recognition of atrial fibrillation

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E C G E D U C AT I O N
RECOGNITION OF ATRIAL
FIBRILLATION
Part five of an educational series on ECG analysis and arrhythmia diagnosis
Dr I W P Obel — Specialist Cardiologist
Milpark Hospital, Johannesburg
Atrial fibrillation (AF) is the commonest and probably the least satisfactorily treated sustained arrhythmia
that we all have to deal with. It is common alone and
together with other diseases (cardiac and general).
There is a close association between AF and heart failure, both as a consequence and as a cause. The development of AF together with decompensation in heart
failure cases is well known, regardless of the cause of
the heart failure. AF may occur in otherwise normal people and the incidence increases with age, reaching up
to 15% or more in the aged. The consequences of AF
include a decreased life expectancy, either together with
or separate from other forms of heart disease, a high
incidence of morbidity and a clear decrease in quality
of life.
PATHOPHYSIOLOGY
In the atrium there is complete loss of organised contraction, which is probably due to re-entering of small circuits. AF is frequently induced by atrial ectopic beats
arising either in the right or left atrium, or from within
the pulmonary veins. Persistence of AF requires a suitable substrate. This is initially chemical and electrical
but is soon associated with an increase in left atrial
size, even in the absence of other cardiac disease. The
chaotic atrial contractions are associated with a wavy
line on the ECG and an absence of visible P waves. The
ECG is entirely different from one with atrial flutter
where organised (although rapid) atrial contractions are
seen.
Conduction to the ventricles
Since the AV node is bombarded by many hundreds of
impulses per minute, conduction varies; often dependent
on the functional status of the AV node. (Conduction will
be facilitated by sympathetic influences and cate-
cholamines and diminished by parasympathetic influences and some drugs.) The ventricular response, therefore, is always irregular independent of the presence of
bundle branch block or an accessory pathway (WolffParkinson-White syndrome).
Pathophysiological consequences depend on the
loss of atrial contraction and the often rapid (but irregular) ventricular rate. Thrombosis mainly in the left atrium
with the danger of embolism, commonly with stroke, is
very frequent. There may be a decrease in cardiac output, particularly on exercise, and a rise in diastolic ventricular pressure. Consequently heart failure is aggravated, unmasked or even caused.
THE ELECTROCARDIOGRAM
No organised atrial contraction (P wave) can be seen.
The atrial tracing varies from extremely fine (nothing
may be seen to represent atrial contraction) to fairly
coarse. The QRS complexes occur irregularly
and are often very rapid.
The QRS configuration varies from being completely normal (narrow) to broad if there is bundle branch block
present (or when there is an accessory pathway).
Sometimes the QRS may be broader in some beats than
in others due to varying functional bundle branch block
or competing conduction via the AV node and an accessory pathway.
Other electrocardiographical features are those of any
underlying condition that may be present. For example,
left ventricular hypertrophy, previous infarction, a rightward QRS axis and right ventricular enlargement in the
presence of mitral stenosis, etc.
When to refer
In view of the very important consequences of AF and
the therapeutic choices currently available, all patients
with AF should, in my opinion, be referred for specialist
June 2004 Vol.22 No.6 CME
337
E C G E D U C AT I O N
Fig.1. ECG with intracardiac recordings. RA is recorded from the right atrium. Note the extremely rapid, irregular, disorganised waves varying in size. Compare this with the well-formed ventricular waves (RV). STD II and VI
show the irregular ventricular contractions. The 2 broad beats at the end show right bundle branch block.
cardiological assessment. This is urgent if the QRS complex is broad (>120 ms – 3 small squares) since bundle
branch block or Wolff-Parkinson-White syndrome may
be present. Should the patient’s course change, either
owing to worsening heart failure or uncontrollable AF,
re-referral is strongly recommended.
DIFFERENTIAL DIAGNOSIS IN A NUTSHELL
An irregular ECG without a P wave before each QRS can
be found in a number of conditions. This would include
2nd-degree heart block, atrial or ventricular ectopic beats,
atrial flutter and some ventricular arrhythmias such as polymorphous ventricular tachycardia.
Atrial and ventricular ectopy can be distinguished by the
regular effect the extra beat has on the rhythm, principally
the next beat. With atrial ectopy an abnormal P wave
may precede the extra beat.
Atrial flutter can usually be differentiated based on the fact
that most R-R intervals are regular, although the degree of
338 CME June 2004 Vol.22 No.6
block may vary, e.g. from 2:1 to 4:1, etc. A definite pattern to the irregularity is present.
Polymorphous ventricular tachycardia is differentiated, usually by the fact that all QRS complexes are broad and
configuration varies from beat to beat. They have a specific pattern (e.g. Torsades de Pointes, which will be discussed in a later article in the series). Polymorphous ventricular tachycardia invariably occurs in the setting of an
acutely ill patient, e.g. myocardial infarction and syncopal
episodes.
E C G E D U C AT I O N
Fig.2. Atrial fibrillation – although the rhythm appears regular (and very fast)
measurement proves it to be irregular as in Fig.3.
Fig.3. Typical atrial fibrillation with irregularity of QRS complexes. Compare
Fig.2.
A SPECIAL INTEREST GROUP OF SA HEART ASSOCIATION
P.O. Box 2826, Benoni, 1500
E-mail: [email protected]
Fax: 021-448 7062
This article is sponsored by Johnson & Johnson Medical,
in the interest of continued medical education
For more information and referrals, please send your request to [email protected]
June 2004 Vol.22 No.6 CME 339
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