Case
I have a 4 month old male who underwent VSD repair earlier today. His heart rate has been climbing all afternoon and now he is running a rate of 200. His blood pressure is soft and he has stopped peeing. The QRS complexes are narrow. I think this is some kind of SVT. I tried using adenosine. It did not slow the rhythm even slightly. If anything, he sped up with it. What do I do next?
What am I thinking?
There are three big clues from what I have heard so far, which suggests that this is not a typical reentry SVT (either atrioventricular reentry tachycardia or AV nodal reentry tachycardia).
The first is the statement that the heart rate has been “climbing” all afternoon. Reentry usually starts and stops abruptly. A gradually climbing suggests that this is not a reentry tachycardia, and is more suggestive of an automatic, focal mechanism. Abnormal automaticity is a phenomenon whereby cells other than the sinus node develop properties similar to a sinus node and can generate action potentials spontaneously. Sometimes such cells fire off beats at a rate much faster than the sinus node, thereby causing a tachycardia.
The second clue is the fact that this “SVT” did not respond to adenosine. Reentry SVT (AVRT and AVNRT) typically are terminated by blocking the AV node with adenosine. An atrial tachycardia or atrial flutter is in the differential for a narrow QRS tachycardia. However, blocking the AV node leads to transient slowing of the ventricular rate that is typically transient, and once the adenosine wears off, the ventricular rate goes back to where it used to be.
The third clue is that the QRS complex is “narrow.” A postoperative arrhythmia can be either an SVT or a VT. VT would have a broad QRS complex. A narrow QRS implies this is an SVT or a high septal VT that engages into the His bundle immediately, thereby leading to a narrow QRS. The most common arrhythmia that fits this description is JET or junctional ectopic tachycardia (also known as His bundle tachycardia in Britain and Europe).
JET is most commonly seen in infants soon after major open-heart surgery in the region of the AV node. Most authorities classify JET as an SVT, although it often has features similar to VT in that AV dissociation can be present (AV association can occur in some patients, with the P wave just after the QRS complex).
I would ask the caller to send me a copy of the 12 lead or monitor strip of the rhythm. Careful examination often reveals the dissociated P waves (see Fig. 22.1 ). In some patients, P waves can be hard to see. In such cases, it may be possible to do an ECG incorporating the atrial electrogram. Many postoperative patients come back from the OR with temporary atrial and ventricular pacing wires. Attaching one of the leads of the ECG to the atrial wire can give an atrial electrogram deflection on the ECG (see Figure 4.3 ).
