Mode of onset of ventricular fibrillation in patients with Brugada syndrome detected by implantable cardioverter defibrillator therapy

Origin of ventricular fibrillation triggers in a model of localized repolarization heterogeneity

BACKGROUND

Heterogeneities in ventricular repolarization contribute significantly to the genesis of ventricular fibrillation (VF). Although clinical arrhythmias are spontaneously triggered by premature ventricular complexes, these triggers are difficult to document and little is known about their site of origin.

OBJECTIVES

The purpose of this study was to characterize spontaneous VF initiation in an experimental model of repolarization heterogeneity and to identify the origin of triggers in relation to the spatial dispersion of repolarization.

METHODS

Spatially limited repolarization heterogeneity was created in isolated perfused porcine right ventricles (N = 16) by local administration of pinacidil (20 μM) in a terminal branch of the right coronary artery. High-resolution optical mapping and pseudo-electrocardiography were performed under control conditions and after pinacidil perfusion.

RESULTS

No arrhythmia occurred at baseline, but 74 VF episodes were observed in 13 hearts (82%) after pinacidil perfusion and were most often initiated by a ventricular trigger with a short coupling interval (297 ± 66 ms). Sixteen VF initiations were optically mapped in 4 hearts. Mapping showed triggers originating in all cases from the border zone between altered and normal repolarization areas where local action potential duration and repolarization time gradients were steep (15.9 and 15.8 ms/mm vs 1.5 and 3.0 ms/mm at nontrigger sites). Optical action potential traces were compatible with a phase 2 reexcitation mechanism. The subsequent VF cycles were driven by activities located in the same region.

CONCLUSION

This model of localized repolarization heterogeneity is able to produce spontaneous VF initiation. Our study demonstrates that VF triggers originate consistently from the border zone of repolarization dispersion.

Outcomes of catheter ablation in high-risk patients with Brugada syndrome refusing an implantable cardioverter defibrillator implantation

AIMS

The aim of this study was to investigate the outcomes of catheter ablation (CA) in preventing arrhythmic events among patients with symptomatic Brugada syndrome (BrS) who declined implantable cardioverter defibrillator (ICD) implantation.

METHODS AND RESULTS

A total of 40 patients with symptomatic BrS were included in the study, of which 18 refused ICD implantation and underwent CA, while 22 patients received ICD implantation. The study employed substrate modification (including endocardial and epicardial approaches) and ventricular fibrillation (VF)-triggering pre-mature ventricular contraction (PVC) ablation strategies. The primary outcomes were a composite endpoint consisting of episodes of VF and sudden cardiac death during the follow-up period. The study population had a mean age of 43.8 ± 9.6 years, with 36 (90.0%) of them being male. All patients exhibited the typical Type 1 BrS electrocardiogram pattern, and 16 (40.0%) were carriers of an SCN5A mutation. The Shanghai risk scores were comparable between the CA and the ICD groups (7.05 ± 0.80 vs. 6.71 ± 0.86, P = 0.351). Ventricular fibrillation-triggering PVCs were ablated in 3 patients (16.7%), while VF substrates were ablated in 15 patients (83.3%). Epicardial ablation was performed in 12 patients (66.7%). During a median follow-up of 46.2 (17.5-73.7) months, the primary outcomes occurred more frequently in the ICD group than in the CA group (5.6 vs. 54.5%, Log-rank P = 0.012).

CONCLUSION

Catheter ablation is an effective alternative therapy for improving arrhythmic outcomes in patients with symptomatic BrS who decline ICD implantation. Our findings support the consideration of CA as an alternative treatment option in this population.

Efficacy and safety of catheter ablation for Brugada syndrome: an updated systematic review

BACKGROUND

Patients with Brugada syndrome (BrS) may experience recurrent ventricular arrhythmias (VAs). Catheter ablation is becoming an emerging paradigm for treatment of BrS.

OBJECTIVE

To assess the efficacy and safety of catheter ablation in BrS in an updated systematic review.

METHODS

We comprehensively searched the databases of Pubmed/Medline, EMBASE, and Cochrane Central Register of Controlled Trials from inception to 11th of August 2021.

