Page 52 - Medicine and Surgery

P1: JYS
BLUK007-02 BLUK007-Kendall May 25, 2005 17:25 Char Count= 0

48 Chapter 2: Cardiovascular system

regurgitation or refractory functional regurgitation may Sinus nodal arrhythmias
require operative repair (or rarely replacement).
Sinus bradycardia

Definition
Cardiac arrhythmias A sinus rate of less than 60 bpm.

A cardiac arrhythmia is a disturbance of the nor-
Aetiology
mal rhythm of the heart. Many arrhythmias are
It is a normal finding in athletes.
asymptomatic unless myocardial function is compro-
Sinusnode damage, e.g. myocardial infarction or de-
mised. Normal sinus rhythm is not exactly regular as
generation in old age.
there are fluctuations in autonomic tone with respi-
Hypothermia, hypothyroidism.
ration. On inspiration the parasympathetic tone falls
Drug therapy, e.g. β-blockers (including eye drops) or
and the heart rate increases, conversely on expiration
anti-arrhythmic drugs.
parasympathetic tone rises and the heart rate decreases.
Raised intra-cranial pressure due to increased vagal
This variation is normal and is referred to as sinus
discharge.
arrhythmia.
Severecholestaticjaundiceduetodepositionofbiliru-
Cardiac arrhythmias can be classified according to
bin in the conducting system.
whether they are bradycardias (<60 bpm) or tachycar-
dias (>100 bpm).
Bradycardiasmaybeduetodisordersofthesinusnode
Pathophysiology
or the atrioventricular (AV) node:
The cardiac output is a function of not only the heart
Sinusbradycardia and sinus node disease (also called

rate but also the stroke volume and hence in mild cases of
sick sinus syndrome).
sinus bradycardia there is no compromise of the cardiac
Atrioventricular block where the atria may be acting

output as a result of increased stroke volume.
normally, but the AV node does not conduct the im-
pulses normally to the ventricles.
Tachycardias are also subdivided according to their Clinical features
origin: Most patients are asymptomatic but occasionally post-
Sinustachycardia. MI or in the elderly, cardiac failure or hypotension may

Supraventricular tachycardia including atrial or junc- arise, as the stroke volume is unable to maintain cardiac

tional (AV nodal) tachycardias. output. If bradycardia is episodic and severe, syncope
Ventricular tachyarrhythmias such as ventricular may occur.

tachycardia and ventricular fibrillation are often sec-
ondary to ischaemic myocardial damage. Torsades de
pointes is a distinctive type of ventricular tachycardia Investigations
associated with a long Q–T interval with a character- Sinusbradycardia is diagnosed on ECG. Investigations
istic ECG (see page 55). ofcausesincludetemperature,thyroidfunctiontestsand
A useful clinical division is between narrow com- liver function tests if the patient is jaundiced.
plex tachycardias, which are due to supraventricular
(atrial or junctional) tachycardias, and broad complex
tachycardias, which are most often ventricular in ori- Management
gin. However, in patients with bundle branch block Most cases do not require treatment other than with-
and in cases where the rapid rate of supraventricu- drawal of drugs or treatment of any underlying cause.
lar tachycardias causes transient bundle branch block, In acute symptomatic sinus bradycardia intravenous at-
broad complex tachycardias can be supraventricular in ropine may be required. Chronic symptomatic brady-
origin. cardia may require a permanent cardiac pacemaker.