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Background: The existence of an atypical fast-slow (F/S) atrioventricular nodal reentrant tachycardia (AVNRT) including a superior (sup) pathway with slow conductive properties and an atrial exit near the His bundle has not been confirmed., Methods and Results: We studied 6 women and 2 men (age, 74 ± 7 years) with sup-F/S-AVNRT who underwent successful radiofrequency ablation near the His bundle. Programmed ventricular stimulation induced retrograde conduction over a superior SP with an earliest atrial activation near the His bundle, a mean shortest spike-atrial interval of 378 ± 119 milliseconds, and decremental properties in all patients. sup-F/S-AVNRT was characterized by a long-RP interval; a retrograde atrial activation sequence during tachycardia identical to that over a sup-SP during ventricular pacing; ventriculoatrial dissociation during ventricular overdrive pacing of the tachycardia in 5 patients or atrioventricular block occurring during tachycardia in 3 patients, excluding atrioventricular reentrant tachycardia; termination of the tachycardia by ATP; and a V-A-V activation sequence immediately after ventricular induction or entrainment of the tachycardia, including dual atrial responses in 2 patients. Elimination or modification of retrograde conduction over the sup-SP by ablation near the right perinodal region or from the noncoronary cusp of Valsalva eliminated and confirmed the diagnosis of AVNRT in 4 patients each., Conclusions: sup-F/S-AVNRT is a distinct supraventricular tachycardia, incorporating an SP located above the Koch triangle as the retrograde limb, that can be eliminated by radiofrequency ablation., (© 2015 American Heart Association, Inc.)

After entrainment pacing, the postpacing interval of a diastolic potential may be misinterpreted if the distal tip of the ablation catheter captures a remote bystander pathway adjacent to the critical isthmus of a complex reentrant circuit in a structurally diseased heart. We discuss this possible pitfall of entrainment mapping of reentrant ventricular tachycardia, observed after a healed myocardial infarction.

We describe a 77-year-old man with Wolff-Parkinson-White syndrome exhibiting double coronary sinus (CS) potentials during retrograde conduction over accessory pathway (AP). The first, low-frequency potential (DP1) was first recorded in the left posterolateral region, while the second, higher frequency signal (DP2) was recorded in a lateral-to-septal direction. The two signals were fused near the left lateral wall. Successful ablation of the AP was obtained at its ventricular insertion site in the postero-septal region. The unexpectedly delayed activation of the paraseptal RA following activation of the paraseptal left atrium (DP1) can be explained by the absence of a LA-CS musculature (CSM) electrical connection at the proximal CS, which forces a detour of the activation wavefront from LA to RA via the distal CS (DP2). This is a rare case exhibiting unique double CS potentials which unmasked the absence of a LA-CSM electrical connection at CS ostium.

We report an 18-year-old woman, who had undergone surgical repair of tetralogy of Fallot, and then underwent successful intracardiac recordings within the zone of slow conduction (ZSC) of the reentry circuit on the initiation of premature ventricular contractions (PVC) and reentrant ventricular tachycardia (VT), obtained with multielectrode basket catheter. PVC a) were caused by wavefronts of sinus cycles entering and exiting the ZSC, and b) were not repetitive because the wavefront of the PVC could not reenter the ZSC. Similarly, VT developed after delayed potentials of sinus cycles, and was sustained because the wavefront following the 1st cycle of VT was able to repetitively reenter and exit the ZSC. Thus, spontaneous changes in the conductivity of the ZSC, like an on-off switch, appeared to determine the onset and sustenance of reentrant VT.

We report a case of typical counterclockwise atrial flutter (AFL) with conduction block from right to left atrium along the coronary sinus (CS) musculature, confirmed by discontinuous CS activation sequence during pacing near the ostium and differential right atrial pacing. AFL was associated with an atypical flutter wave morphology, due to the detour of the activation wavefront from right to left atrium via alternate interatrial electrical connections, such as Bachmann's bundle, the interatrial septum, or both.

To examine the electrophysiologic characteristics of the subvalvular mitral region, we retrospectively searched for the presence of subvalvular diastolic potentials (DP) in 91 patients (mean age, 46.9 ± 16.6 years) who underwent catheter ablation of left-sided accessory pathways (AP). We detected low-amplitude (0.19 ± 0.09 mV) DP in 14 patients (15.4%), including 8 with overt preexcitation and 6 patients with concealed AP. The mean interval between ventricular electrogram and DP was 383 ± 46 ms (range, 306-475). DP were detected in 4 of 20 patients with antero-lateral, 3 of 38 with lateral, 4 of 12 with postero-lateral, 2 of 14 with posterior, and 3 of 10 patients with postero-septal AP. In 6 of 14 patients, DP were detected before ablation. In 4 of 8 patients with overt preexcitation, DP were consistently recorded after elimination of the delta wave, suggesting that they were not associated with AP conduction. In 6 of 11 patients, DP were observed during both sinus rhythm and ventricular pacing, suggesting that they were not artifacts. The electrophysiologic characteristics of clinically relevant DP around the mitral annulus suggest that, in normal human hearts, an anatomical substrate may be present around the mitral annulus.

The article discusses the case of a 77-year-old female patient who underwent radiofrequency catheter ablation of drug-refractory paroxysmal atrial flutter (AFl) with a focus on entrainment pacing and mapping. Topics include tachycardia cycle length (TCL), the postpacing interval (PPI), and far-field sensing of the essential pathway around the tricuspid annulus captured during high-output pacing.