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50 Chapter 2: Cardiovascular system

Pathophysiology ofarecurrentcycleofdepolarisationorcircusmovement
As the depolarisation of the heart arises from within the (also termed re-entry).
atria, the QRS complex of the ECG is preceded by a P In atrial flutter the circuit is single and has a character-
wavewhichmaybeofdifferentconfigurationasatrialde- isticlocationintherightatriuminvolvinganareacloseto
polarisation has a different origin to normal. The QRS the entrance of the vena cavae. This relatively fixed phys-
complex is the same as normal because the depolarisa- ical characteristic explains the typical ECG appearance
tion of the ventricles begins from the AV node. and consistent cycle length between individual patients.
Whilst the atrial rate is between 280 and 350 beats, the
Clinical features normal atrioventricular delay in the AV node limits the
Patients are often asymptomatic but may complain of ventricular rate. This usually produces a 2:1, 3:1 or 4:1
an irregular or thumping heartbeat. The patient may atrioventricular block.
complain of a skipped beat, as there is a compensatory
pause after an extrasystole.
Clinical features
Atrial flutter presents with palpitations, dizziness, syn-
Investigations cope or cardiac failure. It may occur persistently or in
ECG shows early, abnormal P waves followed by a nor- episodes (paroxysmal atrial flutter) that last minutes or
mal QRS complex and a compensatory pause. Ectopic P hours to days. The pulse rate is dependent on the de-
waves are often best seen in lead V1. gree to which the AV node blocks the rate but is most
commonly around 150 bpm (2:1 block). Massage of the
Management carotid sinus causes a transient increase in block with
Atrial ectopic beats do not require treatment, although consequent slowing of the ventricular rate.
underlying causes of increased automaticity should be
identified and managed. If atrial ectopic beats are fre-
Investigations
quent they may progress to other atrial arrhythmias.
Atrial flutter produces a characteristic regular sawtooth
‘flutter’ waves at a rate of 300 bpm seen best in lead V1.
Atrial flutter If there is 2:1 block, the QRS complexes often obscure
the flutter waves, but carotid sinus massage should reveal
Definition
them (see Fig. 2.6).
Atrial flutter is a rapid atrial rate between 280 and 350
bpm, most commonly 300 bpm.
Management
DC cardioversion is the best treatment to restore si-
Aetiology
nusrhythm rapidly. Drug treatment is used to control
Atrial flutter is almost always a complication of my-
the ventricular rate, prevent recurrence and may occa-
ocardial disease such as ischaemic, hypertensive and
sionally restore sinus rhythm. Following electrophysio-
rheumatic heart disease, cardiomyopathies, myocarditis
logical assessment, recurrence may be prevented by ra-
and constrictive pericarditis. It may be caused by thyro-
diofrequency ablation of atrial flutter circuits. Digoxin
toxicosis.
increases AV block and reduces the ventricular rate,
amiodorone may restore sinus rhythm and reduce the
Pathophysiology
frequency of paroxysms.
Normally once a cardiac cell has been depolarised it is
refractory to re-stimulation for a short period. This pre-
vents waves of cardiac depolarisation flowing in a retro- Atrial fibrillation
grade direction. If, however, the conduction through the
myocardiumisslow(usuallyduetomyocardialdamage), Definition
adjacent cells may have recovered from their refractory Atrial fibrillation is a quivering of atrial myocardium
period allowing restimulation and hence the formation resulting from disordered electrical and muscle activity.