A commonly used test involving a treadmill, blood pressure (BP) measurement, and continuous electrocardiograph (ECG) monitoring. Overall sensitivity for coronary heart disease is around 68% and specificity is 77%. This increases when considering prognostically significant disease, which has a sensitivity of 86%. The test improves to have a predictive accuracy of >90% in intermediate- to high-risk patients (older men with ischaemic symptoms). The test is of least value in populations that are least likely to be suffering from ischaemic heart disease; e.g. asymptomatic middle-aged women have a positive predictive value of <50%.

Indications

• Diagnosis of ischaemic heart disease (IHD): intermediate- or high-probability IHD, vasospastic angina.

• Post-myocardial infarction (MI): pre-discharge (submaximal test in days 4–7 to assess prognosis, decide upon exercise programme, and evaluate treatment), late post-discharge (symptom-limited 3–6 weeks).

• Pre- and post-revascularization.

• Evaluation of arrhythmias: optimizing rate-responsive pacemaker function, evaluation of known or suspected exercise-induced arrhythmias, and evaluation of treatment of above.

Contraindications

• Fever/acute viral illness.

• Myocarditis/pericarditis.

• Severe aortic stenosis.

• Aortic dissection.

• Uncontrolled hypertension.

• Overt cardiac failure.

• Unstable angina or acute phase of MI.

• Significant resting arrhythmia (e.g. uncontrolled atrial fibrillation or complete heart block).

• Known severe left main stem (LMS) or LMS equivalent disease.

• Physical disability.

• ECG abnormality rendering interpretation of ST segment difficult (e.g. left bundle branch block (LBBB), left ventricular hyphetrophy (LVH) with strain or digoxin ECG changes).

When to stop

• Target heart rate achieved (tests have better sensitivity and specificity if the target heart rate is reached (>85% of 220 minus age in years for men or 210 minus age in years for women).

• Worsening angina or excessive breathlessness.

• Dizziness.

• Fatigue/patient requests to stop.

• Atrial arrhythmia other than ectopic beats.

• Frequent ventricular ectopic beats or ventricular tachycardia (VT).

• Worsening ST segment shift (elevation or depression) at least 2 mm depression but up to 5 mm depression.

• BP fall or failure to rise.

• Exaggerated hypertensive response to exercise (systolic blood pressure (SBP) >220 mmHg).

• New high-grade atrioventricular (AV) block or bundle branch block.

Criteria for a positive test

• Planar or downsloping ST depression of at least 1 mm 80 ms after the J point (junction between the QRS and ST segment).

• ST elevation.*

• Increase in QRS voltage (ischaemic left ventricular (LV) dilatation).

• Failure of BP to rise during exercise (ischaemic LV dysfunction).^*

• Ventricular arrhythmias.^*

• Typical ischaemic symptoms during exercise.

• Inability to increase heart rate.

*Features that are indications for urgent angiography: Also ST depression at low workload (<<6 minutes Bruce) in multiple lead groups, persisting into recovery, >2 mm, downsloping pattern.

Causes of false-positive tests

• Cardiomyopathies.

• Hypertension.

• LVOT (left ventricular outflow tract) obstruction.

• Mitral valve prolapse syndrome.

• Hyperventilation.

• Resting ECG abnormality (LBBB, pre-excitation, digoxin).

• Electrolyte abnormalities (hypokalaemia).

• Tricyclic antidepressants.

• Syndrome X.

• Coronary artery spasm.

• Sympathetic overactivity.

National Institute for Health and Clinical Excellence (NICE) guidance 2010—chest pain of recent onset 1

Historically, exercise ECG testing has been the cornerstone of investigation of patients presenting with stable anginal chest pain. However, sensitivity and specificity are poor compared with other investigations. Recent UK guidelines discouraged the use of exercise ECG in patients without known coronary artery disease.

Instead, NICE recommended cardiac computed tomography (CT) for patients with low likelihood of significant coronary artery disease, a functional test such as dobutamine or exercise echocardiography for those with intermediate likelihood, and invasive coronary angiography for those with high likelihood.

Cardiac computed tomography

In the past decade, major advances in CT technology have enabled cardiac CT to emerge as a non-invasive alternative to conventional invasive coronary angiography.

