Avnrt - AV Nodal Reentrant Tachycardia (AVNRT)- Case Study
AV Nodal Reentrant Tachycardia (AVNRT) is an arrhythmia caused by dual AV nodal pathways (one slow and one fast conduction route that enters the AV node). The fast tract has rapid conduction speeds with a longer refractory period, while the slow tract has slower conduction speeds with a shorter refractory period. During sinus rhythm, both pathways are activated, but the fast pathway makes it through the AV node quicker, activating the His bundle and simultaneously retrogradely entering the slow pathway, preventing it from having any further effect (Figure 1).
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
- 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.