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Non-invasive imaging
Setting up a stress echo service: best practice
  1. Mathivathana Indrajith,
  2. Madalina Garbi,
  3. Mark J Monaghan
  1. Cardiac Non-Invasive Diagnostics Department, King's College Hospital NHS Foundation Trust, London, UK
  1. Correspondence to Professor Mark J Monaghan, King's College Hospital NHS Foundation Trust, London, SE5 9RS, UK; mark.monaghan{at}nhs.net

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Learning objectives

  • Understanding the process of stress echo service development and the influencing factors.

  • Learning the requirements of a stress echo service.

  • Acknowledging the recommendations and guidelines underpinning a stress echo service.

Introduction

Stress echocardiography (SE) is well established in the assessment of ischaemic heart disease (IHD),1 ,2 and is used to detect ischaemia due both to epicardial coronary disease and microvascular disease. Furthermore, SE has an evolving role in the assessment of non-IHDs such as cardiomyopathies, valvular heart disease, pulmonary hypertension, heart transplant, congenital heart disease and athlete's heart.3 To rise up to the challenge of assessing more than only regional wall motion abnormalities (RWMAs), all echocardiographic techniques, both old and new, are currently used in SE (M-mode, two-dimensional (2D), pulsed, continuous and colour Doppler, lung ultrasound, 3D echo, 2D speckle tracking and myocardial contrast echo). The SE protocol is adapted according to the indication and for each particular case.3

There is a wealth of evidence regarding the diagnostic value of SE in IHD and in support of the evolving indications.1–9 Furthermore, there are guidelines, recommendations and appropriateness criteria regarding stress echo clinical indications and the procedure itself.2 ,4 ,5 ,6 ,8 However, there is limited literature to consult when developing a stress echo service; therefore, we compiled this guide in order to fill in this literature gap.6

When developing a new service, we have to take into consideration demand, capacity, competing techniques, commissioning, local policy for accepted indications, contraindications, and management of complications, types of stress echo to be performed, required space, equipment, consumables and staffing, reporting, audit and potential research.

The demand depends on the population covered, the guidelines followed, the agreed referral pathways, the agreed accepted indications and the coexistence of services providing an alternative functional test. The capacity is influenced by the available space, equipment and trained staff. The latter issue is an important limiting factor, especially in the UK. Consequently, a smaller service, generating a lower income, will have less ability to maintain a stable capacity over time when compared with a bigger service with a large number of trained employees. Predicted demand and capacity needs will have to be estimated and will represent the base of the business case.

Commissioning depends on local rules and regulations and it obviously has to be agreed before commencing the service, in order to ensure sustainability. However, the cost-effectiveness, ease of availability and lack of radiation of stress echo, when compared with other functional tests, have resulted in a significant growth in the technique.2 ,4 ,10

The local policy will be developed based on the expertise of the clinical lead, the expected demand, the range of indications agreed to be covered, the hospital settings, and the availability of coronary angiography and revascularisation onsite when necessary.

Specifications regarding the characteristics of the necessary space (outlined below) are likely to be defined by relevant professional bodies; for example the British Society of Echocardiography (BSE) and European Association of Cardiovascular imaging (EACVI) require certain specifications in order to award accreditation.5 ,6 Table 1 presents room specification, stress echo service equipment and consumable requirements, which are detailed later within the text.

Table 1

Specific requirements for stress echocardiogram service

An appropriately trained cardiologist should run the test. In the case of pharmacological stress echo, the presence of an adequately trained nurse is desirable.6 The scanning can be performed by the cardiologist or by a physiologist. All staff involved in SE should have up-to-date training in basic life support and advanced life support (ALS). For some clinical indications, depending on local policy and availability of appropriate training and expertise, the test can be physiologist-delivered or it can be delivered by senior cardiology imaging trainees with sufficient experience.11

Stress echo clinical indications

Ischaemic heart disease (coronary artery disease)

Several non-invasive modalities with reasonable diagnostic power as well as risk stratification of patients are used in the assessment and management of coronary artery disease (CAD).12 The choice of modality relies upon the local expertise and availability as well as upon the clinical indication for the test. Both exercise and pharmacological SE can be used in the assessment of IHD with equal diagnostic yield as other non-invasive functional imaging modalities (table 2).