Coronary artery calcium scoring

Calcified coronary plaque represents approximately 20% of the total coronary artery plaque burden. Therefore, the degree of coronary calcification can be used as a surrogate for coronary artery atherosclerosis. A calcium score is obtained through a low-radiation unenhanced (i.e. no iodinated contrast) scan. The degree of calcification in each coronary vessel is then expressed as a figure and summed to give the total coronary artery calcium score, commonly using the Agatston scale. A score of 0 correlates with a low risk of coronary artery disease, whereas a score of >400 correlates with high risk of significant atherosclerotic plaque burden.

Clinical studies have shown that the calcium score provides additional information for cardiovascular risk stratification above and beyond traditional factors such as age, sex, hypertension, family history, hyperlipidaemia, and diabetes.

CT coronary angiography

CT coronary angiography is performed by injecting iodinated contrast into the peripheral veins. When the level of contrast in the aorta reaches a specified level, the scan is launched and images are acquired. The images are then analysed using computer software, which allows manipulation in two dimensions and three-dimensional (3D) reconstruction of the coronary arteries and cardiac chambers, also known as ‘volume rendering’.

Technical considerations

Temporal versus spatial resolution

The principal challenge to imaging the coronary arteries using CT is to achieve high temporal resolution. Temporal resolution is defined as the time taken to acquire an image. As the beating heart moves, it needs to be ‘frozen’ during image acquisition. Motion is greatest during systole, whereas the heart is relatively still during diastole. Images acquired during diastole are therefore most likely to be motion free, allowing accurate interpretation and diagnosis. A CT scanner must therefore be capable of acquiring images rapidly during the short diastolic phase when the heart is motionless.

Imaging small structures such as coronary arteries requires high spatial resolution. Spatial resolution is defined as the narrowest distance between two objects that can be distinguished by the detector. CT spatial resolution is determined by the voxel size (i.e. 3D pixel).

Heart-rate control

The duration of systole is relative fixed at different heart rates, but the duration of diastole varies greatly. A slow heart rate (i.e. <65 bpm (beats per minute)) is preferable, to ensure motion-free imaging of the coronary arteries.

Oral beta-blockade given 1–2 h before the scan is widely used in the United States. Alternatively, intravenous beta-blockade with serial boluses of metoprolol administered to the patient on the CT gantry has been shown to be a safe, fast, and effective method of achieving optimal heart-rate control. Premedication with two days of oral beta-blockers (to be taken the day before and on the day of the scan) is also effective and minimizes the need for administration of intravenous metoprolol at the time of the scan. Calcium-channel blockers are a practical alternative in patients with a contraindication to beta-blockers

Strategies for reducing radiation effective dose

A number of strategies have emerged to reduce the effective dose of ionizing radiation per scan:

• reduction of field of view (‘carina to base of heart’)

• tube voltage reduction in non-obese patients (from 120 kV down to 100 kV)

• electrocardiographically controlled tube current modulation (current is reduced in systole and increased in diastole)

• electrocardiographically controlled prospective gating (tube is only switched on at specific phase of the cardiac cycle, usually mid-diastole or 75% of the R–R interval).

By combining these techniques, the effective dose for CT coronary angiography is now approaching 1 mSv (milli-Sievert).

Sensitivity and specificity

Modern 64-slice and above CT scanners have been shown to provide excellent sensitivity (95%) and specificity (83%). As a consequence, CT coronary angiography has a very high negative predictive value (upwards of 95%). The principal clinical application of CT coronary angiography is to rule out significant coronary artery disease in patients with low to intermediate cardiovascular risk.

Clinical applications of cardiac CT

Comparison with traditional invasive coronary angiography

Traditional cardiac catheterization remains the gold standard for diagnosing coronary artery disease. It has excellent temporal and spatial resolution and allows for intervention if significant disease is identified. However, it is invasive and exposes the patient to potential vascular complications, including MI, stroke, and vascular-access complications.

With new 256- or 320-detector CT, the extended coverage and scan time of less than 0.5 s allows the entire heart to be imaged in a single heartbeat. Compared with conventional angiography, CT has a lower spatial resolution (0.4–0.6 mm vs. 0.2 mm) and temporal resolution (60–220 ms vs. 8 ms).

