Mechanisms Underlying Epicardial Radiofrequency Ablation to Suppress Arrhythmogenesis in Experimental Models of Brugada Syndrome.
ABSTRACT: OBJECTIVES:This study sought to test the hypothesis that elimination of sites of abnormal repolarization, via epicardial RFA, suppresses the electrocardiographic and arrhythmic manifestations of BrS. BACKGROUND:Brugada syndrome (BrS) is associated with ventricular tachycardia and ventricular fibrillation leading to sudden cardiac death. Nademanee et al. reported that radiofrequency ablation (RFA) of right ventricular outflow tract epicardium significantly reduced the electrocardiogram and arrhythmic manifestations of BrS. These authors concluded that low-voltage fractionated electrogram activity and late potentials are caused by conduction delay within the right ventricular outflow tract and that the ameliorative effect of RFA is caused by elimination of this substrate. Szel et al. recently demonstrated that the abnormal electrogram activity is associated with repolarization defects rather than depolarization or conduction defects. METHODS:Action potentials (AP), electrograms, and pseudoelectrocardiogram were simultaneously recorded from coronary-perfused canine right ventricular wedge preparations. Two pharmacological models were used to mimic BrS genotype: combination of INa blocker ajmaline (1 to 10 ?M) and IK-ATP agonist pinacidil (1 to 5 ?M); or combination of Ito agonist NS5806 (4 to 10 ?M) and ICa blocker verapamil (0.5 to 2 ?M). After stable induction of abnormal electrograms and arrhythmic activity, the preparation was mapped and epicardial RFA was applied. RESULTS:Fractionated low-voltage electrical activity was observed in right ventricular epicardium but not endocardium as a consequence of heterogeneities in the appearance of the second upstroke of the epicardial AP. Discrete late potentials developed as a result of delay of the second upstroke of the AP and of concealed phase 2 re-entry. Epicardial RFA of these abnormalities normalized Brugada pattern and abolished arrhythmic activity, regardless of the pharmacological model used. CONCLUSIONS:Our results suggest that epicardial RFA exerts its ameliorative effect in the setting of BrS by destroying the cells with the most prominent AP notch, thus eliminating sites of abnormal repolarization and the substrate for ventricular tachycardia ventricular fibrillation.
Project description:The underlying mechanisms of Brugada syndrome (BrS) are not completely understood. Recent studies provided evidence that the electrophysiological substrate, leading to electrocardiogram abnormalities and/or ventricular arrhythmias, is located in the right ventricular outflow tract (RVOT). The purpose of this study was to examine abnormalities of epicardial and endocardial local unipolar electrograms by simultaneous noninvasive mapping in patients with BrS.Local epicardial and endocardial unipolar electrograms were analyzed using a novel noninvasive epi- and endocardial electrophysiology system (NEEES) in 12 patients with BrS and 6 with right bundle branch block for comparison. Fifteen normal subjects composed the control group. Observed depolarization abnormalities included fragmented electrograms in the anatomical area of RVOT endocardially and epicardially, significantly prolonged activation time in the RVOT endocardium (65±20 vs 38±13 ms in controls; P=0.008), prolongation of the activation-recovery interval in the RVOT epicardium (281±34 vs 247±26 ms in controls; P=0.002). Repolarization abnormalities included a larger area of ST-segment elevation >2 mV and T-wave inversions. Negative voltage gradient (-2.5 to -6.0 mV) between epicardium and endocardium of the RVOT was observed in 8 of 12 BrS patients, not present in patients with right bundle branch block or in controls.Abnormalities of epicardial and endocardial electrograms associated with depolarization and repolarization properties were found using NEEES exclusively in the RVOT of BrS patients. These findings support both, depolarization and repolarization abnormalities, being operative at the same time in patients with BrS.
Project description:Background:The early repolarization (ER) pattern is a common ECG finding. Recent studies established a definitive clinical association between ER and fatal ventricular arrhythmias. However, the arrhythmogenic substrate of ER in the intact human heart has not been characterized. Objectives:To map the epicardial electrophysiological (EP) substrate in ER syndrome patients using noninvasive Electrocardiographic Imaging (ECGI), and to characterize substrate properties that support arrhythmogenicity. Methods:Twenty-nine ER syndrome patients were enrolled, 17 of which had a malignant syndrome. Characteristics of the abnormal EP substrate were analyzed using data recorded during sinus rhythm. The EP mapping data were analyzed for electrogram morphology, conduction and repolarization. Seven normal subjects provided control data. Results:The abnormal EP substrate in ER syndrome patients has the following properties: (1) Abnormal epicardial electrograms characterized by presence of J-waves in localized regions; (2) Absence of conduction abnormalities, including delayed activation, conduction block, or fractionated electrograms; (3) Marked abbreviation of ventricular repolarization in areas with J-waves. The action potential duration (APD) was significantly shorter than normal (196±19 vs. 235±21 ms, p<0.05). Shortening of APD occurred heterogeneously, leading to steep repolarization gradients compared to normal control (45±17 vs.7±5 ms/cm, p<0.05). Premature ventricular contractions (PVCs) were recorded in 2 patients. The PVC sites of origin were closely related to the abnormal EP substrate with J-waves and steep repolarization gradients. Conclusions:Early Repolarization is associated with steep repolarization gradients caused by localized shortening of APD. Results suggest association of PVC initiation sites with areas of repolarization abnormalities. Conduction abnormalities were not observed.
