4.1 HEART FAILURE

There is no ideal definition of heart failure. One definition is of a clinical syndrome caused by an abnormality of the heart which leads to a characteristic pattern of haemodynamic, renal, neural and hormonal responses. A shorter definition is ventricular dysfunction with symptoms.

Echo plays a crucial role when heart failure is suspected (e.g. unexplained breathlessness, clinical signs such as raised venous pressure, basal crackles, third heart sound) to help establish the diagnosis, assess ventricular function and institute correct treatment.

An underlying cause of heart failure should always be sought and echo plays an essential role here also. The most common cause in Western populations is coronary artery disease. Echo may also reveal a surgically treatable underlying cause, e.g. valvular disease or LV aneurysm. Heart failure may be caused by severe AS (which affects 3% of those aged over 75 years) and the murmur at this stage may be absent.

Major therapeutic advances have been made in the past two decades, including the use of modern diuretics, angiotensin-converting enzyme (ACE) inhibitors, device therapy and cardiac transplantation. This has improved the quality and duration of life of many with heart failure.

Some studies (e.g. Framingham study) have provided epidemiological data on heart failure:

The term dilated cardiomyopathy describes large hearts with reduced contractile function in the presence of normal coronary arteries (section 4.4). It is usually of unknown cause. When a cause is established, the term is sometimes preceded by a qualifier, such as alcoholic dilated cardiomyopathy. Hypertension has become a less common cause of heart failure as a consequence of its improved detection and treatment. It remains an important contributory factor to the progression of heart failure and is a risk factor for coronary artery disease.

Causes of chronic heart failure

It is always important to seek the cause of worsening features (decompensation) of heart failure in a previously clinically stable individual. This may lead to symptoms such as breathlessness or signs such as crackles in the chest, raised venous pressure or peripheral oedema. Echo can help in the investigation of the potential causes:

There are many causes of acute heart failure, the most common of which is myocardial ischaemia or infarction.

4.2 ASSESSMENT OF LV SYSTOLIC FUNCTION

This is one of the most important and common uses of echo. LV systolic function is a major prognostic factor in cardiac disease and has important implications for treatment. Clinical management is altered if an abnormality is detected (e.g. the diagnosis of systolic heart failure should lead to the initiation of ACE inhibitors unless there is a contraindication).

LV systolic function can be assessed by M-mode, 2-D and Doppler techniques. M-mode gives excellent resolution and allows measurement of LV dimensions and wall thickness. 2-D techniques are often used to provide a visual assessment of LV systolic function, both regional and global. The general validity of this has been shown but there are inter-observer variations. Visual estimation is clinically useful but unreliable in those who have poor echo images, can be limited in value in serial evaluation and inadequate where LV volumes critically influence the timing of intervention. Computer software on the echo machine may be used to provide a quantitative assessment of LV function. Certain geometrical assumptions are made about LV shape which are not always valid, particularly in the diseased heart.

M-mode (Fig. 4.1) can be used to assess LV cavity dimensions, wall motion and thickness. The phrase, ‘a big heart is a bad heart’, carries an important element of truth – poor LV systolic function is usually associated with increased LV dimensions. This is not always the case, e.g. if there is a large akinetic segment of LV wall or an apical LV aneurysm following MI, systolic function may be impaired due to regional wall motion abnormalities but M-mode measurements of LV dimensions may be within the normal range.

Fig. 4.1 M-mode of left ventricle. This can be used to estimate cavity dimensions in systole and diastole, and wall thickness. It is important to identify the continuous endocardial echo and to distinguish this from echoes from chordae or mitral valve leaflet tips.

LV internal dimension measurements in end-systole (LVESD) and end-diastole (LVEDD) are made at the level of the MV leaflet tips in the parasternal long-axis view. Measurements are taken from the endocardium of the left surface of the interventricular septum (IVS) to the endocardium of the LV posterior wall (LVPW). The ultrasound beam should be as perpendicular as possible to the IVS. Care must be taken to distinguish between the endocardial surfaces and the chordae tendineae on the M-mode tracing.

LVEDD is at the end of diastole (R wave of ECG). The normal range is 3.5–5.6 cm.

LVESD is at the end of systole, which occurs at the peak downward motion of the IVS (which usually slightly precedes the peak upward motion of the LVPW) and coincides with the T wave on the ECG. The normal range is 2.0–4.0 cm.