RESULTS

Fifty-six studies involving 388 patients were included. A substrate-based strategy was used in 338 cases (87%), and a strategy of targeting premature ventricular complex (PVCs)/ventricular tachycardias (VTs) that triggered ventricular fibrillation (VF) in 47 cases (12%), with combined abnormal electrogram and PVC/VT ablation in 3 cases (1%). Sodium channel blocker was frequently used to augment the arrhythmogenic substrate in 309/388 cases (80%), which included a variety of agents, of which ajmaline was most commonly used. After ablation procedure, the pooled incidence of non-inducibility of VA was 87.1% (95% confidence interval [CI], 73.4-94.3; I2 = 51%), and acute resolution of type I ECG was seen in 74.5% (95% CI [52.3-88.6]; I2 = 75%). Over a weighted mean follow up of 28 months, 7.6% (95% CI [2.1-24]; I2 = 67%) had recurrence of type I ECG either spontaneously or with drug challenge and 17.6% (95% CI [10.2-28.6]; I2 = 60%) had recurrence of VA.

CONCLUSION

Catheter ablation appears to be an efficacious strategy for elimination of arrhythmias or substrate associated with BrS. Further study is needed to identify which patients stand to benefit, and optimal provocation protocol for identifying ablation targets.

Investigation of Unexplained Cardiac Arrest: Phenotyping and Genetic Testing

Unexplained cardiac arrest (UCA) is a working diagnosis that should be replaced by a final diagnosis once evaluation is completed. Complete evaluation of UCA should include high-yield tests like cardiac magnetic resonance imaging, exercise treadmill test, and sodium-channel blocker challenge to identify latent causes of UCA. If no clear etiology is revealed after complete evaluation, idiopathic ventricular fibrillation may be diagnosed, and the strength of its diagnosis can be divided into definitive, probable, and possible based on the number of high-yield tests performed. Care should be provided by a multidisciplinary team with expertise in this area.

R-on-T and the initiation of reentry revisited: Integrating old and new concepts

Initiation of reentry requires 2 factors: (1) a triggering event, most commonly focal excitations such as premature ventricular complexes (PVCs); and (2) a vulnerable substrate with regional dispersion of refractoriness and/or excitability, such as occurs during the T wave of the electrocardiogram when some areas of the ventricle have repolarized and recovered excitability but others have not. When the R wave of a PVC coincides in time with the T wave of the previous beat, this timing can lead to unidirectional block and initiation of reentry, known as the R-on-T phenomenon. Classically, the PVC triggering reentry has been viewed as arising focally from 1 region and propagating into another region whose recovery is delayed, resulting in unidirectional conduction block and reentry initiation. However, more recent evidence indicates that PVCs also can arise from the T wave itself. In the latter case, the PVC initiating reentry is not a separate event from the T wave but rather is causally generated from the repolarization gradient that manifests as the T wave. We call the former an "R-to-T" mechanism and the latter an "R-from-T" mechanism, which are initiation mechanisms distinct from each other. Both are important components of the R-on-T phenomenon and need to be taken into account when designing antiarrhythmic strategies. Strategies targeting suppression of triggers alone or vulnerable substrate alone may be appropriate in some instances but not in others. Preventing R-from-T arrhythmias requires suppressing the underlying dynamic tissue instabilities responsible for producing both triggers and substrate vulnerability simultaneously. The same principles are likely to apply to supraventricular arrhythmias.

Significance of Exercise-Related Ventricular Arrhythmias in Patients With Brugada Syndrome

Background

Sinus tachycardia during exercise attenuates ST‐segment elevation in patients with Brugada syndrome, whereas ST‐segment augmentation after an exercise test is a high‐risk sign. Some patients have premature ventricular contractions (PVCs) related to exercise, but the significance of exercise‐related PVCs in patients with Brugada syndrome is still unknown. The objective of this study was to determine the significance of exercise‐related PVCs for predicting occurrence of ventricular fibrillation (VF) in patients with Brugada syndrome.