Comparison with functional tests

Historically, non-invasive functional tests (e.g. exercise tolerance testing, stress echocardiography, nuclear imaging, positron emission tomography (PET), perfusion magnetic resonance imaging (MRI)) have been used to select those patients deemed at intermediate risk who are likely to require invasive coronary angiography and intervention. However, many of these tests are labour intensive and not all are readily available in every hospital. In addition, the false-positive rate is substantial, leading to patients with normal coronary arteries undergoing unnecessary cardiac catheterizations.

Indications for cardiac CT

The principal role of cardiac CT in current clinical practice is to rule out or detect coronary artery disease. CT is particularly good at assessing anomalous coronary arteries and coronary artery bypass graft patency.

Additional indications

These include:

• screening for coronary artery disease (i.e. calcium scoring).

• detection of coronary artery disease in patients at low to intermediate risk.

• assessment of coronary artery bypass grafts (CABGs).

• assessment of anomalous coronary arteries.

• pulmonary vein mapping prior to electrophysiological studies/ablations.

• assessment of congenital heart disease anatomy.

• evaluation of intracoronary masses.

• evaluation of suspected aortic dissection.

• assessment of coronary stent patency.

• assessment of plaque morphology—soft/calcified/mixed.

Advantages and disadvantages of cardiac CT

Advantages

• Fast.

• Non-invasive (avoids vascular risks of invasive angiography).

• Inexpensive.

• Identifies CABG graft origin/target/patency.

• Plaque characterization—i.e. ability to assess not just the vessel lumen but also the vessel wall (soft/calcified/mixed morphology).

Disadvantages

• Ionizing radiation.

• Difficult to interpret degree of stenosis if there is significant coronary calcification.

• Difficult to see into stents and assess patency.

• Difficult to interpret degree of stenosis at CABG graft anastamosis.

• Requires regular and slow heart rates.

Future applications of cardiac CT

CT perfusion imaging

New CT techniques are now enabling integration of anatomical assessment of the coronary arteries with functional information. Intravenous contrast is injected and the myocardium is scanned repeatedly over a period of time. The first pass of contrast through a region of interest is tracked to produce tissue-specific time–density curves, which are then interpreted to determine blood flow within the tissue. However, using current CT technology, the predominant barrier to use of CT perfusion in routine clinical practice is high radiation doses.

Multimodality hybrid imaging

An alternative to CT perfusion imaging is integration of the anatomical information from CT angiography with the functional information from stress echocardiography, single photon emission computed tomography (SPECT), PET, or perfusion MRI. Clinical studies have shown that fusing functional and anatomical information increases the sensitivity and specificity when compared with each modality in isolation.

Transthoracic echocardiography

Introduction

Despite dramatic advances in new cardiac imaging technologies, echocardiography remains the most important diagnostic imaging tool in clinical practice. Since its development by Edler and Herz almost five decades ago, and routine clinical implementation a decade later, echocardiography has developed into an intuitive, comprehensible, and practical method to rapidly and repeatedly evaluate cardiac morphology and function. Competent interpretation of the echocardiographic examination first requires an understanding of the physical principles underlying the various technique modalities.

Ultrasound physics

All forms of ultrasonic imaging are based on generation of high-frequency (>1 MHz) acoustic pressure waves from a transducer comprising one or more piezoelectric crystals. Current is passed across the latter, leading to material deformation and wave transmission. The piezoelectric element also serves as a receiver, and waves returning from insonified objects (e.g. walls, valves) deform the crystal(s), which, in turn, generate a current that can be sampled over time. Because the velocity of sound is constant, object location (spatial resolution) can be determined based on the timing of the returning signal. The amplitude of the returning signal is based on the angle of incidence (surfaces perpendicular to the ultrasound beam are stronger reflectors) and the interface of acoustic impedances (greater differences such as occur in the left ventricle at the tissue–blood interface lead to greater reflectivity). Returning ultrasound information is processed for maximum image integrity and then mapped to pixels for display and storage. While many institutions continue to store images on videotape, image degradation necessarily incurred by this medium, as well as ease-of-use issues, have led to increased implementation of digital storage, primarily on dedicated file servers.

