Sinus nodal arrhythmias
A sinus rate of less than 60 bpm.
It is a normal finding in athletes.
Sinus node damage, e.g. myocardial infarction or degeneration in old age.
Drug therapy, e.g. ő≤-blockers (including eye drops) or anti-arrhythmic drugs.
Raised intra-cranial pressure due to increased vagal discharge.
Severe cholestatic jaundice due to deposition of bilirubin in the conducting system.
The cardiac output is a function of not only the heart rate but also the stroke volume and hence in mild cases of sinus bradycardia there is no compromise of the cardiac output as a result of increased stroke volume.
Most patients are asymptomatic but occasionally post-MI or in the elderly, cardiac failure or hypotension may arise, as the stroke volume is unable to maintain cardiac output. If bradycardia is episodic and severe, syncope may occur.
Sinus bradycardia is diagnosed on ECG. Investigations of causes include temperature, thyroid function tests and liver function tests if the patient is jaundiced.
Most cases do not require treatment other than withdrawal of drugs or treatment of any underlying cause. In acute symptomatic sinus bradycardia intravenous atropine may be required. Chronic symptomatic bradycardia may require a permanent cardiac pacemaker.