Remember that the normal range for LVEDD and LVESD varies with a number of factors, including height, sex and age.

M-mode measurements can be converted to estimates of volume but this is inaccurate in regional LV dysfunction and spherical ventricles. The LVEDD and LVESD measurements can be used to calculate LV fractional shortening, LV ejection fraction and LV volume, which give some further indication of LV systolic function.

Fractional shortening (FS) is a commonly used measure and is the % change in LV internal dimensions (not volumes) between systole and diastole:

Normal range is 30–45%.

The LV volume is derived from the ‘cubed equation’ (i.e. volume, V = D³, where D is the ventricular dimension measured by M-mode). This assumes that the LV cavity is an ellipse shape, which is not always correct. There are some equations which attempt to improve the accuracy of this technique. The volume in end-diastole is estimated as (LVEDD)³ and in end-systole as (LVESD)³. The ejection fraction (EF) is the % change in LV volume between systole and diastole and is:

Normal range is 50–85%.

LV wall motion and changes in thickness during systole can be measured. The IVS moves towards the LVPW and the amplitude of this motion can be used as an indicator of LV function.

Wall thickness can also be measured. The walls thicken during systole. The normal range of thickness is 6–12 mm. Walls thinner than 6 mm may be stretched as in dilated cardiomyopathy or scarred and damaged by previous MI. Walls of thickness over 12 mm may indicate LV hypertrophy, an important independent prognostic factor in cardiovascular outcome risk.

2-D echo can be used qualitatively to assess LV systolic function by viewing the LV in a number of different planes and views. An experienced echo operator can often give a reasonably good visual assessment of LV systolic function as being normal, mildly, moderately or severely impaired, and whether abnormalities are global or regional.

2-D echo can also be used to estimate LV volumes and EF. Multiple algorithms may be used to estimate LV volumes from 2-D images but all make some geometrical assumptions which may be invalid. The area–length method (symmetrical ventricles) and the apical biplane summation of discs method (asymmetrical ventricles) are validated and normal values available.

A number of techniques are available. Simpson’s method (Fig. 4.2) divides the LV cavity into multiple slices of known thickness and diameter D (by taking multiple short-axis views at different levels along the LV long axis) and then calculating the volume of each slice (area × thickness). The area is π(D/2)². The thinner the slices, the more accurate the estimate of LV volume. Calculations can be made by the computer of most echo machines. The endocardial border must be traced accurately and this is often the major technical difficulty. Endocardial definition has improved with some newer echo technology (e.g. harmonic imaging) and automated endocardial border detection systems are available on some echo machines. The computer calculates LV volume by dividing the apical view into 20 sections along the LV long axis.

Fig. 4.2 Simpson’s method to estimate left ventricular volume.

The LV ejection fraction can be obtained from LV volumes in systole and diastole (as above). Alternatively, computer-derived data can be obtained by taking and tracing the LV endocardial borders of a systolic and a diastolic LV frame.

An estimate of cardiac output can be obtained using LV volumes:

Measurements of LV shape are an important and underutilized aspect of LV remodelling, e.g. after MI. Increasing LV sphericity has prognostic importance and loss of the normal LV shape may be an early indicator of LV dysfunction. 2-D echo allows a simple assessment of LV shape (measuring the ratio of long axis length to mid-cavity diameter).

The location and extent of wall motion abnormality following MI correlates with LV EF and is prognostically useful.

4.3 CORONARY ARTERY DISEASE

Echo plays an increasingly important role in assessing coronary artery disease. Resting and stress echo (Ch. 5) techniques are used in:

Assessment of ischaemia

Ischaemia results in immediate changes which can be detected by echo:

• Abnormalities of wall motion (hypokinetic, akinetic, dyskinetic)^*

• Abnormalities of wall thickening (reduced or absent systolic thickening or systolic thinning – this is more sensitive and specific for ischaemia)^*

• Abnormalities of overall LV function (e.g. ejection fraction).

These can be detected by 2-D echo but M-mode is also extremely good because its high sampling rate makes it very sensitive to wall motion and thickening abnormalities. It is essential that the beam is at 90º to the wall. There are limited regions of the LV myocardium that can be examined by M-mode – most usefully, the posterior wall and IVS (Fig. 4.3).