Table 2

The clinical indications for the use of stress echocardiography in ischaemic heart disease

Since introduction in the 1980s, SE has evolved to become a cost-effective and safe method for diagnosis, risk stratification and management of patients with IHD.2 The introduction of contrast echocardiography has enhanced accuracy of detection of RWMAs.

Non-ischaemic heart disease (non-CAD)

SE has an evolving role in cardiovascular conditions beyond IHD as shown in table 3.3 ,9

Table 3

The clinical indications for stress echocardiography use in non-ischaemic heart disease

Types of stress

The types of stress echo provided by a service can be classified per clinical indication or per type of stressor used (table 4). For example, some stress echo services perform stress echo for CAD indications but not for non-CAD indications, or they can perform exercise stress echo but not pharmacological stress echo. The stressor used for SE can be physical exercise, a pharmacological agent or a combination of pharmacological agents, or a combination of dobutamine and electrical stress in patients with a permanent pacemaker.4

Table 4

Types of stress echocardiography and indication for use

Exercise SE

Exercise stress testing using a treadmill or a bicycle ergometer provides a physiological assessment and is the test of choice in many indications when feasible and when the patient is able to exercise.5 ,12 Furthermore, for some indications one can only use exercise (eg, assessment of mitral regurgitation) or to obtain information regarding certain parameters (eg, pulmonary pressure). Supine bicycle exercise testing provides the advantage of image acquisition at peak rather than post-peak test and even continuous image acquisition when needed. It is the exercise modality of choice in non-IHD indications and for assessment of contractile reserve.

Pharmacological stress test

Pharmacological stress is used in patients unable to exercise and those with known CAD who have resting RWMAs.

High-dose dobutamine SE is used to diagnose inducible ischaemia. Low-dose dobutamine SE is used to diagnose viability, the severity of aortic stenosis in low-flow aortic stenosis and the severity of mitral stenosis in native or prosthetic valves.5 ,9

Vasodilator SE, using dipyridamole or adenosine infusions, may also be used to diagnose inducible ischaemia. The sensitivity of the test is lower than with dobutamine. Thus, for higher sensitivity, use high-dose dipyridamole with atropine for RWMAs and low-dose dipyridamole where perfusion is assessed. The test duration is shorter because only baseline and peak (hyperaemia) image acquisitions are required.5

Electrically aided stress testing: pacing

In most pacemaker patients, exercise, dobutamine and vasodilator SE are possible. However, adjustment of pacemaker settings to complement dobutamine stress echo or indeed exercise stress echo may be needed if target heart rate cannot be achieved with stress alone.5 Elevating heart rate with pacing alone will only cause chronotropic stress. To induce inotropic stress as well, preferentially do a routine stress test with the opportunity to boost to target heart rate with pacing if required.

Contrast use

Contrast is used to improve endocardial delineation when two or more continuous myocardial segments are not well visualised on standard harmonic imaging. Following the European Society of Cardiology (ESC)/BSE recommendations13 contrast is used to enhance detection of RWMAs13 ,14 and it can be used to assess myocardial perfusion.15 ,16

It is prudent to be aware of the contraindications for SE as shown in box 1.

Box 1

Contraindications for stress echocardiography4,5

Absolute CI for all SE

▸ Acute coronary syndrome

▸ Left ventricular failure with symptoms at rest

▸ Life-threatening arrhythmias

▸ Severe left ventricular outflow obstruction and severe AS (except low-flow, low-gradient subgroup DSE can be considered)

▸ Severe systemic hypertension

▸ Recent pulmonary thromboembolism or pulmonary infarction

▸ Recent thrombophlebitis or active deep vein thrombosis

▸ Active endocarditis, myocarditis and pericarditis

▸ Electrolyte imbalance (hypokalaemia)

▸ Anaemia with haemoglobin <10 g/dL

▸ Hypervolaemia/hypovolaemia (eg, renal dialysis patients)

