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Chapter 2: Cardiac arrhythmias 49

Sinus tachycardia rate may be regular, bradycardic, tachycardic or variable
with pauses. Carotid sinus massage typically leads to a
Definition
sudden and sometimes prolonged sinus pause. It should
Sinus rate above 100 bpm.
therefore only be attempted where there is monitoring
and resuscitation equipment.
Aetiology/pathophysiology
Sinustachycardia is a physiological response to main-
tain tissue perfusion and oxygenation. Causes include Complications
exercise, fever, anaemia, hypovolaemia, hypoxia, heart The most important complication is cardiac syncope, as
failure, hyperthyroidism, pulmonary embolism, drugs in other forms of bradycardia. It may develop associated
and emotion. AVnodalblockandIncreasedriskofthromboembolism.

Clinical features
Investigations
Palpitations with an associated rapid, regular pulse rate.
The diagnosis is usually made with a 24-hour ECG.
Features of any underlying cause often predominate.
Twelve-lead ECG may show evidence of underlying is-
chaemia or previous myocardial infarction.
Investigations
The ECG confirms sinus rhythm and demonstrates the
tachycardia. Appropriate investigations of the underly- Management
ing cause may be required. Permanent pacing is required for symptomatic patients.
In addition anti-arrhythmic drugs may be required to
controlanytachycardia.Patientsrequireanticoagulation
Management
to reduce the risk of thromboembolism.
Treatment is aimed at the underlying cause. β-blockers
can slow the rate, but this is rarely of clinical benefit.
Atrial arrhythmias
Sinus node disease
Atrial ectopic beats
Definition
Sinusnode disease or sick sinus syndrome is a tachy- Definition
cardia/bradycardia resulting from damage to the sinus Atrial ectopic beats include extrasystoles and premature
node. beats.

Aetiology/pathophysiology Aetiology
Sinusnode disease is relatively common in the elderly Atrial ectopics are common in normal individuals. All
dueto ischaemia, infarction or degeneration of the sinus cardiac cells have intrinsic pacemaker ability. They grad-
node. The condition is characterised by prolonged in- ually depolarise until a threshold is reached at which
tervals between consecutive P waves (sinus arrest) and point rapid depolarisation occurs and a cardiac action
periods of sinus bradycardia. Pauses in the sinus rhythm potential is fired. This is most rapid in the sinoatrial
may allow tachycardias (typically atrial fibrillation) from node, the normal pacemaker of the heart. If in a single
other foci to emerge. This combination of fast and slow or group of cells the gradual depolarisation is more rapid
supraventricular rhythms is known as tachy-brady syn- than usual, or if the voltage threshold for rapid depolar-
drome. isation is reduced they may stimulate a cardiac depolari-
sation resulting in an ectopic beat. This process is termed
Clinical features enhanced automaticity. Common causes are electrolyte
Tachycardiamaycausepalpitations,andlongpausesmay abnormalities, alcohol or nicotine excess, anaemia, med-
cause dizziness and syncope. On examination the pulse ications such as β-agonists, and hypoxaemia.