What is the correct answer and explain it in easy terms
The correct answer is D. Atrial flutter with 2:1 block.
Here's why, in plain terms:
What you see on this ECG:
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Fast, regular "sawtooth" waves - Look at leads VF (aVF) and V1/V2/V3. Instead of normal rounded P waves before each heartbeat, you see rapid, repetitive zigzag waves that never return to a flat baseline. These are called flutter waves (or "F waves"). They occur at ~300 beats/minute in the atria.
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2:1 ratio - For every 2 flutter waves, only 1 QRS complex (the tall spike = actual heartbeat) gets through to the ventricles. The AV node acts as a gatekeeper and blocks every other signal. So the ventricular rate is ~150 bpm (300 ÷ 2 = 150).
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Rate of ~150 bpm with regular rhythm - This is a classic clue. Anytime you see a regular tachycardia at exactly ~150 bpm, think "atrial flutter with 2:1 block" first.
Why not the others?
| Option | Why it's wrong |
|---|---|
| A. Paroxysmal SVT | SVT also gives ~150 bpm but has normal P waves (or no visible P waves), not sawtooth flutter waves |
| B. Paroxysmal VT | VT has wide, bizarre QRS complexes (broad spikes). Here the QRS complexes look narrow and normal |
| C. Sinus tachycardia | Sinus tachy has clear individual P waves before each QRS, and rarely exceeds ~150 bpm. No sawtooth pattern |
The simple memory trick:
"Regular rate of 150 bpm + sawtooth baseline = Atrial flutter with 2:1 block until proven otherwise."
The atria are firing like a machine gun at 300/min, but thankfully the AV node only lets every 2nd signal through, keeping the heart rate at a manageable (but still fast) 150 bpm.
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