▸ High-degree heart block without pacemaker

▸ Inability to consent

▸ Atropine use in closed-angle glaucoma patients

▸ Poor echocardiographic windows despite administration of contrast

Absolute CI for ESE

▸ Bundle branch block or repolarisation abnormalities when ESE is performed for first diagnosis of ischaemia

▸ Unable to exercise

Absolute CI for vasodilator SE

▸ Suspected or known severe bronchospasm

▸ Second-degree or third-degree atrioventricular block with no PPM

▸ Sick sinus syndrome without PPM

▸ Hypotension

▸ Xanthine use in last 12 hours

▸ Dipyridamole in last 24 hours

Relative CI

▸ Sinus bradycardia

▸ Hypertrophic obstructive cardiomyopathy

▸ LMS stenosis if equivocal in coronary angiography

▸ Cerebral ischaemia/infarction

CI, contraindications; ESE, exercise stress echocardiogram; LMS, left main stem; PPM, permanent pacemaker; SE, stress echocardiography.

The SE service set-up

Stress echo room

BSE and EACVI departmental accreditation requires that the stress echo is performed in a room measuring at least 25 m2,5 ,6 thus sufficiently large to accommodate exercise equipment, echocardiography machine as well as the echocardiography bed, while maintaining walking areas and access to the patient. The room should have good ventilation and, ideally, air-conditioning, particularly if used for exercise echocardiography and in a warmer climate. A curtained area for patient preparation and privacy is useful.17

For SE, access to patient from both sides and easy access to the patient's head have to be ensured by placing the bed at sufficient distance from the walls of the room (figure 1). Monitoring devices and pumps have to be placed opposite to the patient scanning side (left if right-hand scanning).

Figure 1

Example of DSE room.

For treadmill exercise stress echocardiogram, we should ensure the shortest distance from treadmill to bed to allow fast transition without removing the electrodes at the end of the stress test (figure 2). This is because poststress, RWMAs can resolve within 60 s and thus can be missed. For supine bicycle exercise echo, the supine bicycle is positioned on the left side of the echo machine, as usually left-handed scanning is preferable.

Figure 2

Example of exercise stress echocardiogram room.

A time slot of 1 hour should be allocated for SE, to allow for patient preparation, performing the test, patient recovery and reporting. The existence of a recovery area is desirable, to allow patients to recover after the test, for 45 min. The intravenous cannula should not be removed during this period if contrast was used for the test, to allow quick access in case of a late contrast reaction.

The room has to have oxygen and suction facilities, a cardiac arrest trolley with appropriate equipment, necessary cardiac drugs, ECG, blood pressure and oxygen saturation monitors (figure 3).

Figure 3

Resuscitation trolley with necessary drugs and equipment.

A dedicated pump is needed for (SonoVue) echocardiographic contrast infusion. A fridge and dedicated agitation or infusion pump are needed for Optison echocardiographic contrast. Other contrast agents may have specific administration requirements and these should obviously be adhered to as prescribed by the manufacturer. In preparation for the rare event of a cardiac arrest, the room should be equipped with cord/bell for alerting the cardiac arrest team.

Equipment

Echocardiography machine

For SE the optimal visualisation of the endocardial border and of the myocardium is paramount. An appropriate, contemporary echocardiographic scanner with both tissue harmonic imaging and a contrast-specific imaging modality is essential. Doppler myocardial imaging, speckle tracking, 3D echocardiography and coronary flow settings are also desirable as there is evidence of added diagnostic value of these techniques to the standard 2D SE eyeballing of regional wall motion.

Image acquisition templates should be created on the machine, starting with apical views and leaving parasternal views at the end. Having the same routine in all cases helps performance. Starting with apical views is important when contrast is used, particularly in the case of bolus administration. This is because initially the quality of images is poor in parasternal views due to shadowing of the left ventricle by the high concentration of contrast in the right ventricle, which is interposed in between transducer and left ventricle in parasternal views. Furthermore, in exercise echo, parasternal views are unreliable during or postexercise due to fast and deep breathing. Parasternal views are therefore of secondary significance for contrast studies and even more so for exercise echo.

