Question
A 45 year old business man presents with a feeling that his heart is racing. He also has some shortness of breath. This is his ECG. Present your diagnosis.
A. Atrial Fibrillation
B. Atrial Flutter
C. Ventricular Tachycardia
D. Ventricular Fibrillation
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Correct Answer » B Explanation |
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Ans: B. Atrial Flutter.
ECG image shows:
Atrial Flutter with 2:1 Block
- There are inverted flutter waves in II, III + aVF at a rate of 300 bpm (one per big square)
- There are upright flutter waves in V1 simulating P waves
- There is a 2:1 AV block resulting in a ventricular rate of 150 bpm
Atrial flutter
- It 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.
Classification
This is based on the anatomical location and direction of the re-entry circuit.
Typical Atrial Flutter (Common, or Type I Atrial Flutter)
- Involves the IVC & tricuspid isthmus in the reentry circuit. Can be further classified based on the direction of the circuit:
- Anticlockwise Reentry. This is the commonest form of atrial flutter (90% of cases).
Retrograde atrial conduction produces:
- Inverted flutter waves in leads II,III, aVF
- Positive flutter waves in V1 – may resemble upright P waves
Clockwise Reentry. This uncommon variant produces the opposite pattern:
- Positive flutter waves in leads II, III, aVF
- Broad, inverted flutter waves in V1
Atypical Atrial flutter (Uncommon, or Type II Atrial Flutter)
- Does not fulfil criteria for typical atrial flutter.
- Often associated with higher atrial rates and rhythm instability.
- Less amenable to treatment with ablation.
ECG changes of Atrial Flutter
General Features
- Narrow complex tachycardia
- Regular atrial activity at ~300 bpm
- Flutter waves (“saw-tooth” pattern) best seen in leads II, III, aVF — may be more easily spotted by turning the ECG upside down!
- Flutter waves in V1 may resemble P waves
- Loss of the isoelectric baseline
Fixed AV blocks
- Ventricular rate is a fraction of the atrial rate, e.g.
- 2:1 block = 150 bpm
- 3:1 block = 100 bpm
- 4:1 block = 75 bpm
Variable AV block
- The ventricular response is irregular and may mimic AF
- On closer inspection, there may be a pattern of alternating 2:1, 3:1 and 4:1 conduction ratios
