Atrial flutter in lamin cardiomyopathy Michael C Y Nam, MD PhD,Paul B Sparks. MD PhD.Department of Cardiology,Royal Melbourne Hospital,300 Grattan Street,Parkville,Victoria 3050,AustraliaCorresponding author:Michael Chi Yuan NamT: +61393427000E: dr.michael.nam@gmail.comDeclarations of interest: noneFunding: NoneCase PresentationA 40-year-old man with genotype-positive lamin cardiomyopathy attended the EP lab for atrial flutter ablation. He had previously developed AV block and received a dual chamber implantable cardiac defibrillator (ICD) due to presence of significant mid-wall ventricular septal fibrosis seen on cardiac magnetic resonance imaging. He had also undergone successful cavotricuspid isthmus ablation for typical atrial flutter 2 years prior. His cardiomyopathy had progressed, with transthoracic echocardiogram whilst in atrial flutter showing severe LV dilatation with moderate left ventricular systolic dysfunction. Both atria were also severely dilated. His presentation ECG was thought to be consistent with clockwise CTI dependent atrial flutter with reconnection across the cavotricuspid isthmus. However, the atrial flutter appearance was different on presentation to the EP lab (figure 1).Insertion of multipolar EP catheters inserted via the right femoral vein revealed a vertical intracardiac electrogram activation along the coronary sinus (CS) with approximate tachycardia cycle length (TCL) of 240ms (figure 1). Entrainment mapping in combination with 3-D electroanatomical mapping (CARTOTM 3 version 7, Biosense Webster, Irvine, California) was performed to identify tachycardia mechanism and localise the circuit. Proximal CS, Distal CS, and lateral right atrium (RA) were remote to the circuit. Entrainment at the anterior SVC/RA junction and septum were ‘in’, confirming an upper RA reentrant circuit mechanism. During mapping of the upper anteroseptal region, long fractionated signals were seen on the ablation catheter encompassing greater than 50% of the entire TCL seen on both bipoles of the ablation catheter (figure 2). Entrainment confirmed this location to be within the circuit. Catheter pressure during mapping of this region repeatedly terminated the atrial flutter. Differential pacing during sinus rhythm confirmed persistent cavotriscupid isthmus block from the original procedure. The current clinical atrial flutter was easily reinducible with atrial burst pacing from the CS. Patchy regions of low voltage and double electrogram potentials were seen extending adjacent to these complex signals, thereby delineating a channel for reentry. Activation mapping identified the entire TCL within this region. What is the tachycardia mechanism and subsequent ablation strategy?Commentary:The combination of activation and entrainment mapping produced findings consistent with a localised reentrant circuit at the right atrial septum. Therefore the ablation strategy was to create a lesion set at the superior aspect of the circuit starting at the region of electrogram fractionation and extending up to the SVC-RA junction. However, upon delivering the first ablation lesion, there was sudden electrical isolation of the lateral right atrium evidenced by independent electrical activity on a duodecapolar catheter positioned on the lateral RA, and the commencement of atrial pacing from the ICD despite ongoing atrial flutter seen on the CS catheter (figure 3). The anteroseptal RA was still actively within the flutter circuit confirmed by repeat entrainment but catheter pressure to the region of long fractionated low amplitude signals resulted in atrial flutter termination. Further ablation was delivered to complete the line of block to the SVC. Atrial flutter was no longer inducible after completion of the line. The procedure was discontinued at this point given low left atrial appendage filling pressures. The patient subsequently underwent left atrial appendage ligation, epicardial left ventricular pacing implantation, and referral for heart transplantation.Lamin cardiomyopathy is a rare inherited cardiac condition associated with malignant ventricular arrhythmia due to the development of patchy fibrosis characteristic with disease progression (1). Importantly, electrical remodelling and development of arrhythmic substrate appears to occur early in the disease, which may explain why sudden cardiac death often precedes clinical heart failure in this patient population (2). Emerging studies report that such remodelling is not confined to the ventricle, with one group observing extensive atrial scar and slow conduction in their case series of atrial fibrillation ablation in this patient cohort (3). In addition to widespread low voltage in the left atrium prior to ablation and poor long-term procedural success rates, they also reported profound delay in interatrial conduction with spontaneous intraprocedural left atrial appendage dissociation. There have been no reports of segmental RA isolation with a single RF lesion, which reflects the random and extensive nature of endocardial scarring in this form of heart disease. In this case, high density mapping was not performed due to repeated tachycardia termination caused by catheter pressure requiring atrial burst pacing to reinduce. Nonetheless, limited point-by-point combined with entrainment mapping adequately confirmed tachycardia circuit location and provided an ablation strategy. Isolation of the lateral RA from the remaining atria during the first RF lesion of atrial flutter serves as an important reminder that lamin cardiomyopathy results in progressive electrical remodelling of all cardiac chambers.