Atrioventricular Conduction: Physiology and Autonomic Influences.

Atrioventricular (AV) nodal conduction is decremental and very prone to alterations in autonomic tone. Conduction through the His-Purkinje system (HPS) is via fast channel tissue and typically not that dependent on autonomic perturbations. Applying these principles, when the sinus rate is stable and then heart block suddenly occurs preceded by even a subtle slowing of heart rate, it typically is caused by increased vagal tone, and block occurs in the AV node. Heart block with activity strongly suggests block in the HPS. Enhanced sympathetic tone and reduced vagal tone can facilitate induction of both AV and atrioventricular node reentry.

Electrocardiography of Atrioventricular Block.

Delayed atrioventricular (AV) conduction most commonly occurs in the AV node, resulting from AH prolongation on an intracardiac electrocardiogram and PR prolongation on a surface electrocardiogram. AV conduction may be blocked in a 2:1 manner, with a normal PR interval and wide QRS suggesting infranodal disease, whereas a prolonged PR interval and narrow QRS are more suggestive of AV nodal disease. Block within the His is suspected when there is 2:1 AV block with normal PR and QRS intervals. Complete heart block occurs when the atrial rhythm is totally independent of a junctional or lower escape rhythm.

Prophylactic Colchicine After Radiofrequency Ablation of Atrial Fibrillation: The PAPERS Study.

BACKGROUND: Pericarditis is common after radiofrequency ablation for atrial fibrillation (AF). OBJECTIVES: Study investigators hypothesized an empirical post-AF ablation treatment protocol with colchicine may reduce the incidence and severity of pericarditis. PAPERS (Post-Ablation PEricarditis Reduction Study) aimed to quantify the risks and benefits associated with prophylactic use of colchicine to prevent pericarditis following AF ablation. METHODS: PAPERS is a multicenter, prospective, randomized controlled study. Patients were randomized on the day of the procedure to receive no postprocedure prophylaxis (group A; standard of care arm) or colchicine 0.6 mg orally twice daily for 7 days starting immediately post-procedure (group B; study arm). All participants underwent a follow-up survey at 14 days postoperatively. The primary endpoint was the development of clinical pericarditis within 2 weeks following ablation. Secondary outcomes included the incidence of pericarditis by ablation type and medical therapy. RESULTS: Among 139 patients enrolled, 66 were randomized to standard of care (group A), and 73 patients were randomized to the colchicine arm (group B). The primary outcome of clinical pericarditis was reached in 7 of 66 (10.6%) patients in group A and in 7 of 73 (9.6%) patients in group B (P = 0.84). The rate of gastrointestinal discomfort was 10 of 66 (15%) in group A and 34 of 73 (47%) in group B (P < 0.001). There was an increased incidence of pericarditis in patients who underwent cavotricuspid isthmus ablation (17 of 50; 34%) in addition to pulmonary vein isolation (6 of 69; 8.7%; P = 0.001). CONCLUSIONS: Prophylactic colchicine therapy initiated after the ablation procedure in patients with AF did not affect the incidence of post-ablation pericarditis and was associated with an increased incidence of gastrointestinal side effects.

Ripple mapping in ventricular tachycardia substrate mapping and ablation of nonischemic ventricular tachycardia.

INTRODUCTION: Substrate-based ablation for ventricular tachycardia (VT) using Ripple map (RM) is an effective treatment strategy for patients with ischemic cardiomyopathy but has yet to be evaluated in patients with nonischemic cardiomyopathy (NICMO). The aim of this study is to determine the feasibility and effectiveness of an RM-based ablation for NICMO patients. METHODS AND RESULTS: This was a single-center, retrospective study including all NICMO patients undergoing VT ablation at St Vincent Hospital between January 1, 2018 and January 12, 2019. Retrospective RM analysis was performed on those that had a substrate-based ablation to identify the location and number of Ripple channels as well as their proximity to ablation lesions. Thirty-three patients met the inclusion criteria and had a median age of 65 (58, 73.5) with 15.2% of the population being female, and were followed for a median duration of 451 (217.5, 586.5) days. Of these patients, 23 (69.7%) had a substrate-based ablation with a median procedural duration of 196.4 (186.8, 339) min, 1946 (517, 2750) points collected per map, and 277 (141, 554) points were within the scar. Two (8.6%) procedural complications occurred, and 7 (30.4%) patients had VT recurrence during follow-up. RM analysis revealed an average of two Ripple channels and the patients without VT recurrence had ablation performed closer to the Ripple channels: 0 (0, 4.7) versus 14.3 (0, 23.5) cm; p = .02. CONCLUSION: An RM-based substrate ablation can be performed in NICMO patients and ablation within Ripple channels is a predictor of VT freedom.

Rapid detection of isthmus block and rhythm change using local electrogram changes during complex atrial flutter ablation.

AIMS: Multiple re-entry circuits may operate simultaneously in the atria in the form of dual loop re-entry using a common isthmus, or multiple re-entrant loops without a common isthmus. When two or more re-entrant circuits coexist, ablation of an individual isthmus may lead to a seamless transition (without significant changes in surface electrocardiogram, coronary sinus activation or tachycardia cycle length) to a second rhythm, and the isthmus block can go unnoticed. METHODS AND RESULTS: We hypothesize and subsequently illustrate in three patient cases, methods to rapidly identify a transition in the rhythm and isthmus block using local electrogram changes at the ablation site. CONCLUSION: Local activation sequence changes, electrogram timing, and the behaviour of pre-existing double potentials can reveal isthmus block promptly when rhythm transitions occur during ablation of multiloop re-entry tachycardias.

Diagnostic utility of early premature ventricular complexes in differentiating atrioventricular reentrant and atrioventricular nodal reentrant tachycardias.

