Long RP tachycardia includes atrial tachycardia (atrial tachycardia), atrioventricular fold tachycardia with slow conduction bypass involvement, and AV nodal fold tachycardia of the fast and slow type. The differential diagnosis is outlined as follows.
1. Judgment based on probability
Long RP tachycardia is mostly atrial tachycardia, while the latter two are rare. Therefore, if judged from only one ECG of tachycardia, it is usually diagnosed as atrial tachycardia directly, although the latter two cannot be completely excluded.
2. Judgment based on multiple ECG records in the medical history
Patients with atrial tachycardia may exhibit AV conduction at different times due to different nerve activity, stimulation of the vagus nerve, drugs that inhibit AV node conduction, etc. Atrial tachycardia with slow conduction bypass can be completely ruled out, and AV nodal tachycardia with fast and slow conduction can also be almost ruled out.
3. Judgment based on the morphological characteristics of P waves during tachycardia
If the P-wave in the inferior wall leads is upright during tachycardia, we can exclude AV nodal regressive tachycardia, because in the latter tachycardia, the fast path conduction is forward and the slow path is reverse, so the P-wave in the inferior wall leads should be negative. There are only two possibilities for long RP tachycardia with positive P waves in the inferior wall leads, namely atrial tachycardia and atrioventricular fold tachycardia with slow conduction bypass.
4.Electrophysiological labeling
Electrophysiological marker techniques are the main method for the differential diagnosis of long RP tachycardia and include many techniques.
(1) sequence of intracardiac atrial excitation
Eccentric excitation can almost exclude fast and slow atrioventricular node folding tachycardia, although there are reports of slow path exit of atrioventricular node folding tachycardia located in the left atrial lateral wall, but it is less common. Therefore, the differential diagnosis between the 3 is only required in those with a centripetal order of atrial excitation.
(2) Change in atrial excitation sequence after ventricular tachycardia pacing
If the atria are eccentrically excited during tachycardia, and if the atria are captured and the eccentric excitation remains unchanged under ventricular tachycardia, then atrial folding tachycardia is present and atrial tachycardia can be excluded.
(3) Ventricular RS2 stimulation technique during the Hirschsprung’s bundle undulator
Ventricular RS2 stimulation within the Hirschsprung’s bundle in the tachycardia is the most commonly used and easily understood differential diagnostic stimulation technique. Premature ventricular stimulation within the Hirschsprung’s bundle in the inactivity period that repeatedly affects atrial excitation (including premature atrial excitation, delayed atrial excitation, and aborted tachycardia) suggests that there is another retrograde conduction pathway between the atria and the ventricles other than the AV node Hirschsprung’s bundle pathway. The long RP tachycardia is also known as atrioventricular tachycardia with slow conduction bypass, and atrial tachycardia and AV nodal tachycardia of the fast and slow type can be excluded. Sometimes two premature stimuli are required to affect atrial excitation, and the tachycardia is sometimes not easily maintained, requiring adjunctive medications. Positive results can be influenced by the location of the bypass and the location of the ventricular pacing.
(4) Hirschsprung’s bundle stimulation
Parasternal stimulation of the Hirschsprung bundle can be different depending on the pacing voltage, with both the Hirschsprung bundle and the local ventricular myocardium being captured at higher voltages and only the ventricular myocardium at appropriate voltages. The presence of atrioventricular bypass, where atrial excitation is seen to precede Hirschsprung bundle excitation, supports the involvement of slow conduction bypass in atrioventricular fold tachycardia. Of course positive results can also be influenced by the location of the bypass.
(5) Comparison of VA intervals between ventricular apical stimulation and ventricular basal stimulation
The base is close to the atrioventricular ring and the atrioventricular bypass is located in the atrioventricular ring. If there is an atrioventricular bypass, the VA interval should be shorter when the base is stimulated than when the apical stimulus is stimulated; the base is the terminal part of the pulmonary system, and if there is no atrioventricular bypass, the VA interval should be longer than when the apical stimulus is stimulated. Again, this technique is influenced by the site of stimulation and the site of bypass, with the earliest site of atrial excitation being best when the stimulation site is adjacent to the tachycardia.
(6) Post-tachycardia response to ventricular tachycardia pacing
Atrial tachycardia is supported by an AAV relationship after cessation of ventricular tachycardia pacing, and by failure of ventricular tachycardia pacing to capture the atrial rhythm.
(7) Ventricular trailing stimulation
Progressive fusion of intraventricular drag strip stimulation supports atrial tachycardia and can exclude 2 other types of tachycardia.
(8) Location of the earliest intracardiac atrial excitation point
In the order of centripetal atrial excitation, if atrial excitation is earliest at the fast track site, fast-slow atrioventricular nodal tachycardia can generally be excluded.