Clinical case 1 - Dizziness in 78 year old man

A 78-year-old man is brought to hospital with an episode of dizziness. He was well until the last 6 months, since when he has had some falls, irregularly. On some occasions he lost consciousness and is unsure how long he has been unconscious. On a few occasions he has fallen, grazing his knees and on others he has felt dizzy and has had to sit down but has not lost consciousness. These episodes usually happened on exertion, but once or twice they have occurred while sitting down. He recovers over 10–15 min after each episode.

Once, his wife was with him when he blacked out. Worried, she called an ambulance. He looked so pale and still that she thought that he had died. He was taken to hospital, by which time he had recovered completely and was discharged and told that he had a normal electrocardiogram (ECG) and chest X-ray.

On examination

He is pale with a blood pressure of 93/63 mm Hg.

The pulse rate is 35/min, regular.

There are no heart murmurs.

The jugular venous pressure is raised 3 cm with occasional rises.

There is no leg edema and all the peripheral pulses are palpable.

An ECG was performed and is shown below.

1) What does the ECG show?

2) Why does the history tell us about the disease?

Discussion:

1) The ECG is a classic case of third degree AV block aka complete heart block. For more on the ECG please read third-degree-atrioventricular-block , one of my earlier articles on how to diagnose complete heart block on ECG.

2) The blackouts do not seem to have had any relationship to posture. The one witnessed episode seems to have been associated with loss of colour. This suggests a loss of cardiac output usually associated with an arrhythmia. This may be the case despite the absence of any other cardiac symptoms.

The episodes of loss of consciousness are called Stokes–Adams attacks and are caused by self-limited rapid tachyarrhythmias at the onset of heart block or transient asystole. Although these have been intermittent in the past he is now in stable complete heart block and, if this continues, the slow ventricular rate will be associated with reduced cardiac output which may cause fatigue, dizziness on exertion or heart failure. Intermittent failure of the escape rhythm may cause syncope.

On examination, the occasional rises in the jugular venous pressure are intermittent ‘cannon’ a-waves as the right atrium contracts against a closed tricuspid valve.

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