Image acquisition templates are mainly used for ischaemia or viability SE. However, they can be developed for all clinical indications, to act as a reminder throughout the test. They can be though restrictive in case of abrupt termination of the test. The operator should be always familiar with the process of template creation or editing for the echocardiography machine used.

Stress echo settings are essential, with the use of digital image acquisition and split or ‘quad-screen’ displays, to allow side-by-side comparison of rest and stress images in the same echo views.5 ‘Quad-screen’ analysis facilitates diagnosis and should be always available. Furthermore, the stress echo settings should include ‘smart stress’ ability (or equivalent), which automatically reproduces baseline settings in the same view throughout the test.

Workstations and electronic archive systems

Workstations are desirable for offline diagnosis and reporting (figure 4). The tests should be archived for governance, medico-legal, audit and research purposes. Electronic archive systems are desirable; in their absence, the tests can be saved on CDs or external hard-drives if the local confidentiality policy allows.

Figure 4

Reporting workstation with Quad screen display.

Exercise equipment

Treadmill

All medical treadmill systems have standardised specifications and have the ability to run according to a preprogrammed protocol.17 Most treadmill-exercise stress echo studies are performed with the Bruce or Modified Bruce protocol with some using Naughton protocol as required.

Bicycle ergometer

Bicycle ergometer is an alternative stressor for patients unable to use a treadmill. Furthermore, supine bicycle exercise is used when continuous image acquisition is required and it is the preferred method for exercise valve SE. Work intensity can be adjusted by varying the resistance and cycling rate. Work rate can be calculated in watts or kilopond-metres per minute (kept/min).

Two types of stationary bicycles are used for testing: mechanically braked and electronically braked. Mechanically braked ergometers require that a specified cycling rate be maintained, to keep the work rate constant. Electronically braked ergometers are more expensive and less portable but automatically adjust internal resistance to maintain specified work rates according to the cycling rate. These have become the standard for clinical testing when a cycle ergometer is used. Regardless of the type of stationary bicycle used, the ergometer must have the capability to adjust the work rate in increments either automatically or manually. They can be upright or supine.

The cycle ergometer should have handlebars and a seat that adjusts for height. For safety purposes, adaptable pedal grips should be included. In addition, meters, dials or digital displays should be appropriately sized and placed for easy reading. Additional equipment required are described in table 5.

Table 5

Other equipment required in a standard stress echo room

Drugs

A series of drugs have to be readily available in the stress echo room, locked away in drug cabinet between sessions as shown in table 6.

Table 6

Drugs required during stress echocardiography5

Staff and training

The structure of the stress echo team varies in between hospitals according to local availability of staff. The BSE and EACVI recommend the presence of at least two members of staff, one of whom is a clinician and one of them must be ALS trained or equivalent.5 ,6

Imaging cardiologist

Able to carry out the procedure independently and report unsupervised (level III) having performed and interpreted a minimum of 100 studies under supervision during training is the current American Society of Echocardiography (ASE), BSE and EACVI recommendation.5 ,6 Even if not scanning every patient, the imaging cardiologist should be able to scan during a stress echo and should have complete knowledge of the echo machine settings, pitfalls and troubleshooting.

Cardiac physiologist/sonographer

BSE or EACVI accreditation or similar certification is required. Although there is no standardisation for SE imaging, adequate training is required and it is the most demanding of all echo techniques.

Echo nurse

EACVI recommend nurse support.6 Nurse support is desirable especially when the cardiologists may scan by themselves. Coming from a cardiology nursing background coronary care unit (CCU, Cath lab, Cardiac Ward, and so on). The essential skills are cannulation, drug preparation and drug administration. The echo nurse will be in charge of the consumables needed. She/he will prepare the drugs for the list, will prepare the patients before the test, recover the patients after the test and discharge them. In a high-workflow department, the nurse can preassess selected cases, improving service efficiency by reducing cancellations.

Reception/secretary

Books appointments, sends out appointment letters, greets patients on arrival and sends out the reports to the referrer.

