Background: The diagnostic work-up for cardiac arrest from ventricular tachyarrhythmias occurring in younger adults and structurally normal hearts is variable and often incomplete. Methods: We reviewed records for all recipients of a secondary prevention implantable cardiac defibrillator (ICD) younger than 60 years at a single quaternary referral hospital from 2010-2021. Patients were included if they had unexplained ventricular arrhythmias (UVA) and absence of structural heart disease on echocardiogram, normal coronary assessment and no clear diagnostic features on ECG. We specifically evaluated the adoption rate of five modalities of ‘second-line’ cardiac investigations: cardiac magnetic resonance imaging (CMR), exercise ECG, flecainide challenge, electrophysiology study (EPS) and genetic testing. We also evaluated patterns of anti-arrhythmic drug therapy and device-detected arrhythmias and compared them with secondary prevention ICD recipients with a clear aetiology found on initial assessment. Results: 102 recipients of a secondary prevention ICD under the age of 60 were analysed. 39 patients (38.2%) were identified with UVA and were compared with the remaining 63 patients with VA of clear aetiology (61.8%). UVA patients were younger (35.6 ± 13.0 years vs 46.0 ± 8.6 years, p<0.001) and were more often female (48.7% vs 28.6%, p=0.04). CMR was performed in 32 patients with UVA (82.1%), whereas flecainide challenge, stress ECG, genetic testing and EPS were only performed in a minority of patients. Overall, the use of a second-line investigation suggested an aetiology in 17 patients with UVA (43.5%). Compared to patients with VA of clear aetiology, UVA patients had lower rates of antiarrhythmic drug prescription (64.1% vs 88.9%, p=0.003) and had a higher rate of device-delivered tachy-therapies (30.8% vs 14.3%, p=0.045). Conclusion: In this real-world analysis of patients with UVA, the diagnostic work-up is often incomplete. While CMR was increasingly utilized at our institution, investigations for channelopathies and genetic causes appear to be underutilized. Implementation of a systematic protocol for work-up of these patients requires further study.

The exponential rise in the incidence of peri-mitral flutter has paralleled the increasing use of more extensive atrial substrate ablation for atrial fibrillation (AF). Given the relative paucity of randomised evidence to support its role in AF management, mitral isthmus ablation should largely be reserved for patients with peri-mitral flutter. Catheter ablation for peri-mitral flutter is challenging due to complex anatomic relationships. The aim of this report is to review the anatomic considerations and approaches to catheter ablation for peri-mitral flutter.

Background: Catheter ablation is highly effective for AVNRT. Generally junctional rhythm(JR) is an accepted requirement for successful ablation however there is a lack of detailed prospective studies to determine the characteristics of JR and the impact on slow pathway conduction. Methods: Multicentre prospective observational study evaluating the impact of individual radiofrequency(RF) applications in typical AVNRT(Slow/Fast). Characteristics of JR during ablation were documented and detailed testing was performed after every RF application to determine outcome. Procedural success was defined as ≤1 AV nodal echo. Results: Sixty-seven patients were included(mean age 53±18years, 57% female and a history of SVT 2.9±4.7years). RF(50w,60degrees) ablation for AVNRT was applied in 301 locations with JR in 178(59%). Successful slow pathway modification was achieved in 66(99%) patients with slow pathway block in 30(46%). Success was associated with JR in all patients. Success was achieved in 6 patients with RF<10 seconds. There was no significant difference in the CL of JR during RF between effective(587±150ms) vs ineffective (611±193ms,p=0.4) applications. Inadvertent JA-block with immediate termination of RF was observed in 19(28%) patients with AVNRT no longer inducible in 14(74%). Freedom from SVT was achieved in 66(99%) patients at a mean follow up of 15±6 months. Conclusion: In this prospective study, JR was required during RF for acute success in AVNRT. Cycle length of JR during RF was not predictive of success. Unintended JA block during faster JR was associated with slow pathway block. RF applications as short as 10s resulting in junctional rhythm may be successful in some patients.