important than whether there are any echocardiographic signs of hemodynamic compromise as a result of the pericardial effusion. https://www.youtube.com/watch?v=eczqig--5oq
Image 13 Many additional findings can be identified on TTE including non-cardiac pathology such as pleural effusions and abdominal aortic aneurysms. SIGNIFICANT FINDINGS ON PERIOPERATIVE TTE In patients scheduled for non-cardiac surgery it is also helpful to consider the question of what constitutes a significant finding on preoperative resting TTE. Significant findings can be considered as those which affect perioperative risk stratification, alter clinical (medical, anaesthetic or surgical) management and at the extreme end of the scale those findings which lead to cardiac surgical intervention prior to undergoing non-cardiac surgery. Left ventricular (LV) systolic heart failure is considered a risk factor for adverse perioperative cardiac events and is a component of several clinical risk indices. Kazmers et al. (1988) found an LV ejection fraction (EF) of less than 35% to be the most accurate predictor of adverse perioperative events and this was confirmed by Hammill et al. (2008). Matyal et al. (2009) showed that diastolic dysfunction was an independent risk factor for perioperative congestive heart failure in a study of 313 high risk patients undergoing vascular surgery. However, more research is certainly needed in this particular area. Diastolic dysfunction is often not assessed preoperatively and does not feature on any commonly utilized clinical risk indices and may be an evolving pathology that we will begin to understand better in the future.
With regards to valvular function it is helpful to consider stenotic and regurgitant pathology separately with stenotic pathology being more poorly tolerated by patients undergoing non- cardiac surgery. The ACC/AHA considers severe stenotic valvular disease (AS with a valve area of <1 sq cm and symptomatic mitral stenosis (MS)) as one of four active cardiac conditions that require evaluation and treatment prior to non-cardiac surgery. The issue with regards to valvular regurgitation in patients undergoing non-cardiac surgery is more complex. The ESC/ESA guidelines (Dalby Kristensen et al. 2014) advise that asymptomatic patients with preserved LV systolic function and severe mitral regurgitation (MR) or aortic regurgitation (AR) are not at increased perioperative risk. The 2014 ACC/AHA Valvular Heart Disease Guidelines (Nishimura et al. 2014) state that it is reasonable to perform moderate risk non-cardiac surgery, with appropriate haemodymanic monitoring, on patients with asymptomatic severe MR and asymptomatic severe AR if EF% is preserved. Although it may be reasonable to proceed with surgery in these cases prior diagnosis and accurate quantification of valvular regurgitation is clearly essential for perioperative planning. In addition there will be many other factors that determine how an individual patient is managed. Pulmonary hypertension (PHT) is another area of uncertainty with most evidence coming from observational data of patients with pulmonary arterial hypertension (Type 1 PHT). However, complication rates are extremely high in this group with significant perioperative morbidity and mortality. Both the ESC/ESA and ACC/AHA make a number of recommendations regarding the perioperative management of patients with PHT including thorough evaluation and optimisation by a PHT specialist prior to surgery. It is known that elevations in right atrial pressure (RAP) and reduced cardiac output are more important than isolated elevations in right ventricular systolic pressure (RVSP) as the former are representative of right ventricular (RV) failure. An RVSP >70mmHg has, nevertheless been identified as a risk factor for adverse perioperative events (Minai et al. 2014). It is extremely unlikely there will ever be any studies looking at major incidental findings such as intra-cardiac mass or pericardial effusion on preoperative resting TTE however, it would seem logical to consider these findings significant. The challenge of interpreting a preoperative resting TTE is separating the wood from the trees. The clinician needs to extract all the relevant findings whilst not attaching significance to minor and irrelevant abnormalities such as PASP of 40mmHg in an obese patient or Type 1 diastolic dysfunction in an elderly man. Correct interpretation comes with experience and by studying a large number of TTE reports, seeking advice when necessary from experts in the field. A note regarding the links below Links 1 and 2 are included to give the reader an idea of the complex nature of a diagnostic TTE. Link 3 gives reference ranges for all TTE data (it is not expected this information is committed to memory). Some of the articles referenced in the discussion are also outside the scope of MSc Perioperative Medicine and provided for interest only.
