Variants of accessory pathways.

Variant accessory pathways include atriofascicular, nodofascicular, nodoventricular, atrio-Hisian, and fasciculoventricular pathways. Atriofascicular pathways are the most common with others occurring rarely. The anatomical descriptions, electrocardiographic findings, electrophysiologic findings, and clincial manifestations are discussed.

Unusual variants of pre-excitation: From anatomy to ablation: Part III-Clinical presentation, electrophysiologic characteristics, when and how to ablate nodoventricular, nodofascicular, fasciculoventricular pathways, along with considerations of permanent junctional reciprocating tachycardia.

The recognition of the presence, location, and properties of unusual accessory pathways for atrioventricular conduction is an exciting, but frequently a difficult, challenge for the clinical cardiac arrhythmologist. In this third part of our series of reviews, we discuss the different steps required to come to the correct diagnosis and management decision in patients with nodofascicular, nodoventricular, and fasciculo-ventricular pathways. We also discuss the concealed accessory atrioventricular pathways with the properties of decremental retrograde conduction that are associated with the so-called permanent form of junctional reciprocating tachycardia. Careful analysis of the 12-lead electrocardiogram during sinus rhythm and tachycardias should always precede the investigation in the catheterization room. When using programmed electrical stimulation of the heart from different intracardiac locations, combined with activation mapping, it should be possible to localize both the proximal and distal ends of the accessory connections. This, in turn, should then permit the determination of their electrophysiologic properties, providing the answer to the question "are they incorporated in a tachycardia circuit?". It is this information that is essential for decision-making with regard to the need for catheter ablation, and if necessary, its appropriate site.

Can noninvasive testing identify benign patterns of suggested pre-excitation on electrocardiogram?

BACKGROUND: The presence of anterograde conduction through an accessory pathway (AP) has been linked to sudden cardiac death. Unfortunately, pre-excitation associated with classic pathways can be difficult to differentiate from benign APs such as nodofascicular fibers. OBJECTIVE: Identifying characteristics on electrocardiogram (ECG) and exercise that differentiate classic and benign AP connections in suggested pre-excitation patterns. METHODS: Retrospective review of patients presenting between 1995 and 2017 with ventricular pre-excitation on ECG, determined to have either typical left-lateral AP during electrophysiology study (EPS), or benign, or no AP determined by either transesophageal electrophysiology study (TEP), or EPS. RESULTS: A total of 96 patients were included, 14.2 years (4-24), 45% female, 90% Caucasian. Of these, 60 (63%) had a classic APs identified on EPS and 58 (97%) underwent successful ablation. Conversely, 36 (37%) had benign pathways identified. ECG findings differed between the groups: PR-interval 102 versus 120 ms (P < .0001), QRS-duration 110 versus 102 ms (P < .0001), QRS-axis 74 versus 59 degrees (P = .0005), and QRS onset to peak R/S in limb leads 64 versus 42 ms (P < .0001), and precordial leads 66 versus 46 ms (P < .0001). Change in QRS duration during exercise differed between the groups: 25 versus 2 ms (P < .0001) and ECG characteristics identified the presence of an AP with 97% sensitivity and 94% negative predictive value. CONCLUSION: Classic and benign APs exhibit different ECG characteristics, though clinical overlap does not allow for absolute differentiation. These data may help with risk stratification decision making though does not obviate the need for additional invasive testing.

Prevalence and characteristics of atrioventricular nodal reentrant tachycardia with a bystander concealed nodoventricular/nodofascicular pathway.

BACKGROUND: The concealed nodoventricular/nodofascicular (NV/NF) pathway is mostly a bystander, retrograde bypass tract connecting right ventricle/right bundle branch (RBB) and slow pathway (SP), which is observed in patients with atrioventricular nodal reentrant tachycardia (AVNRT). However, its prevalence and characteristics in response to pacing maneuvers have not been fully evaluated. OBJECTIVE: This study investigated the prevalence and characteristics of AVNRT with a bystander NV/NF-pathway. METHODS: We retrospectively reviewed 153 consecutive patients undergoing catheter ablation of AVNRT. Excluding 52 patients with inadequate electrophysiological data, 101 patients composed the study population. RESULTS: Three patients (3.0%) had bystander concealed NV/NF-pathways, all of which were connected to the SP. The tachycardia was typical SP/fast pathway (FP) AVNRT in two patients and atypical FP/SP AVNRT in one patient. In all cases, His-refractory ventricular extra stimuli (VESs) reset the AVNRTs with delay through the NV/NF-pathways. Ventricular overdrive pacing (VOP) in the early-phase also reset the AVNRT with delay. Earlier VESs and middle-phase of VOP did not reset the tachycardia, and further earlier VESs and late-phase of VOP reset the tachycardia with advance through the RBB-His conduction. CONCLUSION: A bystander NV/NF-pathway was not rare in patients with AVNRT. The VESs and VOP for the AVNRTs with the bystander NV/NF-pathways were characterized by the two-phase resetting phenomenon: initial transient resetting with delay through the NV/NF-pathway, and late resetting with advance through the RBB-His conduction.

Ventriculoatrial Block and His-His Changes During Supraventricular Tachycardia: Diagnostic and Mechanistic Implications.

Supraventricular tachycardia (SVT) with ventriculoatrial (VA) block can represent a diagnostic challenge. We present a case of SVT where His-His interval shortening was repeatedly observed during episodes of VA block. This novel observation is more diagnostically suggestive of atrioventricular nodal re-entrant tachycardia, as opposed to orthodromic re-entry using a nodofascicular or nodoventricular pathway where a constant His-His is recorded during episodes of VA block. (Level of Difficulty: Intermediate.).

The various manifestations of concealed nodofascicular/nodoventricular bypass tracts.

BACKGROUND: The various arrhythmic manifestations of concealed nodofascicular (NF)/nodoventricular (NV) bypass tracts (BPTs) are poorly understood. OBJECTIVE: The purpose of the study was to define diagnostic criteria for supraventricular tachycardias (SVTs) associated with concealed nodal pathways (NPs). METHODS: We reviewed 11 patients with concealed NPs who underwent electrophysiology study and ablation for symptomatic SVT. RESULTS: Of 11 patients 7 (64% women; mean age 54 ± 16 years), NF/NV BPTs were active bystanders during atrioventricular nodal reentrant tachycardia (atypical [n = 4]; typical [n =2]) or participants during orthodromic NF/NV reentrant tachycardia (n = 5). The majority (10 of 11 [91%]) had nodal origin in the slow pathway (SP) and 7 of 11 (64%) presented as long RP SVT. Ablation of the SP targeting the right (n = 10) or left (n = 1) inferior extension eliminated concealed NP-associated SVTs in all patients. CONCLUSION: Concealed NF/NV BPTs are active bystanders equally as common as participants during SVT. They typically insert into the SP and often present as long RP SVT. SP ablation eliminates concealed NF/NV BPT-associated SVTs regardless of the mechanism.