Atrial flutter, 4:1 conduction
A calcium-channel blocker makes the lower level of the AV node block every second wave the upper level passes. Every fourth flutter wave conducts: flutter at 300 and a regular ventricular rate of 75.
On the trace
- Measure the ventricular rate. 75 per minute, regular, R-R 800 ms.
- Count the flutter waves between two QRS complexes in II. Three are in plain view. The fourth is in the QRS.
- Measure the flutter cycle. 200 ms: 300 per minute, the same flutter as at 2:1. The drug acts on the AV node, not on the circuit.
- Look for the T. The flutter waves run through it, so its shape changes from lead to lead and its end cannot be found. The readout shows no QT.
- Measure the QRS. 96 ms, narrow.
Telling it apart
| 2:1 | 4:1 | |
|---|---|---|
| Flutter rate | 300 | 300 |
| Ventricular rate | 150 | 75 |
| Flutter waves for each QRS | Two | Four |
| Sawtooth | Partly hidden | Easy to see |
What it means
A slow, regular ventricular response in flutter usually means an AV nodal drug, here a calcium-channel blocker. It depresses the lower level of the AV node, which then blocks every second wave the upper level passes. The flutter itself continues: the rate is controlled, the rhythm is not converted.
Full articleAtrial FlutterHow to recognise it, why it happens, what it means and what to do.