Project description:BACKGROUND:Brugada syndrome (BrS) is a highly arrhythmogenic cardiac disorder, associated with an increased incidence of sudden death. Its arrhythmogenic substrate in the intact human heart remains ill-defined. METHODS AND RESULTS:Using noninvasive ECG imaging, we studied 25 BrS patients to characterize the electrophysiological substrate and 6 patients with right bundle-branch block for comparison. Seven healthy subjects provided control data. Abnormal substrate was observed exclusively in the right ventricular outflow tract with the following properties (in comparison with healthy controls; P<0.005): (1) ST-segment elevation and inverted T wave of unipolar electrograms (2.21±0.67 versus 0 mV); (2) delayed right ventricular outflow tract activation (82±18 versus 37±11 ms); (3) low-amplitude (0.47±0.16 versus 3.74±1.60 mV) and fractionated electrograms, suggesting slow discontinuous conduction; (4) prolonged recovery time (381±30 versus 311±34 ms) and activation-recovery intervals (318±32 versus 241±27 ms), indicating delayed repolarization; (5) steep repolarization gradients (?recovery time/?x=96±28 versus 7±6 ms/cm, ?activation-recovery interval/?x=105±24 versus 7±5 ms/cm) at right ventricular outflow tract borders. With increased heart rate in 6 BrS patients, reduced ST-segment elevation and increased fractionation were observed. Unlike BrS, right bundle-branch block had delayed activation in the entire right ventricle, without ST-segment elevation, fractionation, or repolarization abnormalities on electrograms. CONCLUSIONS:The results indicate that both slow discontinuous conduction and steep dispersion of repolarization are present in the right ventricular outflow tract of BrS patients. ECG imaging could differentiate between BrS and right bundle-branch block.
Project description:Early repolarization syndrome (ERS) is associated with polymorphic ventricular tachycardia (PVT) and ventricular fibrillation, leading to sudden cardiac death.The present study tests the hypothesis that the transient outward potassium current (Ito)-blocking effect of phosphodiesterase-3 (PDE-3) inhibitors plays a role in reversing repolarization heterogeneities responsible for arrhythmogenesis in experimental models of ERS.Transmembrane action potentials (APs) were simultaneously recorded from epicardial and endocardial regions of coronary-perfused canine left ventricular (LV) wedge preparations, together with a transmural pseudo-electrocardiogram. The Ito agonist NS5806 (7-15 ?M) and L-type calcium current (ICa) blocker verapamil (2-3 ?M) were used to induce an early repolarization pattern and PVT.After stable induction of arrhythmogenesis, the PDE-3 inhibitors cilostazol and milrinone or isoproterenol were added to the coronary perfusate. All were effective in restoring the AP dome in the LV epicardium, thus abolishing the repolarization defects responsible for phase 2 reentry and PVT. Arrhythmic activity was suppressed in 7 of 8 preparations by cilostazol (10 ?M), 6 of 7 by milrinone (2.5 ?M), and 7 of 8 by isoproterenol (0.1-1 ?M). Using voltage clamp techniques applied to LV epicardial myocytes, both cilostazol (10 ?M) and milrinone (2.5 ?M) were found to reduce Ito by 44.4% and 40.4%, respectively, in addition to their known effects to augment ICa.Our findings suggest that PDE-3 inhibitors exert an ameliorative effect in the setting of ERS by producing an inward shift in the balance of current during the early phases of the epicardial AP via inhibition of Ito as well as augmentation of ICa, thus reversing the repolarization defects underlying the development of phase 2 reentry and ventricular tachycardia/ventricular fibrillation.
Project description:Brugada syndrome (BrS) is one of the most common inherited channelopathies associated with an increased risk of sudden cardiac death. Appropriate use of an ICD in high-risk patients is life-saving. However, there remains a lack of consensus on risk stratification, and even on the diagnosis of BrS itself. Some argue that people with a type 1 Brugada ECG pattern but no symptoms should not be diagnosed with BrS, and guidelines recommend observation without therapy in these patients. Others argue that the presence of a spontaneous (rather than drug-induced) type 1 ECG pattern alone is enough to label them as high-risk for arrhythmic events, particularly if syncope is also present. Syncope and a spontaneous type 1 ECG pattern are the only factors that have consistently been shown to predict ventricular arrhythmic events and sudden cardiac death. Other markers have yielded conflicting data. However, in combination they may have roles in risk scoring models. Epicardial catheter ablation in the right ventricular outflow tract has shown promise in studies as an alternative management option to an ICD, but longer follow-up is required to ensure that the ablation effect is permanent.