M-mode

This was the first available form of echocardiography and, while still available on modern machines, has largely disappeared from routine use in modern laboratories. M- or ‘motion’-mode images depict a single line of ultrasound over time (Fig. 1.1). The information is graphic in nature and requires considerable experience for accurate interpretation. Its advantage lies in its high sampling rate (>1 kHz) and resultant ability to depict rapidly moving structures that may be of interest from a didactic or physiological perspective.

Fig. 1.1 Normal M-mode echocardiogram (AV = aortic valve; HOCM = hypertrophic obstructive cardiomyopathy; VS = interventricular septum; LA = left atrium; LV = left ventricle; MV = mitral valve; PW = posterior wall of LV; RV = right ventricle). After R Hall. Med Int 17: 774. Reprinted with permission from Longmore M, Wilkinson I, Davidson E, Foulkes A, and Mafi A (2010). Oxford Handbook of Clinical Medicine. 8th ed. Oxford: Oxford University Press.

Two-dimensional (2D) or sector scanning (Fig. 1.2)

When an ultrasound beam is swept across a chosen cardiac window, rapid sequential sampling can be performed, leading to display of multiple ‘scan lines’ of information and a sector image created nearly instantaneously. Since a finite number of scan lines is possible, interpolation of data between lines is performed and an image slice or sector (hence the term ‘sector scanning’) is stored in digital form. Through reiterative acquisition over a cardiac cycle, a movie composed of sequentially acquired sectors is created, demonstrating structural motion, which can then be displayed on a monitor. Beam sweeping can be performed by mechanical rotation of one or more crystals, or through the use of programmed firing of a bank of crystals (phased array). Sampling rates were previously dictated and limited by videotape standards (e.g. PAL (phase alternating lines) or NTSC (National Television Standard Committee)) but, with digital capabilities appearing in some form on virtually all machines and replacing outdated tape technology, higher frame rates are possible.

Fig. 1.2 The so-called ‘anatomical position’. The subject is upright and facing the observer. Any structure within the body can be described within the references of the three orthogonal planes—two in the long axis and the third in the short axis. Reprinted with permission from Anderson RH, Ho SY, Brecker SJ (2001). Anatomic basis of cross-sectional echocardiography. Heart 85: 716–20.

The availability of harmonic tissue imaging has substantially improved image resolution by eliminating artefactual ‘noise’. Low-level signals emanating from tissue and comprising the first harmonic of the transmitted ultrasound are selectively sampled. In this way, extraneous reflections such as reverberations are filtered out, leaving a cleaner image.

Three-dimensional (3D) imaging (Fig. 1.3)

While two-dimensional (2D) ECHO presents user-selected sector or tomographic information, 3D ECHO has the potential to provide a comprehensive evaluation of cardiac anatomy similar to that of more quantitatively mature technologies such as MRI or CT. Three-dimensional ECHO can be performed using the ‘freehand’ approach, in which multiple 2D sectors are acquired from a probe that is positionally mapped using a ‘spark gap’ or magnetic tracking system. Both image and position data are stored for post-hoc 3D rendering. The development of rotational and, more recently, matrix array probes, coupled to powerful computer technology, has made post-hoc, 3D chamber reconstruction a reality, with accurate volumetric assessment. Most recently, real-time rendering of spatially limited cardiac segments has been made available. There are considerable limitations, and it is currently available in limited form from various manufacturers.

Fig. 1.3 The heart lies in the mediastinum with its own long axis tilted relative to the long axis of the body. Appreciation of this discrepancy is important in the setting of cross-sectional echocardiography. Reprinted with permission from Anderson RH, Ho SY, Brecker SJ (2001). Anatomic basis of cross-sectional echocardiography. Heart 85: 716–20.

Transthoracic Doppler imaging

Quantification of object motion within the heart is performed using Doppler-based technologies. In brief, the same equipment described earlier propagates ultrasound, which is aimed at moving red blood cells or tissue.

• The frequencies of returning ultrasound are shifted upwards and downwards by cells travelling towards and away from the transducer, respectively.

• The frequency shift is proportional to an object’s velocity.

• The signal intensity is dependent on the number of cells moving at a particular velocity.

• Velocity information is depicted graphically as a spectral pattern over time (similar to the M-mode display) or mapped to pixels as colour overlaying the 2D or 3D image.

• The ECHO beam must be as parallel as possible to the target, with off-axis angulation by >30° leading to significant underestimation of velocities.

