Is this narrow complex narrow complex tachycardia with short RP interval likely to be AVRT or AVNRT?

We can see a retrograde P wave well away from the QRS, in the ST segment. This is more likely to be AVRT. In AVNRT, P is either not seen as it is buried in the QRS or it is seen at the end of the QRS causing a pseudo R’ or S.

Try to think of a diagnosis before scrolling down for the answer.

The ECG shows atrial fibrillation with Ashman phenomenon.

The RR interval is long between the first and second beats. This causes the effective refractory period of the right bundle to be longer than normal causing RBBB aberrancy as the third beat has come at a short RR interval thus falling within this ERP. Note that in spite of coming at a short RR interval, the fourth beat is not having aberrancy as the preceding RR is short (hence ERP is not increased after the third beat).

Before scrolling down, try to think of the possible diagnoses for this ECG.

This ECG shows a regular narrow complex tachycardia at a rate of 140/min.

It is a long RP tachycardia with superior P axis.

The possibilities are-

• Fast-slow AVNRT (slow retrograde conduction in an AVNRT)
• PJRT (slow retrograde conduction in an AVRT)
• Ectopic atrial tachycardia (focus near AV node)

Evidently, this patient has LBBB. The question is whether there is MI or not. Scroll down for the discussion after you have formed your opinion about the issue.

The criteriae derived from the GUSTO I study to diagnose MI in the presence of LBBB are-

• Discordant ST elevation of 5 mm
• Concordant ST elevation of 1 mm and
• Concordant ST depression of 1 mm (applicable only in v1 to v3).

Now take a look at the ECG again and then scroll down.

In the present ECG, v2 shows discordant ST elevation of more than 5 mm and v5 shows concordant ST elevation of 1 mm. Thus there is MI.

Diagnosis-

Torsades de pointes.

Diagnosis- Indeterminate axis.

The second QRS in each lead is a ventricular premature beat and should not be considered for axis analysis.

The QRS complexes are equiphasic in all precordial leads. So the frontal plane QRS axis cannot be determined.

Click on image to enlarge.

Diagnosis- Ectopic atrial rhythm.

Pointers- Negative P waves in II, III and aVF. Positive P wave in aVR. P wave axis is around – 105 degrees.

Click on the image to enlarge.

An enlarged view of v1 is shown below.

Diagnosis- Sine waves in hyperkalemia.

Courtesy- Dr Anoop Parameswaran MD MPH.

Click on image to enlarge.

Diagnosis- Right ventricular hypertrophy.

Courtery- Dr Anoop Parameshwaran MD MPH.

Click on image to enlarge.

Diagnosis- Dextrocardia.

Pointers-

1. P axis is 120 degrees.
2. QRS axis is 165 degrees.
3. QRS voltages decrease from v1 to v6.

Courtesy- Dr Anoop Parameswaran MD MPH.