Necessary documentation

Patient appointment letters including advice on preparation for the test and information regarding the procedure have to be generated before opening the SE service. The BSE provides readily available patient information and informed consent forms, which can be downloaded from their website. Written or witnessed verbal consent should be obtained in every case before commencing the test.

Escalation protocols for management of complications and of the patients with severely abnormal tests should be generated, making them available in the department in easy-to-use diagrams.

Centres performing stress echo must have accomplished all the minimal standards at the basic level in transthoracic examination as well as meeting additional criteria as per EACVI as listed below. Departmental stress echo accreditation is being developed or enhanced by many national societies as well as international societies such as EACVI.

All stress echo services should aim for accreditation in order to benchmark their services and have an independent validation of quality of service. EACVI accreditation update published in 2014 includes both basic and advanced standard criteria for rating SE service.6 Quality control is ensured by regular auditing and comparison of results with other techniques (coronary angiography/CTCA) and performing outcome studies to check accuracy of the tests.

Demand and capacity

Strategic overview and local consensus for developing a stress echo service

The imaging report from the UK national cardiac imaging board published in 201018 ,19 states that out of 119 954 patients having had a coronary angiogram performed in 2008–2009, 71 000 were not subsequently referred for revascularisation, which suggests that they did not have obstructive coronary disease. This made the case for an increase in provision of functional imaging to avoid unnecessary angiography and also to inform subsequent revascularisation, substantially increasing stress echo demand. SE, or an alternative form of equivalent functional imaging, is offered to patients with new onset of chest pain at intermediate risk of having CAD based on 2003 National Institute for Health and Care Excellence guidelines risk stratification recommendations.10 ,20

The demand for SE is also influenced by the waiting time restrictions for diagnostic imaging, which were imposed by the 2004 NHS improvement plan and are <6 weeks for routine tests and 1 week for urgent tests. The diagnosis of patients with new-onset chest pain should be ideally completed within 2 weeks.

The capacity is limited by multiple factors including the length of the SE slots, the availability of adequate room and of the necessary equipment, the availability of trained staff and the volume of workload commissioned.

The business case for SE

As for every new service developed within a hospital, the identification in the lack of service provision drives the need for an SE service development proposal or a business plan. This has to be submitted and considered by the appropriate local authority in all types of healthcare systems. It will have to describe the way the service will fit within the broader service and will meet demand in accordance with standards. It will have to include plans for appraisal and audit, referral pathways and financial considerations regarding commissioning, income and costs.

Financial considerations

Income and cost

The income will depend on national and local agreed prices and on commissioning pathways. It will be influenced by the volume of the service and by the impact of the service on other services within the hospital. For example, external referrals may consider referring patients with a positive test within the same hospital for invasive investigation and management.

The number of tests performed will influence the total cost of providing the test, by summing up the cost of individual tests but also by reducing the cost of purchased consumables for an individual test. The total cost comprises cost of estates and facilities, equipment purchase and maintenance cost. Where alternative functional imaging services already exist in the hospital, the impact on these services has to be considered within the overall cost.10 ,21

Equipment purchase

Depending on local healthcare system regulations, the selection of the equipment to purchase may be based on preference of the SE team or on a formal purchase tender process. A formal tender process is used in the NHS, advertising the intention towards existing providers and selecting the most practical and affordable item based on the recommendation from the SE service lead and review and approval by the NHS Trust Board.

Future perspectives

SE applications continue to evolve, based on advances in technology and techniques such as 3D SE. Consequently, a stress echo service will need to adapt to changes, increasing capacity to accommodate an increase in demand, and ensuring training of the staff involved and implementation of new applications.

Conclusion

The versatility, wide availability, low cost and lack of radiation encourage the use of SE in clinical practice. The development of a stress echo service should take into consideration the demand for service, local expertise, resources, necessary equipment and adequate staffing for its efficient application. Funding of the development process and commissioning of the service have to be ensured. This review provides guidance for setting up a new service or expanding an existing one.

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References

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Footnotes

  • Contributors All authors have contributed equally to writing this article.

  • Competing interests None declared.

  • Provenance and peer review Commissioned; externally peer reviewed.

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