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.
Comments
Post a Comment