BACKGROUND: His-refractory premature ventricular complexes perturbing a supraventricular tachycardia (SVT) establish the presence of an accessory pathway (AP). Earlier premature ventricular complexes (ErPVCs) may perturb SVTs but are considered nondiagnostic. OBJECTIVE: The purpose of this study was to test the hypothesis that an ErPVC will always show a difference >35 ms in its advancement of the next atrial activation during atrioventricular nodal reentrant tachycardia (AVNRT). During atrioventricular reentrant tachycardia (AVRT), a PVC delivered close to the circuit can result in greater advancement of atrial activation due to retrograde conduction via an AP. Thus, an AP response, defined as ErPVC (H1S2) advancing the subsequent atrial activation (A1-A2) more than this minimum difference (A1A2 ≤ H1S2+35 ms), establishes the presence of an AP. METHODS: Sixty-five consecutive patients with SVT were retrospectively evaluated. ErPVCs were defined when the ventricular pacing stimulus was >35 ms ahead of the His during tachycardia. RESULTS: Among the 65 cases, 43 were AVNRT and 22 AVRT. Fourteen AVRT cases had an AP response with a mean H1S2+35 ms of 336 ± 58 ms and A1A2 of 309 ± 51ms. No AVNRT cases had an AP response. The specificity of an AP response to ErPVC in predicting AVRT was 100%. CONCLUSION: An AP response to PVCs (A1A2 ≤ H1S2+35 ms) is 100% specific for the presence of an AP.

Rate Control Versus Rhythm Control in Patients with Left Ventricular Assist Devices and Atrial Fibrillation.

BACKGROUND: Atrial fibrillation (AF) is a common comorbidity in patients with left ventricular assist devices (LVAD) with no defined guideline treatment strategy of rate versus rhythm control. The purpose of this study is to determine the effects of rate versus rhythm control for AF on the outcomes of patients with LVAD at our institution. METHODS: Consecutive patients who underwent LVAD implantation at St Vincent Hospital from January 1, 2015 to December 31, 2017 were retrospectively evaluated. Patients with AF were identified and divided into rate control or rhythm control groups. The primary outcome evaluated was a composite of death, heart failure admission, gastrointestinal bleed, ventricular tachycardia, cerebrovascular accident, hemolysis, and pump thrombosis. Secondary outcomes included the individual variables from the primary outcome. RESULTS: Out of 201 patients that underwent LVAD implantation, 81 had AF after implantation and were included with a median follow-up period of 384 days. The rate control group (n = 31; 38%) and the rhythm control group (n = 51; 62%) had no difference in composite outcomes (61% vs 59%, p = 0.83). When taken individually there was no difference in outcomes between the two groups. Thirteen patients underwent electrical cardioversion and successful conversion to normal sinus rhythm occurred in 71% of cases with a 60% recurrence rate. CONCLUSIONS: There was no difference in primary outcome between rate and rhythm control groups. These data suggest that maintenance of sinus rhythm may not be necessary in all patients with LVAD.

Atrioventricular Conduction: Physiology and Autonomic Influences.

Atrioventricular (AV) nodal conduction is decremental and very prone to alterations in autonomic tone. Conduction through the His-Purkinje system (HPS) is via fast channel tissue and typically not that dependent on autonomic perturbations. Applying these principles, when the sinus rate is stable and then heart block suddenly occurs preceded by even a subtle slowing of heart rate, it typically is caused by increased vagal tone, and block occurs in the AV node. Heart block with activity strongly suggests block in the HPS. Enhanced sympathetic tone and reduced vagal tone can facilitate induction of both AV and atrioventricular node reentry.

Electrocardiography of Atrioventricular Block.

Delayed atrioventricular (AV) conduction most commonly occurs in the AV node, resulting from AH prolongation on an intracardiac electrocardiogram and PR prolongation on a surface electrocardiogram. AV conduction may be blocked in a 2:1 manner, with a normal PR interval and wide QRS suggesting infranodal disease, whereas a prolonged PR interval and narrow QRS are more suggestive of AV nodal disease. Block within the His is suspected when there is 2:1 AV block with normal PR and QRS intervals. Complete heart block occurs when the atrial rhythm is totally independent of a junctional or lower escape rhythm.

Mechanism and interpretation of two-for-one response to premature atrial complexes during atrioventricular node re-entry tachycardia.

AIMS: The response to premature atrial complexes (PACs) during tachycardia has been shown to differentiate atrioventricular nodal re-entrant tachycardia (AVNRT) from focal junctional tachycardia (JT). His refractory PAC (HrPACs) perturbing the next His (resetting with fusion) is diagnostic of AVNRT and such a late PAC fusing with the native beat cannot reset the focal source of JT. Early PAC advancing the immediate His with continuation of tachycardia suggests JT but can also occur in AVNRT due to simultaneous conduction through the AV nodal fast and slow pathways [two-for-one response (TFOR)]. The objective of this study was to evaluate the incidence and mechanism of TFOR after early premature atrial complexes (ePACs) during AVNRT and to differentiate it from the known response to ePACs during JT. METHODS AND RESULTS: Typical AVNRT cases were diagnosed using standard criteria. We evaluated the responses to scanning PACs delivered during tachycardia in 100 patients undergoing AV node slow pathway modification for AVNRT. The responses to HrPACs and ePACs delivered from coronary sinus os or high right atrium were retrospectively reviewed. In 10 patients, ePACs advanced the immediate His with continuation of tachycardia. In all 10 cases, HrPACs advanced the next His, confirming AVNRT as the mechanism, and indicating a TFOR. CONCLUSION: A TFOR can occur in a small number of patients during AVNRT and is therefore not diagnostic of JT. However, HrPACs always perturbed the next His in these cases, confirming the diagnosis of AVNRT and allowing for differentiation from JT.