Avnrt - AV Nodal Reentrant Tachycardia (AVNRT)- Case Study

During a PAC, AV nodal conduction circumstances can change compared to conduction during sinus rhythm. AV nodal conduction during sinus rhythm is shown in Figure 1, left image. When a PAC occurs in a patient with dual AV nodal conduction, a PAC can be prevented from conducting to the AV node via the fast tract because of its heightened refractoriness. As a consequence, the PAC impulse uses the less refractory slow pathway through the AV node (Figure 1, center image). The first clue that this is happening is the ECG shows the PAC resulting in a much longer PR interval than would occur during sinus rhythm. Sometimes this is called a “PR jump,” for example, as shown in Case #1.

Figure 1: AVNRT Pathophysiology

Identifying AVNRT:

• Initiated by a PAC with a prolonged PR interval
• P-wave transitions from pre-QRS to buried in or behind it (pseudo s wave)
• P:QRS ratio = 1:1*
• Regularity = Regular
• Rate = > 100 bpm (usually, but in the extreme elderly, 90+, it can be

AVNRT Case Study #1

33-year-old female with a long history of palpitations heretofore not diagnosed. The following three strips show onset, maintenance, and offset of one of the 12 episodes experienced.  

Example Strip #30

AVNRT onset. The R-R plot to the left is used to demonstrate the change in the heart rate pattern from sinus to AVNRT where there is a jump in heart rate of ~100 bpm. After ~2 minutes of AVNRT, the R-R plot shows a return to NSR. The two red dots in the middle of the R-R plot show when the patient pushed her button, indicating her perception of an arrhythmia before for the 40-minute period. The near-field view shows the transition from sinus rhythm followed by the PAC with a prolonged PR interval. Following the PAC, there is a transition into AVNRT with a retrograde P-wave seen at the terminus of QRS.

Example Strip #31

This strip shows the fastest area of this run of AVNRT.

Example Strip #33

Below, AVNRT offset is ending with a retrograde P-wave (blue arrow) and the return of sinus rhythm.

AVNRT Case Study #2

64 year-old male with a long-standing history of palpitations

Example Strip #18

This run of AVNRT begins after a 4-beat run of AT. The R-R plot shows an abrupt change in heart rate. The near field view (8-second ECG tracing) depicts sinus rhythm followed by AT with the last ectopic atrial beat landing immediately before the last QRS of the AT run. This last atrial beat led to a long PR and then the first echo beat and a clear inverted retrograde P-wave at the end of the QRS.

Example Strip #21

This strip shows the continuation of the previous AVNRT onset strip.

Example Strip #32

This strip shows the termination of AVNRT. First, notice the sudden change in the R-R rate pattern. On the ECG tracing, a PVC couplet retrogradely enters the AV node, thereby interrupting the re-entrant loop with a return to sinus rhythm.

AVNRT Case Study #3

63-year-old female with a history of tachycardia.

Example Strip #4

In this strip, the R-R plot shows the sudden increase in heart rate characteristic of the onset of AVNRT. Note that it is not a fixed rate but changes over time. This is also characteristic of AVNRT; it rarely is a constant rate. The red dot on the R-R plot shows that the patient became aware of the arrhythmia about one minute after it started. Onset of AVNRT is a consequence of a 4-beat run of AT. After AVNRT onset, there is a change in P-wave placement to behind the QRS complexes. Unlike the example in Case #2, the retrograde P-wave is a modest distortion of the terminus of the QRS with a slight upward vector. Whether this retrograde P-wave is positive or negative will depend upon the relative location of the patch to the atria and ventricles.

Example Strip #12

This R-R plot shows a sudden drop in heart rate indicative of AVNRT termination. The 8-second ECG tracing shows consistent retrograde P-waves at the terminus of the QRS. The arrhythmia’s offset is preceded by a single PAC, followed by a 3-beat run of ventricular tachycardia and then a return to sinus rhythm.