Methods and Results

The subjects were 307 patients with Brugada syndrome who performed a treadmill exercise test. We evaluated the occurrence of PVCs at rest, during exercise and at the peak of exercise, and during recovery after exercise (0–5 minutes). We followed the patients for 92±68 months and evaluated the occurrence of VF. PVCs occurred in 82 patients (27%) at the time of treadmill exercise test: PVCs appeared at rest in 14 patients (4%), during exercise in 60 patients (20%), immediately after exercise (0–1.5 minutes) in 28 patients (9%), early after exercise (1.5–3 minutes) in 18 patients (6%), and late after exercise (3–5 minutes) in 12 patients (4%). Thirty patients experienced VF during follow‐up. Multivariable analysis including symptoms, spontaneous type 1 ECG, and PVCs in the early recovery phase showed that these factors were independently associated with VF events during follow‐up.

Conclusions

PVCs early after an exercise test are associated with future occurrence of VF events. Rebound of vagal nerve activity at the early recovery phase would promote ST‐segment augmentation and PVCs in high‐risk patients with Brugada syndrome.

Mechanism of spontaneous initiation of ventricular fibrillation in patients with implantable defibrillators

INTRODUCTION

To improve the mechanistic understanding of spontaneous initiation of ventricular fibrillation (VF), we characterized the patterns of premature ventricular complex (PVC) preceding spontaneous VF in primary and secondary implantable cardioverter-defibrillator (ICD) recipients.

METHODS AND RESULTS

A single-center, cross-sectional analysis of 1209 patients with primary and secondary prevention ICD identified 190 patients who received ICD therapy (firing or antitachycardia pacing) for VF or monomorphic ventricular tachycardia (MMVT). Initiation was quantified by the coupling interval (CI), the cycle length immediately preceding the CI (CL(-1)), the CI corrected by CL(-1) using Fridericia's formula (CIc), and the prematurity index (PI). In both VF (n = 44; 23%) and MMVT (n = 134; 71%), the most common pattern of initiation was late-coupled PVC, followed by the short-long-short pattern. The parameters such as pre-initiation median CL, CL(-1), CI, and PI were not significantly different between VF and MMVT for any patterns. At least some events (45% of VF and 63% of MMVT) had extremely long CIs beyond the QTc cut-off estimated from the CL(-1), suggestive of initiation by a train of multiple PVCs or nonsustained VT instead of a single PVC.

CONCLUSION

Some spontaneous VF events in ICD recipients appear to be initiated by a train of multiple PVC or nonsustained VT rather than a single PVC. This finding indicates that patterns of a single PVC are not an important determinant of VF initiation and thus account for conflicting results in previous studies.

A case of a late fatal complication after atrial fibrillation ablation related to a prolonged QT interval unmasked by atrial fibrillation ablation

A 79-year-old woman with a history of atrial fibrillation (AF) ablation was referred to our hospital for ventricular fibrillation, which was terminated by an automated external defibrillator. The heart rate corrected QT interval was 489 ms. The electrocardiogram monitoring recorded a polymorphic ventricular tachycardia (VT) reproducibly induced by a single morphology premature ventricular contraction (PVC). Therefore, we performed a trigger PVC ablation and implanted an implantable cardioverter defibrillator. No VT events were observed for at least one year after the ablation. A prolonged QT interval after the AF ablation should be carefully noted because it could introduce fatal complications. <Learning objective: A rare late fatal complication of ventricular tachycardia (VT) after atrial fibrillation (AF) ablation can occur even more than one month after the AF ablation. The AF ablation might have an adverse effect on the masked prolonged QT interval. A trigger ablation of the polymorphic VT was helpful to control lethal VTs.>.

Electrocardiographic imaging of the arrhythmogenic substrate of Brugada syndrome: Current evidence and future perspectives

Brugada syndrome is responsible for about 20% of sudden cardiac deaths in patients with apparently normal hearts. Basic and clinical research has elucidated some of the mechanisms that are responsible for life-threatening ventricular arrhythmias in this syndrome. Delays in activation and repolarization over the right ventricular outflow tract are the most likely cause of the ECG typical pattern and arrhythmogenesis. Invasive epicardial and endocardial mapping has identified the epicardium as the principal region of interest for these anomalies, and areas of fragmented potentials at invasive mapping are a target for epicardial ablation. Noninvasive mapping systems have been developed to study the epicardial depolarization and repolarization and may be particularly useful in assessing the epicardial arrhythmogenic substrate of Brugada syndrome for both clinical and research purpose. This review focuses on recent advances in this field.

