atrial rhythms

Question 1

ectopic atrial tachycardia

AKA paroxysmal atrial tachycardia (PAT), unifocal atrial tachycardia

Answer 1

rate: 100-180
rhythm: regular
p wave: present, may be different w/ ectopy
P:QRS ratio: 1 to 1
PR interval- normal, different w/ ectopy
qrs widtch: <120 ms (0.12 seC)

Atrial rate > 100 bpm.
P wave morphology is abnormal when compared with sinus P wave due to ectopic origin.
There is usually an abnormal P-wave axis (e.g. inverted in the inferior leads II, III and aVF)
At least three consecutive identical ectopic p waves.
QRS complexes usually normal morphology unless pre-existing bundle branch block, accessory pathway, or rate related aberrant conduction.
Isoelectric baseline (unlike atrial flutter).
AV block may be present — this is generally a physiological response to the rapid atrial rate, except in the case of digoxin toxicity where there is actually AV node suppression due to the vagotonic effects of digoxin, resulting in a slow ventricular rate (“PAT with block”).

Question 2

wandering atrial pacemaker

Answer 2

rate: < 100bpm
rhythm: irregulary-irregular
p wave: at least 3 different morphologies
P:QRS ratio: 1 to 1
PR interval- variable
qrs widtch: <120 ms (0.12 seC)

*T wave normal. If heart rate exceeds 100 bpm, then rhythm may be multifocal atrial tachycardia (MAP)

Question 3

multifocal atrial tachycardia

Answer 3

rate: > 100bpm
rhythm: irregulary-irregular
p wave: at least 3 different morphologies
P:QRS ratio: 1 to 1
PR interval- variable
qrs widtch: <120 ms (0.12 seC)

Question 4

atrial flutter

Answer 4

rate: atria (250-350), ventricles (125-175)
rhythm: usually regular
p wave: saw toothed “f waves”
P:QRS ratio: variable, 2:1 is common
PR interval- variable
qrs widtch: <120 ms (0.12 seC)

Atrial flutter is a type of supraventricular tachycardia caused by a re-entry circuit within the right atrium.

The length of the re-entry circuit corresponds to the size of the right atrium, resulting in a fairly predictable atrial rate of around 300 bpm (range 200-400).

Ventricular rate is determined by the AV conduction ratio (“degree of AV block”).
The commonest AV ratio is 2:1, resulting in a ventricular rate of ~150 bpm.

Higher-degree AV blocks can occur — usually due to medications or underlying heart disease — resulting in lower rates of ventricular conduction, e.g. 3:1 or 4:1 block.

Atrial flutter with 1:1 conduction can occur due to sympathetic stimulation or in the presence of an accessory pathway — especially if AV-nodal blocking agents are administered to a patient with WPW.

Atrial flutter with 1:1 conduction is associated with severe haemodynamic instability and progression to ventricular fibrillation.

Question 5

atrial fibrillation

Answer 5

rate: variable, depending on ventricles
rhythm: irregularly-irregular
p wave: none, chaotic atrial activity
P:QRS ratio: none
PR interval- none
qrs widtch: <120 ms (0.12 seC)

• > QRS complexes usually < 120 ms unless pre-existing bundle branch block, accessory pathway, or rate related aberrant conduction.
• > Fibrillatory waves may be present and can be either fine (amplitude < 0.5mm) or coarse (amplitude >0.5mm).
• > Fibrillatory waves may mimic P waves leading to misdiagnosis.

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Atrial Fibrillation in WPW