There are many causes of breathlessness (see Box 7.1). Everyone is breathless at times, but people who are physically unfit or who are overweight will be more breathless than others. Breathlessness can also result from anxiety, but when it is due to physical illness the important causes are anaemia, heart disease and lung disease; a combination of causes is common. Apart from ischaemia (see Ch. 6), cardiac diseases causing breathlessness include valve disease, cardiomyopathy and myocarditis. Box 7.2 summarizes the effects of these conditions on the heart, and the corresponding ECG features. The most important function of the history is to help to determine whether the patient does indeed have a physical illness and, if so, which system is affected. Breathlessness in heart disease is due to either increased lung stiffness, as a result of pulmonary congestion, or pulmonary oedema. Pulmonary congestion occurs when the left atrial pressure is high. A high left atrial pressure occurs either in mitral stenosis or in left ventricular failure. Pulmonary oedema occurs when the left atrial pressure exceeds the oncotic pressure exerted by the plasma proteins. Congestive cardiac failure (right heart failure secondary to left heart failure) can be difficult to distinguish from cor pulmonale (right heart failure due to lung disease). With both, the patient is breathless. Both are associated with pulmonary crackles in left heart failure due to pulmonary oedema, and in cor pulmonale due to the lung disease. Also in both, the patient may complain of orthopnoea. Both pulmonary congestion and lung disease can cause a diffuse wheeze. The diagnosis therefore depends on a positive identification, either in the history, examination or investigations, of heart or lung disease. The main value of the ECG in patients with breathlessness is to indicate whether heart disease of any sort is present, and to some extent whether the left or the right side of the heart is affected. The ECG is best at identifying rhythm abnormalities (which may lead to left ventricular impairment and so to breathlessness) and conditions affecting the left ventricle, particularly ischaemia. A patient with a completely normal ECG is unlikely to have left ventricular failure, although of course there are exceptions. Lung disease eventually affects the right side of the heart and may cause ECG changes, suggesting that significant lung disease is present. A sudden rhythm change is a common cause of breathlessness, and even of frank pulmonary oedema. Arrhythmias can be paroxysmal, so the patient may be in sinus rhythm when examined, and a patient who is suddenly breathless may not be aware of an arrhythmia. When sudden breathlessness is associated with palpitations it is important to establish whether the breathlessness or the palpitations came first; palpitations following breathlessness may be due to the sinus tachycardia of anxiety. The ECG in Fig. 7.1 is from a patient who developed pulmonary oedema due to the onset of uncontrolled atrial fibrillation. Less dramatic rhythm abnormalities can also contribute to breathlessness, especially to breathlessness on exertion. This is true of both fast and slow rhythms. The ECG in Fig. 7.2 is from a patient who had atrial fibrillation but who was breathless on exercise partly because of ventricular bigeminy (a coupled ventricular extrasystole following each normally conducted QRS complex), which markedly reduced cardiac output as a result of an effective halving of the heart rate. Left atrial hypertrophy causes a double (bifid) P wave. Left atrial hypertrophy without left ventricular hypertrophy is classically due to mitral stenosis, so the bifid P wave is sometimes called ‘P mitrale’. This is misleading, because most patients whose ECGs have bifid P waves either have left ventricular hypertrophy that is not obvious on the ECG or, and perhaps this is more common, have a perfectly normal heart (see Ch. 1, p. 14; Fig. 1.13). The bifid P wave is thus not a useful measure of left atrial hypertrophy. Fig. 7.3 shows an ECG with a bifid P wave indicating left atrial hypertrophy. This was confirmed by echocardiography in the patient, who also had concentric left ventricular hypertrophy due to hypertension. Significant mitral stenosis usually, but not always, leads to atrial fibrillation, in which no P waves, bifid or otherwise, can be seen. Occasional patients, such as the one whose ECG is shown in Fig. 7.4, develop pulmonary hypertension and remain in sinus rhythm. There is then a combination of a bifid P wave with evidence of right ventricular hypertrophy. This combination does suggest a diagnosis of severe mitral stenosis. Left ventricular hypertrophy may be caused by hypertension, aortic stenosis or incompetence, or mitral incompetence. The ECG features of left ventricular hypertrophy are: Left axis deviation is not uncommon, but is due more to fibrosis causing left anterior hemiblock than to the left ventricular hypertrophy itself. The complete ECG picture of left ventricular hypertrophy is easy to recognize. The ECG in Fig. 7.5 is from a patient with severe and untreated hypertension. It shows the ‘voltage criteria’ which, when combined with the T wave inversion in the lateral leads, probably are significant. In this case, the small Q waves in the lateral leads are septal and do not indicate a previous infarction. Note that the T wave inversion is most prominent in lead V6, and becomes progressively less so in leads V5 and V4. This pattern of T wave inversion is sometimes referred to as ‘left ventricular strain’, but this is an old-fashioned and essentially meaningless term. The most important cause of severe left ventricular hypertrophy is aortic valve disease: when aortic stenosis or incompetence causes left ventricular hypertrophy, aortic valve replacement must be considered. Aortic valve disease is frequently associated with left bundle branch block (LBBB) (Fig. 7.6), which completely masks any evidence of left ventricular hypertrophy. The patient who is breathless, or who has chest pain or dizziness, and has signs of aortic valve disease and an ECG showing LBBB, needs urgent investigation. However, it is important to remember the ECG cannot be used to assess severity or monitor progression of valvular heart disease. This will usually be assessed by echocardiography. Note
The ECG in patients with breathlessness
History and examination
Rhythm problems
The ECG in disorders affecting the left side of the heart
The ECG in left atrial hypertrophy
The ECG in left ventricular hypertrophy
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The ECG in patients with breathlessness
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Deep wide S wave in supraventricular beat in lead V6
Fig. 7.2
Bifid P wave in lead V3
Fig. 7.3
Bifid P wave in lead II
Fig. 7.4
Tall R wave and inverted T wave in lead V5
Fig. 7.5
Left bundle branch block with aortic stenosis