Doppler is restricted in its ability to sample high velocities by the Nyquist limit, which is dependent on the sampling rate (the lower the frequency, the higher the evaluable velocity) and object depth (the deeper the object, the lower the sampling rate). When the frequency shift of moving objects (i.e. velocity) exceeds the Nyquist limit, aliasing occurs, precluding velocity assessment.

Pulsed Doppler permits accurate sampling of blood velocities averaged within a limited region of interest or ‘sample volume’. Transducer elements serve as both transmitters and receivers, permitting selective sampling of reflected ultrasound and accurate range or spatial information. Pulsed Doppler spectral displays portray velocity vectors over time:

• laminar flow is found within normal vessels and chambers and characterized by a gradual increase in flow velocities from the vessel wall to the vessel centre.

• laminar flow is characterized by a narrow spectral trace representing a relatively discrete population of blood velocities.

• turbulent flow occurs across stenotic or regurgitant orifices (valves, shunts, etc.), where high-pressure gradients lead to high red-cell kinetic energy and disordered, high-velocity motion.

• turbulent flow is graphically portrayed as spectral broadening.

• aliasing often occurs with high-velocity jets, leading to ‘wraparound’ or the ‘paint brush sign’.

Flow quantitation from pulsed Doppler

Quantitation: pulsed Doppler spectral traces can provide important information regarding flow quantitation or timing, e.g. assuming that sampling occurs at an orifice with a relatively fixed area over the cardiac cycle (e.g. the left ventricular outflow tract) by integrating the time–velocity spectral curve (‘time–velocity integral’ or TVI), the area under the curve can be multiplied by the area of the orifice (determined from 2D ECHO) and stroke volume determined.

Continuous wave (CW) Doppler involves continuous transmission of ultrasound with one transducer element, while a second element serves as a receiver. Higher sampling rates are achieved and, consequently, higher velocities, as found in stenotic and regurgitant lesions, can be measured. CW Doppler does not permit ranging information to be acquired and all velocities along a scan line are included in the spectral trace. CW Doppler can be performed with stand-alone (Pedoff) probes, where the operator determines sample location based on familiar spectral patterns.

Imaging CW Doppler permits beam steering. Transducer elements are shared for the purposes of CW and intermittent 2D imaging. A virtual cursor positioned over the 2D image can be moved to guide and minimize off-axis sampling angulation. CW Doppler velocities are depicted as a filled-in spectral tracing, since these represent sampling of all of the velocities in structures along the sampling cursor (or ultrasound beam). Blood cells travelling at the fastest velocities are represented at the outer edge of the spectral trace (peak) or darkest line of the trace (modal) velocities.

Colour Doppler flow imaging employs multigate pulsed Doppler to portray blood flow overlying the 2D image. Information is used to detect regurgitant or stenotic lesions or shunts, and qualitative assessment of velocities is possible using colour maps.

• Pixels are assigned a colour based on user-configurable mapping parameters. Pixel colour is based on average velocity in the pixel region of interest.

• By convention, the BART colour map system is used in all machines, with blue colours representing flow away from the transducer and red colour depicting flow towards the transducer (Fig. 1.4).

• The lighter the colour, the higher the velocity.

• Abnormal velocity distributions characteristic of turbulence can be mapped, usually by including a green hue (‘variance mapping’).

• Aliasing is depicted as a mix of colours or a ‘mosaic’ pattern.

Fig. 1.4 Colour Doppler (Red: toward flow; Blue: away flow). Reproduced with permission from Shanewise JS. Journal of the American Society Echocardiography 1999;12:884–900.

Tissue Doppler imaging (TDI) is used to assess low-velocity displacement of structures. A high-pass filter excludes higher-frequency shifts caused by red-cell flow, leaving only low-velocity shifts attributable to wall motion.

• Mitral or tricuspid annular motion can be tracked and correlates with systolic and relaxation performance of the associated ventricles.

• Regional wall motion can be assessed for displacement, which may be affected by overall cardiac motion or local tethering.

Strain rate imaging can measure regional thickening and thinning, independent of the external influences described above, which influence tissue Doppler measurements. With strain rate imaging, two sampling sites are simultaneously acquired and inter-sample displacement (strain) over time (strain rate) can be determined.

