الفهرس 
COVEROnly 14 pages are availabe for public view
 |  | from | 170 |  |  |
| | | from | 170 | | |
Abstract
Supraventriculat tachycardias are a prevalent tachycardia among healthy individuals; having different electrophysiologic mechanisms.
AVNRT is now known to occur with eccentric atrial activation and, in addition, decremental septal pathways may mimic AVNRT especially of the fast-slow or slow–slow forms. Septal pathways may have the property of decremental conduction and normal atrial retrograde activation during tachycardia.
Few patients with dual AV node physiology have orthodromic reciprocating tachycardia. In addition, evidence of an accessory pathway doesn’t guarantee that orthodromic reciprocating tachycardia is the tachycardia mechanism. Patients with preexcitation may have AV nodal reentry. Therefore, it may be remembered that dual AV nodal pathways and accessory pathways can be incidental findings.
Distinguishing AVNRT from ORT is often straight forward, because an eccentric atrial activation sequence strongly favored ORT. However distinguishing AVNRT from ORT using a septal accessory pathway may be more problematic because a concentric atrial activation sequence is present in both.
Differentiating (AVNRT) from orthodromic (AVRT) was an essential step in the diagnosis of (SVT).
The objective of this study was to demonstrate the benefit of the response to Para-Hisian pacing (capture and loss of capture of HB-RB); to differentiate AVNRT from ORT (mainly concealed septal accessory pathway).
This study included twenty patients with narrow complex supraventricular tachycardia; proved by surface ECG and referred for diagnostic electrophysiological study and radiofrequency ablation.
Patients were excluded from this study if the following tachycardias were met: atrial flutter, atrial fibrillation, multifocal atrial tachycardia, SA reentrant tachycardia, concomitant AVNRT and AVRT, manifest WPW with surface ECG showing signs of preexcitation suggestive of antegrade conducting accessory pathway and left free wall accessory pathway.
All Patients Were Subjected to the Following:
Patients given informed consent for electrophysiologic study.
Full medical history, clinical examination and risk factor documentation.
12 lead resting ECG and during tachycardia.
Basic electrophysiologic study; to interpret the mechanism of tachycardia and to induce it.
The test of the study: Pacing while withdrawing from anterobasal right to His bundle catheter until the width of the QRS complex narrowed indicating direct HB-RB capture the pacing output and pulse width were then decreased until the paced QRS complex lenghthened indicating loss of HB-RB capture. The pacing output was increased and decreased to gain or lose HB-RB capture respectively.
Study test wasn’t performed after ablation of AP due to either VA dissociation or retrograde whenchebach block denoting no residual AP and no AVN conduction after ablation.
Based on electrophysiological study the study population was subdivided into two groups:
Group A: This group included 10 patient having AVNRT.
Group B: This group included 10 patients with orthodromic AVRT due to concealed accessory pathway with no change in S-A with loss of HB-RB capture (group B1, n=7) or slight change in S-A with loss of HB-RB capture (group B2, n=3).
The present study demonstrated significant discrepancy between the two groups on the topic of the difference of S-A interval during capture of HB-RB and S-A interval during non capture of HB-RB.
The change in the S-A interval intervals measured during capture of HB-RB and non capture of HB-RB was significantly different in (group A), there was no change in group (B1) and slight lenghthening with constant V-A interval in group (B2).
So the present study was clarifying the inquiry of this test in differentiating between patients with AVNRT and patients between ORT using concealed septal accessory pathways and to assess persistence of conduction over the accessory pathway after ablation or wether residual retrograde AVN conduction was present after ablation.