Key links: 1 - https://www.youtube.com/watch?v=nuvf-rxezbe, 2 - http://www.bsecho.org/tte-minimum-dataset/ 3 - http://www.bsecho.org/bse-app/
Appendices: Table 1: Indications for Preoperative Resting TTE as per AHA/ACC, ESC/ESA & BSE Indication Patients with shortness of breath (SOB) of unknown origin Heart failure with worsening SOB or other change in clinical state Patients with clinically suspected moderate or greater degrees of valvular stenosis or regurgitation if a/no prior TTE in 1 year or b/significant clinical change since last study. Systolic murmur suggestive of AS Clinical history or physical examination suggests valvular disease Estimate pulmonary artery systolic pressure (PASP) Patients undergoing high risk surgery All patients with known or suspected Valvular Heart Disease, who are scheduled for elective intermediate or high risk, non-cardiac surgery. Ischaemic heart disease & Exercise tolerance < 4 metabolic equivalents (METS) SOB in absence of clinical signs of heart failure. Electrocardiogram (ECG) +/- Chest X-Ray (CXR) abnormal) Heart murmur & cardiac or respiratory symptoms Presence of heart murmur in asymptomatic patient who has clinically suspected severe structural heart disease. Class of Level of Organisation Recommendation Evidence recommending Class IIa Level C AHA/ACC Class IIa Level C AHA/ACC Class I Level C AHA/ACC Appropriate Helpful AHA/ACC AHA/ACC Useful in AHA/ACC perioperative planning Class IIb Level C ESC/ESA Class I Level C ESC/ESA BSE BSE BSE BSE
Table 2: Most Useful Measurements on a TTE Report Structure Left Ventricle Size Left Ventricle Wall Thickness Left Ventricle Systolic Function Left Ventricle Diastolic Function Right Ventricle Systolic Function Left Atrium Right Atrium Aorta Pericardium IVC Valves Aortic Stenosis Aortic Regurgitation Mitral Stenosis Mitral Regurgitation Tricuspid Regurgitation Pulmonary Stenosis Measurement Left Ventricular End Diastolic Diameter (PLAX) LV Interventricular Septum (PLAX) LV Posterior Wall (PLAX) LV Ejection Fraction MOD BP E/E, LA Volume TAPSE RV S LA Volume RA Volume Aorta at Sinuses (+other locations) Size of Pericardial Effusion Size and Collapsibility (to estimate RAP) AV Peak Velocity & Gradient AV Mean Gradient AV Area Cont Eqn (VTI) AI Pressure Half Time AI Vena Contracta Mitral Valve Area (Planimetry) Pressure Half Time MV Mean Gradient Regurgitant Volume (PISA) TR Peak Velocity (to estimate RVSP/PASP) PV Peak velocity
References: Hammill, B.G. et al., 2008. Impact of heart failure on patients undergoing major noncardiac surgery. Anesthesiology, 108(4), pp.559 567. Heyburn, G. & McBrien, M.E., 2012. Pre-operative echocardiography for hip fractures: time to make it a standard of care. Anaesthesia, 67(11), pp.1189 1193. Kazmers, A. et al., 1988. Perioperative and late outcome in patients with left ventricular ejection fraction of 35% or less who require major vascular surgery. J Vasc Surg. 1988 Sep;8(3):307-15 Matyal, R. et al., 2009. Perioperative diastolic dysfunction during vascular surgery and its association with postoperative outcome. Journal of vascular surgery, 50(1), pp.70 76. Minai, O.A. et al., 2013. Perioperative risk and management in patients with pulmonary hypertension. Chest, 144(1), pp.329 340. Nishimura et al., 2014. 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease. JAC, 63(22), pp.e57 e185. Wijeysundera, D.N. et al., 2011. Association of echocardiography before major elective non-cardiac surgery with postoperative survival and length of hospital stay: population based cohort study. BMJ, 342(jun30 1), pp.d3695 d3695.