Project description:BACKGROUND:Ripple mapping displays every deflection of a bipolar electrogram and enables the visualization of conduction channels (RMCC) within postinfarction ventricular scar to guide ventricular tachycardia (VT) ablation. The utility of RMCC identification for facilitation of VT ablation in the setting of arrhythmogenic right ventricular cardiomyopathy (ARVC) has not been described. OBJECTIVE:We sought to (a) identify the slow conduction channels in the endocardial/epicardial scar by ripple mapping and (b) retrospectively analyze whether the elimination of RMCC is associated with improved VT-free survival, in ARVC patients. METHODS:High-density right ventricular endocardial and epicardial electrograms were collected using the CARTO 3 system in sinus rhythm or ventricular pacing and reviewed for RMCC. Low-voltage zones and abnormal myocardium in the epicardium were identified by using standardized late-gadolinium-enhanced (LGE) magnetic resonance imaging (MRI) signal intensity (SI) z-scores. RESULTS:A cohort of 20 ARVC patients that had undergone simultaneous high-density right ventricular endocardial and epicardial electrogram mapping was identified (age 44?±?13 years). Epicardial scar, defined as bipolar voltage less than 1.0?mV, occupied 47.6% (interquartile range [IQR], 30.9-63.7) of the total epicardial surface area and was larger than endocardial scar, defined as bipolar voltage less than 1.5?mV, which occupied 11.2% (IQR, 4.2?±?17.8) of the endocardium (P?<?0.01). A median 1.5 RMCC, defined as continuous corridors of sequential late activation within scar, were identified per patient (IQR, 1-3), most of which were epicardial. The median ratio of RMCC ablated was 1 (IQR, 0.6-1). During a median follow-up of 44 months (IQR, 11-49), the ratio of RMCC ablated was associated with freedom from recurrent VT (hazard ratio, 0.01; P?=?0.049). Among nine patients with adequate MRI, 73% of RMCC were localized in LGE regions, 24% were adjacent to an area with LGE, and 3% were in regions without LGE. CONCLUSION:Slow conduction channels within endocardial or epicardial ARVC scar were delineated clearly by ripple mapping and corresponded to critical isthmus sites during entrainment. Complete elimination of RMCC was associated with freedom from VT.
Project description:The right ventricular outflow tract (RVOT) is acknowledged to be responsible for arrhythmogenesis in Brugada syndrome (BrS), but the pathophysiology remains controversial.This study assessed the substrate underlying BrS at post-mortem and in vivo, and the role for open thoracotomy ablation.Six whole hearts from male post-mortem cases of unexplained sudden death (mean age 23.2 years) with negative specialist cardiac autopsy and familial BrS were used and matched to 6 homograft control hearts by sex and age (within 3 years) by random risk set sampling. Cardiac autopsy sections from cases and control hearts were stained with picrosirius red for collagen. The RVOT was evaluated in detail, including immunofluorescent stain for connexin-43 (Cx43). Collagen and Cx43 were quantified digitally and compared. An in vivo study was undertaken on 6 consecutive BrS patients (mean age 39.8 years, all men) during epicardial RVOT ablation for arrhythmia via thoracotomy. Abnormal late and fractionated potentials indicative of slowed conduction were identified, and biopsies were taken before ablation.Collagen was increased in BrS autopsy cases compared with control hearts (odds ratio [OR]: 1.42; p = 0.026). Fibrosis was greatest in the RVOT (OR: 1.98; p = 0.003) and the epicardium (OR: 2.00; p = 0.001). The Cx43 signal was reduced in BrS RVOT (OR: 0.59; p = 0.001). Autopsy and in vivo RVOT samples identified epicardial and interstitial fibrosis. This was collocated with abnormal potentials in vivo that, when ablated, abolished the type 1 Brugada electrocardiogram without ventricular arrhythmia over 24.6 ± 9.7 months.BrS is associated with epicardial surface and interstitial fibrosis and reduced gap junction expression in the RVOT. This collocates to abnormal potentials, and their ablation abolishes the BrS phenotype and life-threatening arrhythmias. BrS is also associated with increased collagen throughout the heart. Abnormal myocardial structure and conduction are therefore responsible for BrS.
