The ECG in Patients with Breathlessness

6


The ECG in Patients with Breathlessness




HISTORY AND EXAMINATION


There are many causes of breathlessness (see Box 6.1). 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. 5), cardiac diseases causing breathlessness include valve disease, cardiomyopathy, and myocarditis including acute rheumatic fever. Boxes 6.2–6.6 summarize 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.



Box 6.1   Underlying causes of breathlessness


Physiological and psychological



Heart disease left ventricular failure



Heart disease high left atrial pressure



Lung disease



Pericardial disease



Anaemia



Box 6.4   The ECG in hypertrophic cardiomyopathy





Box 6.2   The ECG in valve disease


Mitral stenosis



Mitral regurgitation



Aortic stenosis



Aortic regurgitation



Mitral valve prolapse



Note: abnormalities can vary in different records from the same individual


Biventricular hypertrophy




Box 6.3   The ECG in congestive cardiomyopathy





Box 6.5   The ECG in myocarditis





Box 6.6   The ECG in acute rheumatic fever




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. In heart failure, this is due to the return to the effective circulation of blood that was pooled in the legs. In patients with chest disease (especially chronic obstructive airways disease), orthopnoea results from the need to use diaphragmatic respiration. Both pulmonary congestion and lung disease can cause a diffuse wheeze. The diagnosis therefore depends on a positive identification, either in the history or on examination, 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 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. The patient with a completely normal ECG is unlikely to have left ventricular failure, though 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.



RHYTHM PROBLEMS


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 Figure 6.1 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 Figure 6.2 is from a patient who had atrial fibrillation but who was breathless on exercise partly because of coupled ventricular extrasystoles, which markedly reduced cardiac output as a result of an effective halving of the heart rate.




THE ECG IN DISORDERS AFFECTING THE LEFT SIDE OF THE HEART



THE ECG IN LEFT ATRIAL HYPERTROPHY


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. The bifid P wave is thus not a useful measure of left atrial hypertrophy.


Figure 6.3 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 Figure 6.4, 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 allow a confident diagnosis of severe mitral stenosis.




THE ECG IN LEFT VENTRICULAR HYPERTROPHY


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 ECG is a poor guide to the severity of left ventricular hypertrophy. Numerous criteria have been proposed that claim to detect the presence of left ventricular hypertrophy from ECG measurements. Most depend on measuring R or S waves in different leads, and some take the width of QRS complexes into account. The most commonly used indicators are the Sokolow-Lyon voltage criteria. These define left ventricular hypertrophy as being present when the depth of the S wave in lead V1 plus the height of the R wave in lead V5 or V6 (whichever is the greater) exceeds 35 mm, although the S wave is usually also deep in lead V2.


Unfortunately, voltage criteria have a low sensitivity as detectors of left ventricular hypertrophy, and are essentially useless. They would frequently lead to a diagnosis of left ventricular hypertrophy in perfectly healthy young men, even in those who are not athletic ( Fig. 6.5).

Related posts:

  1. Conclusions: Four Steps to Making The Most of the ECG
  2. The ECG When the Patient has a Tachycardia
  3. The ECG in Healthy People
  4. The ECG in Patients with Chest Pain

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Jul 26, 2016 | Posted by in CARDIOLOGY | Comments Off on The ECG in Patients with Breathlessness

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