Calculations from Doppler measurements

Valve gradients. The velocity of blood cells travelling across a narrow orifice is directly proportional to the pressure gradient at that point in time. This relationship is approximated by the simplified Bernoulli formula:

In situations where there are high flow velocities (e.g. aortic stenosis with high LVOT velocities), the flow before the stenosis must be accounted for.

Both peak and mean gradients can be determined, the latter by integrating the velocity spectra over a cardiac cycle.

Valve area (continuity equation). This is based upon the principle that flow in the pre-valve area (e.g. LVOT) = flow across the valve. It is generally used for aortic stenosis quantitation, though it is applicable to other stenotic orifices as well.

As aortic valve flow = LVOT flow,

PLA = parasternal long axis.

The standard transthoracic ECHO

Most laboratories employ imaging protocols incorporating acquisition of images from standard windows, resulting in standard views presented in a fairly standard sequence. Image quality is maximized by avoiding pulmonary artefacts and rib reflections. Pulsed and colour flow Doppler are performed following 2D imaging in each view. Standard ECHO windows and views include:

Left parasternal window

• Long axis (PLA) (Fig. 1.5): left atrium, ventricle, proximal ascending aorta, mitral and aortic valves, and right ventricle.

• Short axis (PSA) (Fig. 1.5): four levels—aortic valve/left atrial level: includes the tricuspid and pulmonic valves and pulmonary artery; mitral valve, papillary muscle, and apex.

• Right ventricular inflow tract (RVIT).

• Right ventricular outflow tract (RVOT).

Fig. 1.5 (a) Parasternal long axis view; (b) Parasternal short axis view (aortic level). Reproduced with permission from Shanewise JS. Journal of the American Society Echocardiography 1999;12:884–900.

Apical window

• 4 chamber (A4Ch): atria, ventricles and AV valves, media, septal, and anterolateral LV walls.

• 5 chamber (A5Ch): A4Ch angled anteriorly to the LVOT.

• 2 chamber (A2Ch): anterior and inferior LV walls.

• 3 chamber/apical long axis (A3Ch): apical version of PLA view with the anteroseptal, posterior walls, and LVOT.

• Suprasternal window (SS): aortic arch.

• Subcostal window (SC): 4 chamber, short axis, inferior vena cava.

• Suprasternal window (optional): aortic arch and proximal descending thoracic aorta.

• Right parasternal window (optional): ascending aorta and CW Doppler of the aortic valve.

Chamber evaluation

• Chambers are routinely measured from M-mode tracings or, preferably, using digital calipers to perform point-to-point (PTP) assessment from 2D images.

• Area tracings provide enhanced accuracy but are time-consuming.

• Volumes are derived from 2D and PTP analysis using geometric modelling. The most common volumetric approaches include the modified Simpson’s biplane method of stacked discs, bullet and area–length formulae.

• 3D volume assessment has been validated but the technology is immature and inappropriate for routine clinical assessment.

• Most clinical labs perform PTP measurements online. End-diastole is usually defined as the beginning of the QRS complex, and end-systolic measurements are performed at maximum LV contraction.

The standard transthoracic ECHO: continued

Left atrium

• Measure at ventricular end-systole (minimum LV chamber dimension).

• Linear (anteroposterior) from PLA view at aortic cusp level (A4Ch).

• Area (A4Ch) and volume (preferably modified Simpson’s formula).

Left ventricle

• Measure at end-diastole and end-systole.

• Linear from PLA at mitral tips in end-diastole/systole.

• Septal wall thickness from PLA at mitral tips in end-diastole.

• Posterior wall thickness.

• Volumes (modified Simpson’s biplane method of discs).

• Derived variables:

• fractional shortening: LVIDd–LVIDs/LVIDs where LVID = LV internal diameter in diastole (d) and systole (s).

• ejection fraction (from 2D- or 3D-generated volumes or derived from M-mode (e.g. Teicholz formula)).

• mass: can be derived from M-mode measures (American Society of Echocardiography (ASE)-modified Penn formula), 2D volumetric models, or 3D reconstruction. M-mode mass calculations tend to over-quantify LV mass.

Aortic root and ascending aorta

Linear measurements from 2D PLA view or M-mode. The root is measured at cuspal level, and the aorta is measured at the sinotubular junction and 2 cm above this.

