The Effects of Other Conditions on the ECG

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The Effects of Other Conditions on the ECG

The ECG is not a good method for investigating or diagnosing any condition that is not primarily cardiac. However, some generalized diseases do affect the ECG: it is important to recognize this, and not assume that a patient has heart disease simply because their ECG seems abnormal.

ARTEFACTS IN ECG RECORDINGS

THE EFFECTS OF ABNORMAL MUSCLE MOVEMENT

Although ECG recorders are designed to be especially sensitive to the electrical frequencies of cardiac muscle contraction, the ECG will also record the contraction of skeletal muscles. The most common pattern of ‘ECG abnormality’ is a high-frequency oscillation due to general muscular tension in a patient who is not properly relaxed.

Sustained involuntary tremors, such as those associated with Parkinsonism ( Fig. 7.1) cause rhythmic ECG abnormalities that may be confused with cardiac arrhythmias.

Fig. 7.1 Parkinsonism
Note

• Muscle tremor at 5/s gives an appearance resembling atrial flutter

• The irregular QRS complexes may indicate that the rhythm is actually atrial fibrillation

• This record demonstrates the importance of looking at the patient as well as the ECG

HYPOTHERMIA

Hypothermia causes shivering, and therefore artefacts due to muscular activity. However, there can be other changes in the ECG, and the characteristic ECG feature of hypothermia is the ‘]’ wave. This is a small hump seen at the end of the QRS complex ( Fig. 7.2).

Fig. 7.2 Atrial flutter, hypothermia
Note

• Atrial flutter with ventricular rate 26/min

• J waves visible in leads V₄–V₆

J wave in lead V₅

The ECG in Figure 7.2 was recorded from a 76-year-old woman who was admitted to hospital with a temperature of 30°C after lying for a prolonged period in a freezing house, after a fall. She initially had a heart rate of 26/min, and the rhythm was atrial flutter. J waves can be seen in the lateral chest leads. On re-warming, she began to shiver, and, despite the muscle artefact, her heart can be seen to have reverted to sinus rhythm with first degree block. J waves are still visible ( Fig. 7.3). When her temperature had returned to normal, the PR interval normalized and the J waves disappeared ( Fig. 7.4).

Fig. 7.3 Hypothermia
Note

• Same patient as in Figures 7.2 and 7.4

• Sinus rhythm is restored

• The patient has begun to shiver (muscle artefact in the limb leads, with a further artefact in the penultimate complex of the rhythm strip)

• First degree block

• J waves still visible

J wave in lead V₅

Fig. 7.4 Re-warming after hypothermia
Note

• Same patient as in Figures 7.2 and 7.3

• The patient is now in sinus rhythm with a normal PR interval

• J waves have disappeared

• There are some nonspecific ST segment and T wave changes in leads I–II, VL, V₆

No J wave in lead V₅

THE ECG IN CONGENITAL HEART DISEASE

The ECG provides a limited amount of help in the diagnosis of congenital heart disease by showing which chambers of the heart are enlarged. It is important to remember (see Ch. 1) that at birth the ECG of a normal infant shows a pattern of ‘right ventricular hypertrophy’, and this gradually disappears during the first 2 years of life.

If the infant pattern persists beyond the age of 2 years, right ventricular hypertrophy is indeed present. If there is a left ventricular, or normal adult, pattern before this age, then left ventricular hypertrophy is probably present. In older children the criteria for left and right ventricular hypertrophy are the same as in adults.

Box 7.1 lists some common congenital disorders and the associated ECG appearances.

The ECG in Figure 7.5 shows all the features of severe right ventricular hypertrophy: it came from a boy with severe pulmonary stenosis.

Fig. 7.5 Pulmonary stenosis
Note

• Sinus rhythm

• Right axis deviation

• Dominant R waves in lead V₁

• Persistent S waves in lead V₆

• Inverted T waves in leads V₁–V₄

Dominant R wave in lead V₁

The ECG in Figure 7.6 shows left ventricular hypertrophy, and was recorded in an 8-year-old with severe aortic stenosis.

Fig. 7.6 Left ventricular hypertrophy
Note

• Sinus rhythm

• Normal axis

• Left ventricular hypertrophy according to voltage criteria

• T wave inversion in leads I, V₅–V₆

Tall R wave and inverted T wave in lead V₆

The ECG in Figure 7.7 shows right ventricular hypertrophy, and came from a young woman who had had a partial correction of Fallot’s tetralogy 20 years previously.

Fig. 7.7 Right ventricular hypertrophy in Fallot’s tetralogy
Note

• Leads V₁–V₆ recorded at half sensitivity

• Sinus rhythm

• Right axis deviation

• Dominant R waves in lead V₁

• T wave inversion in leads II–III, VF, V₁–V₄

Dominant R wave in lead V₁

The ECG in Figure 7.8 suggests right atrial hypertrophy and shows right bundle branch block. It came from a teenager with Ebstein’s anomaly and an atrial septal defect.

Fig. 7.8 Right atrial hypertrophy and right bundle branch block, in Ebstein’s anomaly
Note

• Sinus rhythm

• Peaked P waves in lead II

• Broad QRS complexes with right bundle branch block pattern

Peaked P wave in lead II

It is usually fairly obvious that a patient has congenital heart disease of some sort, but the condition that may be missed is an atrial septal defect. The ECG in Figure 7.9 is from a 50-year-old woman who complained of mild but increasing breathlessness. She had a rather nonspecific systolic murmur at the left sternal edge. Her GP recorded an ECG which showed right bundle branch block, and as a result she had an echocardiogram which showed an atrial septal defect.