September 16, 2015

A non-traditional way of looking at an arrhythmia

A patient complaining of palpitations.

Image 1

The full disclosure strip shows a regular narrow complex tachycardia at a rate of about 130 bpm. This can be a supraventricular tachycardia (SVT). Simplistically speaking, SVT can be any tachyarrhythmia with the driving impulse above the AV node. This can be sinus tachycardia (ST), atrial tachycardia (AT), atrial flutter (AFl), junctional tachycardia (JT),AV nodal reentry tachycardia (AVNRT) or AV reentry tachycardia (AVRT).

The P waves are difficult to see. If you look closely at leads II, III and aVF, there are distortions in the latter part of the T waves. Yes, those are P waves. This distortion is upright in these leads. It means, we can eliminate AVNRT and AVRT. This is because AVNRT and AVRT will generate negative P waves and not positive (Image 2).We can also eliminate junctional tachycardia because JT will also generate negative P waves (or no P waves). Sometimes in JT you cannot see the P wave because ventricular activation can occur at the same time as atrial activation.

Image 2 – AVNRT and AVRT diagram

We are left with sinus tachycardia, atrial flutter and atrial tachycardia. Here a telemetry function comes in handy. The heart rate histogram or the heart rate trend graph will help differentiate. sinus tachycardia will have a graph that will show gradual increase and decrease in the heart rate (Image 3).

Image 3 – Sinus Tachycardia Heart Rate Trend

In this case, the heart rate trend is “flat” (Image 4).

Image 4 – Heart Rate Trend of the case

A tachycardia that will give a “flat” heart rate trend with upright P waves can be atrial flutter and atrial tachycardia (AT). In AFl the P waves can be upright in II, III and aVF if the it is a clockwise AFL. This tachycardia has a 2:1 AV conduction. The atrial rate of about 260 bpm is the upper end of atrial tachycardia and the lower end of atrial flutter. I would like to bring you the thoughts of Drs. Das and Zipes in their book Electrocardiography of Arrhythmia which is a great book for reference –

“Atrial tachycardia (AT) is defined as a regular atrial rhythm originating from the atrium at 100 bpm to 240 bpm. The presence of an atrial rate above 100 bpm with three different P wave morphologies signifies different foci of atrial depolarization and is called a multifocal atrial tachycardia (MAT). Previous classifications of AT had been based exclusively on the routine electrocardiogram (ECG) with a constant rate and an isoelectric line between the two consecutive P waves. Atrial flutter (AFL) is typically a reentrant arrhythmia defined as having a pattern of regular tachycardia with a rate above 240 bpm without an isoelectric baseline between deflections. The typical (cavotricuspid dependent) AFL usually shows sawtooth pattern in inferior ECG leads. ATs can also have a reentrant mechanism, usually seen around a scar in the atrium. The ECG pattern can mimic an atypical (noncavotricuspid dependent) AFL. However, neither rate nor lack of isoelectric baseline is specific for any tachycardia mechanism. A rapid AT in a scarred atrium can mimic AFL, and, on the other hand, a typical AFL can show distinct isoelectric intervals between flutter waves, in diseased atria, or in the presence of antiarrhythmic drug therapy. Therefore it becomes a matter of semantics to define an AT or an atypical AFL.”

After years of just watching arrhythmias, I already know that this is atrial flutter vs. atrial tachycardia. To convince others, you need an AV blocking drug or a properly-timed PVC to expose those extra P waves .


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