Image Based Question-67098

Correct Answer » B Explanation

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