Right atrium

• Area from 2D A4Ch view.

• Inferior/superior and lateral/medial PTP measurements.

Right ventricle

• PTP measurements are exclusively used.

• Irregularity of chamber configuration makes standardized quantitation difficult.

Pulmonary artery

PTP medial–lateral measurement in PSA at aortic valve level.

Assessment of wall motion

Assessment is based upon review of multiple cuts as described earlier. In general, abnormalities of LV regional function should be apparent in more than one view. Various labelling systems have been used but the American Heart Association (AHA) Cardiac Imaging Committee 17-segment model is the standard convention:

• basal (6): anteroseptal, anterior, anterolateral, posterolateral, inferior, inferoseptal.

• mid LV (6): same as above.

• apical (5): anterior, lateral inferior, septal, and true apical. See Fig. 1.7.

Fig. 1.6 (a) Parasternal long-axis view (RV inflow); (b) parasternal short-axis (mitral valve level); (c) apical 4-chamber view; (d) suprasternal long axis. Ao = aorta; IVC = inferior vena cava; Pa = pulmonary artery. Reproduced with permission from Shanewise JS. Journal of the American Society Echocardiography 1999;12:884–900.

Fig. 1.7 American Heart Association 17-segment model. From Swanton H (2003) Pocket Consultant: Cardiology. 5th ed, Oxford: Blackwell Publishing.

Regional functional assessment

• Systolic function should be classified as ‘normal’, ‘globally hypokinetic’, or demonstrating the presence of ‘regional wall motion abnormalities’.

• Global hypokinesis is consistent with cardiomyopathy, either ischaemic or non-ischaemic. Some degree of regional variation may be present in non-ischaemic cardiomyopathy.

• The presence of distinct regional wall motion abnormalities with large areas of normal regional function is suggestive of underlying coronary artery disease.

• Evaluation should ideally be based on the degree of regional thickening as opposed to endocardial motion. Unfortunately, this is not always possible.

• Each regional segment can be qualified as:

• Wall motion quantification, based on similar characteristics, may be prognostically useful, but is not useful in routine evaluation.

• Identification of hyper-echogenic, thinned areas suggests the presence of scarring and should be mentioned in the evaluation.

• Scarred segments may demonstrate endocardial motion, without wall thickening, due to tethering by peripheral segments.

Assessment of LV systolic function

Global functional assessment

• Ejection fraction estimation is usually performed qualitatively. Echocardiographers need to routinely ‘recalibrate’ their assessment abilities by comparing qualitative readings to more accurate quantitative modalities, such as MRI, radionuclide ventriculography, 3D or even quantitative 2D ECHO (see Table 1.1).

• 2D ECHO ejection fractions can be quantified most efficiently on or offline by the:

• Simpson’s modified biplane method of stacked discs: A4Ch and A2Ch LV traces are performed and the apex–annulus length is divided into a standard number of equal segments, the length of which serves as disc height. Cross-sectional disc area is calculated from the elliptical formula (πr₁r₂) where r₁ and r₂ = the endocardial medial–lateral dimension of each segment in the A4Ch and A2Ch views, respectively.

• cylinder hemi-ellipsoid model: volume is determined by measuring the LV endocardial area (A) on the PSA view at the papillary muscle level and the longest apex–annulus length (L) in any apical view. Volume = 5/6AL.

• LV stroke volume: integration of LVOT spectra × LVOT area (derived from diameter in PLA view).

• Systemic output: LV stroke volume × heart rate.

• Pulmonary stroke volume: integration of pulmonary artery spectral trace × pulmonary artery area (derived from systolic medial–lateral dimension at the level of Doppler sampling).

• RV output: pulmonary stroke voume × heart rate.

• Pulmonic/systemic shunt ratio (Qp/Qs): pulmonary output/systemic output.

• Tissue Doppler of mitral and tricuspid annular motion.

Table 1.1 Assessment of left ventricular ejection fraction

LV ejection fraction	Qualitative assessment
>75%	Hyperdynamic
55–75%	Normal
40–54%	Mildy reduced
30–39%	Moderately reduced
<30%	Severly reduced

Essential aspects of ECHO assessment in patients with impaired LV systolic function

Anatomy

• LV dimensions (systolic and end diastolic).