Fig. 4.3 (a) and (b) Dilated left ventricle with impaired systolic function due to coronary artery disease.

The changes reverse if ischaemia is reversed, e.g. by rest, anti-anginal medication, percutaneous transluminal coronary angioplasty, thrombolysis or coronary artery bypass grafting. If the myocardium has its blood supply occluded for more than 1 h, permanent changes occur which include MI and scarring.

Complications of myocardial infarction

Many of the complications of acute MI can be detected by echo.

• Acute heart failure due to extensive MI. This leads to pump failure which may result in cardiogenic shock. Echo shows severe LV impairment.

In the following 2 complications (acute MR and acute VSD), LV systolic function is very active, unlike the situation above.

• Acute MR. This may be due to papillary muscle dysfunction or rupture (Fig. 4.4) or chordal rupture, which may be shown by 2-D echo. There may be a flail MV leaflet. The MR jet can be seen on continuous wave or colour flow mapping.

• Acute VSD. This is often near the cardiac apex and is more common in inferior and RV infarction. A discontinuity in the IVS can be seen on 2-D echo in the apical 4-chamber, parasternal long-axis and short-axis views. Colour flow mapping can show the defect. Pulsed wave Doppler moved along the RV side of the IVS (parasternal long-axis or sometimes 4-chamber views) can show the jet.

• Mural thrombus (Fig. 4.5). This is shown on 2-D echo. It is usually located near an infarcted segment or aneurysm.

• LV aneurysm. Most frequently seen at or near the apex. More common in anterior than inferior MI. Best seen on 2-D echo. These can vary in size from small to very large, sometimes larger than the LV.

• Pseudoaneurysm (false aneurysm). This is rare. It follows rupture of the LV free wall and leads to haemopericardium (blood in the pericardial space), tamponade and is usually rapidly fatal. Sometimes, the haemopericardium clots and seals off the hole in the LV and a false aneurysm forms. 2-D echo is a good way to diagnose this. It is important to detect, as it needs urgent surgical resection before it ruptures. It can be difficult to distinguish it from a true aneurysm but the communicating neck is usually narrower than the diameter of the aneurysm, the walls are thinner and its size changes in the cardiac cycle (expands in systole) and it is more often filled with thrombus.

• Pericardial effusion complicating MI can be detected by M-mode or 2-D echo.

• Myocardial function after MI. This gives an indication of prognosis. The scarred myocardium is seen as a thin segment which does not thicken during systole and has abnormal motion. Echo can assess the extent of MI, evaluate LV systolic and diastolic function and look at residual complications.

Fig. 4.4 (a) and (b) Papillary muscle rupture following acute myocardial infarction. The muscle (arrows) and the posterior mitral valve leaflet can be seen to prolapse into the left atrium. TOE study.

Fig. 4.5 Thrombus in the apex of the left ventricle (arrows) following myocardial infarction. (a) Apical 4-chamber view and (b) apical 2-chamber view showing 2 distinct masses.

Echo assessment of coronary artery anatomy (Fig. 4.6)

Echo is not yet able to give a very accurate assessment of most parts of the coronary anatomy. The origins of the left and right coronary arteries may be seen in some transthoracic echo studies by using a modified parasternal short-axis view at AV level.

Fig. 4.6 Huge dilatation of the right coronary artery (RCA, arrow) due to coronary fistula. TOE short-axis study at aortic valve level.

Abnormalities are more likely to be seen during TOE, e.g.

• Anomalous origin of coronaries (e.g. origin from PA)

• Coronary artery fistula

• Aneurysm, e.g. Kawasaki syndrome, an acquired condition in children with coronary aneurysms which may be several centimetres in diameter.

4.4 CARDIOMYOPATHIES AND MYOCARDITIS

The cardiomyopathies are a diverse group of disorders. Cardiomyopathy means heart muscle abnormality, and strictly speaking the term should be applied to conditions that have no known underlying cause. These are known as idiopathic cardiomyopathies. The term has been extended to include conditions where there is an underlying cause (e.g. alcoholic, ischaemic, hypertensive cardiomyopathy etc.)