Project description:Brugada syndrome (BrS) is an inherited cardiac arrhythmia commonly associated with SCN5A mutations, yet its ionic mechanisms remain unclear due to a lack of cellular models. Here, we used human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from a BrS patient (BrS1) to evaluate the roles of Na+ currents (INa) and transient outward K+ currents (Ito) in BrS induced action potential (AP) changes. To understand the role of these current changes in repolarization we employed dynamic clamp to "electronically express" IK1 and restore normal resting membrane potentials and allow normal recovery of the inactivating currents, INa, ICa and Ito. HiPSC-CMs were generated from BrS1 with a compound SCN5A mutation (p. A226V & p. R1629X) and a healthy sibling control (CON1). Genome edited hiPSC-CMs (BrS2) with a milder p. T1620M mutation and a commercial control (CON2) were also studied. CON1, CON2 and BrS2, had unaltered peak INa amplitudes, and normal APs whereas BrS1, with over 75% loss of INa, displayed a loss-of-INa basal AP morphology (at 1.0?Hz) manifested by a reduced maximum upstroke velocity (by ~80%, p?<?0.001) and AP amplitude (p?<?0.001), and an increased phase-1 repolarization pro-arrhythmic AP morphology (at 0.1?Hz) in ~25% of cells characterized by marked APD shortening (~65% shortening, p?<?0.001). Moreover, Ito densities of BrS1 and CON1 were comparable and increased from 1.0?Hz to 0.1?Hz by ~ 100%. These data indicate that a repolarization deficit could be a mechanism underlying BrS.
Project description:The experiments investigated the applicability of two established criteria for arrhythmogenicity in Scn5a+/Delta and Scn5a+/- murine hearts modelling the congenital long QT syndrome type 3 (LQT3) and the Brugada syndrome (BrS). Monophasic action potentials (APs) recorded during extrasystolic stimulation procedures from Langendorff-perfused control hearts and hearts treated with flecainide (1 microM) or quinidine (1 or 10 microM) demonstrated that both agents were pro-arrhythmic in wild-type (WT) hearts, quinidine was pro-arrhythmic in Scn5a+/Delta hearts, and that flecainide was pro-arrhythmic whereas quinidine was anti-arrhythmic in Scn5a+/- hearts, confirming clinical findings. Statistical analysis confirmed a quadratic relationship between epicardial and endocardial AP durations (APDs) in WT control hearts. However, comparisons between plots of epicardial against endocardial APDs and this reference curve failed to correlate with arrhythmogenicity. Restitution curves, relating APD to diastolic interval (DI), were then constructed for the first time in a murine system and mono-exponential growth functions fitted to these curves. Significant (P<0.05) alterations in the DI at which slopes equalled unity, an established indicator of arrhythmogenicity, now successfully predicted the presence or absence of arrhythmogenicity in all cases. We thus associate changes in the slopes of restitution curves with arrhythmogenicity in models of LQT3 and BrS.
Project description:AIMS:Treatment of arrhythmias evoked by hypothermia/rewarming remains challenging, and the underlying mechanisms are unclear. This in vitro experimental study assessed cardiac electrophysiology in isolated rabbit hearts at temperatures occurring in therapeutic and accidental hypothermia. METHODS AND RESULTS:Detailed ECG, surface electrogram, and panoramic optical mapping were performed in isolated rabbit hearts cooled to moderate (31°C) and severe (17°C) hypothermia. Ventricular activation was unchanged at 31°C while action potential duration (APD) was significantly prolonged (176.9?±?4.2?ms vs. 241.0?±?2.9?ms, P?<?0.05), as was ventricular repolarization. At 17°C, there were proportionally similar delays in both activation and repolarization. These changes were reflected in the QRS and QT intervals of ECG recordings. Ventricular fibrillation threshold was significantly reduced at 31°C (16.3?±?3.1 vs. 35?±?3.5?mA, P?<?0.05) but increased at 17°C (64.2?±?9.9, P?<?0.05). At 31°C, transverse conduction was relatively unchanged by cooling compared to longitudinal conduction, but at 17°C both transverse and longitudinal conduction were proportionately reduced to a similar extent. The gap junction uncoupler heptanol had a larger relative effect on transverse than longitudinal conduction and was able to restore the transverse/longitudinal conduction ratio, returning ventricular fibrillation threshold to baseline values (16.3?±?3.1 vs. 36.3?±?4.3?mA, P?<?0.05) at 31°C. Rewarming to 37°C restored the majority of the electrophysiological parameters. CONCLUSIONS:Moderate hypothermia does not significantly change ventricular conduction time but prolongs repolarization and is pro-arrhythmic. Further cooling to severe hypothermia causes parallel changes in ventricular activation and repolarization, changes which are anti-arrhythmic. Therefore, relative changes in QRS and QT intervals (QR/QTc) emerge as an ECG-biomarker of pro-arrhythmic activity. Risk for ventricular fibrillation appears to be linked to the relatively low temperature sensitivity of ventricular transmural conduction, a conclusion supported by the anti-arrhythmic effect of heptanol at 31°C.