• LV ejection fraction.

• Regional wall motion abnormalities.

Doppler characteristics

• E:A ratio (grade according to Fig. 1.7 Assessment of LV diastolic function, p. 27).

• E deceleration time.

• Estimate pulmonary artery (PA) systolic (from tricuspid regurgitation (TR) jet).

• Estimate PA diastolic (from pulmonary regurgitation (PR) jet).

• Estimate pulmonary capacitance (= stroke volume/(PAs – PAd pressures)).

Implications for therapy

• Mitral regurgitation at end diastole if AV delay too long.

• Dys-synchrony (TDI septum/lateral annulus >60 ms).

Assessment of LV diastolic function

Evaluation of LV diastolic function includes measurement of the various phases of diastole including isovolumic relaxation, early filling, diastasis (atrioventricular pressure equilibration without LV filling), and atrial systole. These measures are generally age and heart-rate dependent, and affected by LV loading conditions to variable degrees (see Fig. 1.8).

Fig. 1.8 Echocardiographic classification of diastolic dysfunction. Reproduced with permission from Journal of the American College of Cardiology, Vol 48, No.3, 2006. August 1, 2006:e1–148. Bonow et al, AHA/ACC Best Practice Guidelines.

Pulsed Doppler mitral inflow: E wave (peak early diastolic velocity), A wave (peak atrial systolic velocity), E/A ratio and transmitral deceleration time. The following should be taken into account when assessing these parameters:

• E/A ratio is particularly dependent on sample volume placement (annulus, mitral tips, etc.) and loading conditions.

• E/A ratio decreases with age, and assessment must be age-normalized. An E/A ratio <1.0 is common among the elderly and often represents normal aging.

• increasing LV filling pressures (e.g. in heart failure) lead to ‘pseudonormalization’ of the ratio, which often reverts to an abnormal pattern following manoeuvres to reduce LV preload (e.g. diuresis) or Valsalva manoeuvre.

• the deceleration time correlates somewhat with invasive measures of LV stiffness, whereas other measures largely reflect LV relaxation.

Pulsed Doppler of pulmonary veins: Flow into the left atrium can be sampled. S, D, and A waves represent systolic and diastolic atrial filling. The A wave is generated by reverse flow into the pulmonary veins during atrial contraction.

• The S/D ratio increases with age, as LV diastolic relaxation declines. A pulmonary vein A wave duration more than 30 ms greater than transmitral A wave duration suggests elevated LV filling pressure.

CW Doppler of LV outflow/mitral inflow: Isovolumic relaxation time.

Tissue Doppler of medial and lateral mitral annuli (E’, A’)

• This is considered the least load-dependent filling variable. There is generally poor correlation between medial and lateral velocities, with the lateral annulus measurement being more reproducible.

• The E/E’ ratio correlates roughly with LV end-diastolic pressure; a ratio >15 is strongly suggestive of elevated filling pressure, and a ratio <8 strongly suggestive of normal filling pressure.

Colour Doppler flow propagation (CFP) slope: Rate of blood acceleration into the LV from the annulus to the apex.

Various diastolic profiles combining some of the above parameters have been suggested as indicators of degree or stage of ‘diastolic dysfunction’. (see Fig. 1.8). In general:

• markers of impaired relaxation (e.g. decreased E and E’ are accompanied by compensatory enhancement of A and A’), reduced pulmonary venous D, and reduced CFP slope.

• increases in LV filling pressure lead to pseudonormalization of the transmitral Doppler E/A ratio, with less effect on Doppler with Valsalva manoeuvre and tissue Doppler velocity ratios.

• as compliance decreases or a patient’s position on the LV pressure–volume curve advances (operating stiffness), the transmitral DT drops below 130 ms, early Doppler filling velocity is increased, and, due to elevated late diastolic LV pressures, atrial contraction and associated velocities are reduced.

• if E/E’ ratio <8 and LA is of normal size, symptoms are unlikely to be due to diastolic heart failure.

• do not miss constriction (see Constrictive pericarditis vs. restrictive myocardial disease, p. 475); look for:

• septal ‘bounce’ and dys-schrony.

• inferior vena cava (IVC) dilatation.

• hepatic vein expiratory reversal.