The most important idiopathic cardiomyopathies are:

1. Hypertrophic cardiomyopathy

This is an autosomal dominant condition with a high mutation rate (up to 50% of cases are sporadic). It is rare with an incidence of 0.4 –2.5 per 100 000 per year. A number of mutations of cardiac proteins have been identified as underlying causes. These include β-myosin heavy chain, myosin-binding protein C, α-tropomyosin and troponin T.

The clinical features include:

• Angina with normal coronary arteries – due to ventricular hypertrophy and myocardial oxygen supply/demand imbalance)

• Arrhythmias

• Breathlessness

• Syncope

• Sudden cardiac death (annual death rate is 3% in adults) – due to outflow tract obstruction or arrhythmia

• Ejection systolic murmur which may be confused with valvular aortic stenosis

• Heart failure (10–15%).

The characteristic feature is myocardial hypertrophy in any part of the ventricular wall:

• IVS to a greater extent than the free wall (termed asymmetrical septal hypertrophy or ASH) – 60% of cases

• Concentric – 30% of cases

• Apical – 10% of cases

• RV hypertrophy – 30% of cases and correlates with severity of LVH.

Hypertrophy, particularly of the septum, may cause LV outflow tract obstruction (LVOTO). In this situation, the term hypertrophic obstructive cardiomyopathy (HOCM) is appropriate. This ‘dynamic’ obstruction becomes more pronounced in the later stages of systole. As the LV empties, LV cavity size becomes smaller and the anterior MV leaflet moves anteriorly to contact the septum. It may be present at rest or become more pronounced with exercise. In some individuals with HCM, the most dangerous time is at the end of vigorous exercise, e.g. at half-time in a football match. At this time, ventricular volumes diminish as cardiac output and heart rate decrease, catecholamine drive decreases and there may be changes in circulating electrolyte concentrations, such as K⁺. These features all combine to increase the risk of syncope and sudden death by increasing the likelihood of LVOTO and arrhythmias.

Echo is diagnostic of HCM. The important echo features are seen using both M-mode and 2-D imaging:

1. Asymmetrical septal hypertrophy (ASH) (Fig. 4.7)

2. Systolic anterior motion (SAM) of the MV apparatus which may abut the IVS. This may not be seen at rest but may occur following provocation by the Valsalva manoeuvre or isovolumic exercise

3. Midsystolic AV closure and fluttering.

Fig. 4.7 Hypertrophic cardiomyopathy. (a) Asymmetrical septal hypertrophy (arrow). (b) Fluttering and premature mid-systolic closure of the aortic valve (arrow). (c) Continuous Doppler showing a peak velocity across the left ventricular outflow tract of 5.6 m/s (estimated peak gradient 127 mmHg).

The definition of asymmetrical hypertrophy varies but a septal to posterior wall ratio of 1.5 or more is unequivocal evidence of asymmetry.

Neither ASH nor SAM is specific for HCM. ASH may occur in AS and SAM may occur in MV prolapse. Their occurrence together is strongly suggestive of HCM.

Continuous wave Doppler shows increased peak flow through the LVOT. Pulsed wave Doppler with the sample volume in the LVOT proximal to the AV shows that the increase in velocity occurs below the level of the valve, distinguishing the obstruction from valvular aortic stenosis. The peak in maximal velocity across the AV is often bifid in HCM. There may also be features of LV diastolic dysfunction due to LVH (e.g. abnormal transmitral flow pattern with E-wave smaller than A-wave, section 4.5).

2. Dilated cardiomyopathy

This is characterized by dilatation of the cardiac chambers, particularly the LV (although all other chambers are often involved) with reduced wall thickness and reduced wall motion (Fig. 4.8). The incidence is estimated at 6.0 per 100 000 per year. Most cases are isolated although some familial forms have been identified. The reduced LV wall motion is usually global rather than regional, as seen in LV systolic impairment due to coronary artery disease (ischaemia or infarction).

Fig. 4.8 (a) and (b) Dilated left ventricle with impaired systolic function due to dilated cardiomyopathy. Parasternal long-axis view and M-mode.

M-mode and 2-D echo show:

• Dilatation of all the cardiac chambers (left and right ventricles and atria) – increased LVESD and LVEDD

• Reduced wall thickness and motion (ranging from mild to severe impairment) – reduced ejection fraction and fractional shortening, reduced motion of IVS and LVPW

• Intracardiac thrombus (LV and LA).

Doppler studies may show functional MR and TR.

A number of conditions give rise to a clinical picture which is similar to idiopathic dilated cardiomyopathy. These include toxins such as alcohol and certain drugs, especially those used in the treatment of some cancers.

Chemotherapy with doxorubicin produces a dose-dependent degenerative cardiomyopathy. Cumulative doses should be kept to below 450–500 mg/m². Subtle abnormalities of LV systolic function (increased wall stress) are found in approximately 1 in 6 patients receiving only one dose of doxorubicin. Most patients who receive at least 228 mg/m² show either reduced contractility or increased wall stress. Baseline and re-evaluation echo should be carried out in individuals receiving doxorubicin. Further administration appears to be safe if resting EF remains normal, and dangerous if EF is low. Early abnormalities of diastolic function (in the absence of systolic abnormalities) may occur in patients receiving 200–300 mg/m².

3. Restrictive cardiomyopathy

This is characterized by increased myocardial stiffness or impaired relaxation and abnormal diastolic function of one or both ventricles. A number of disorders give rise to a clinical picture of restrictive cardiomyopathy:

1. Idiopathic

2. Infiltrations – amyloid, sarcoid, haemochromatosis, glycogen storage diseases (e.g. Pompe’s), mucopolysaccharidoses (e.g. Gaucher’s, Fabry’s)

3. Endomyocardial fibrosis – hypereosinophilic syndrome (Loeffler’s endomyocardial fibrosis), carcinoid, malignancy.

The echo assessment is difficult and the features are not specific. If features of restrictive cardiomyopathy are present, evidence of myocardial infiltration or endomyocardial fibrosis should be sought. The echo differentiation between restrictive cardiomyopathy and constrictive pericarditis can be difficult but is important as it has management implications.

Echo features of restrictive cardiomyopathy

• LV and RV cavity sizes are usually normal or only mildly increased, but there is impaired contractility of the ventricular walls seen on M-mode and 2-D echo. There may be dilatation of the LA and RA.

• Impaired LV and RV diastolic function. This is best assessed by Doppler echo. There is often a characteristic abnormal ‘restrictive pattern’ of MV flow with a very large E-wave and small A-wave (section 4.5).

Infiltration

The findings are similar whatever the underlying cause. Amyloid is the most common infiltrative disease (Fig. 4.9). The features are:

• Concentric thickening of the LV and RV free walls and septum and the interatrial septum

• LV and RV internal dimensions are often reduced

• Reduced wall and septal motion

• Failure of systolic thickening of the IVS and LV free wall

• Patches of high intensity ‘speckling’ in the hypertrophied muscle

• Thickening of the MV and TV leaflets with regurgitation (aortic and pulmonary valves may also be thickened)

• Pericardial effusion

• LV diastolic impairment with or without systolic impairment

• Intracardiac thrombus.

Fig. 4.9 Amyloid heart disease. (a) There is left ventricular and right ventricular hypertrophy, with apical obliteration of the right ventricle cavity with thrombus (arrow). The atria are dilated and the interatrial septum is thickened (arrow), as are the valve leaflets. (b) Hypertrophy and speckling of the interventricular septum (arrow).

Endomyocardial fibrosis

• Cavity obliteration especially at the RV and LV apex due to fibrosis or eosinophilic infiltration

• Bright echogenic endocardium

• Normal or thickened LV walls with reduced contractility

• Normal LV or reduced cavity size

• Similar changes in RV to LV

• Dilated RA and LA

• Intracardiac thrombus

• LV diastolic impairment with or without systolic impairment.

4.5 DIASTOLIC FUNCTION

Clinical features of left heart failure may occur in individuals with normal or near-normal LV systolic function assessed by echo, due to diastolic dysfunction, systolic impairment on exertion or ischaemia.

Diastolic function of the LV relates to chamber stiffness and relaxation following ventricular contraction. It is not a passive phenomenon and requires energy. Abnormalities of LV diastolic function occur in a number of conditions and can be assessed by echo but their assessment is rather complex. These abnormalities may co-exist with abnormalities of systolic function, or may occur in isolation or before systolic impairment becomes obvious.

Diastole has 4 periods – isovolumic relaxation, early rapid filling, late filling and atrial systole. Abnormalities in any of these may contribute to diastolic heart failure.

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