Catheter Ablation for Brugada Syndrome

Brugada syndrome (BrS) is an arrhythmogenic disease associated with an increased risk of ventricular fibrillation (VF) and sudden cardiac death (SCD). To date, the standard therapy for the prevention of SCD in BrS is the use of an implantable cardioverter-defibrillator (ICD) especially in patients who have experienced a prior cardiac arrest or syncopal events secondary to VF. However, ICDs do not prevent the occurrence of VF but react to defibrillate the VF episode, thereby preventing SCD. Often patients with recurrent VF have to be maintained on antiarrhythmic drugs that are effective but have remarkable adverse effects. An alternative therapy for BrS with recurrent VF is catheter ablation which emerged as an effective therapy in eliminating VF-triggering premature ventricular complexes in limited case series; however, there has been a remarkable progress in effectiveness of catheter ablation since epicardial substrate ablation was first applied in 2011 and such approach is now widely applicable.

Catheter ablation for electrical storm in Brugada syndrome: Results of substrate based ablation

Background

Brugada syndrome (BrS) is known to cause malignant ventricular arrhythmia (VA) and sudden cardiac death (SCD). Patients with implantable cardioverter defibrillator (ICD) may experience recurrent shocks from ICD. Recent reports indicate that radiofrequency ablation (RFA) in BrS is feasible, and effective. Catheter ablation of premature ventricular complexes (PVCs) triggering VA and substrate modification of right ventricular outflow tract (RVOT) has been described.

Methods and results

Five patients (4 males, age-23 to 32 years) with BrS and electrical storm (ES) despite being on isoprenaline infusion and cilostazol (phosphodiestrase-3 inhibitor) underwent 3 dimensional electroanatomic mapping and RFA. Ventricular fibrillation was easily inducible in two patients. Voltage map of right ventricle was created in sinus rhythm in all patients. Substrate modification of RVOT was performed endocardially in one patient, both endocardial and epicardial in three and only epicardially in one patient. Brugada pattern gradually resolved over one week in all patients post procedure. These patients completed follow up of median 40 months (1.5–70). One patient had inappropriate shock due to atrial fibrillation, one had an episode of VF and appropriate shock 24 months after the RFA. The remaining four patients had no device therapy or VA in device log on follow up.

Conclusion

Abnormal myocardial substrate is observed in RVOT among patients with BrS. Substrate modification in these patients may abolish Brugada pattern on the ECG and prevents spontaneous VAs on long term follow up.

SCN5A mutation type and topology are associated with the risk of ventricular arrhythmia by sodium channel blockers

BACKGROUND

Ventricular fibrillation in patients with Brugada syndrome (BrS) is often initiated by premature ventricular contractions (PVCs). Presence of SCN5A mutation increases the risk of PVCs upon exposure to sodium channel blockers (SCB) in patients with baseline type-1 ECG. In patients without baseline type-1 ECG, however, the effect of SCN5A mutation on the risk of SCB-induced arrhythmia is unknown. We aimed to establish whether presence/absence, type, and topology of SCN5A mutation correlates with PVC occurrence during ajmaline infusion.

METHODS AND RESULTS

We investigated 416 patients without baseline type-1 ECG who underwent ajmaline testing and SCN5A mutation analysis. A SCN5A mutation was identified in 88 patients (S⁺). Ajmaline-induced PVCs occurred more often in patients with non-missense mutations (S^non-missense) or missense mutations in transmembrane or pore regions of SCN5A-encoded channel protein (S^missense-TP) than patients with missense mutations in intra-/extracellular channel regions (S^missense-IE) and patients without SCN5A mutation (S^-) (29%, 24%, 9%, and 3%, respectively; P<0.001). The proportion of patients with ajmaline-induced BrS was similar in different mutation groups but lower in S^- (71% S^non-missense, 63% S^missense-TP, 70% S^missense-IE, and 34% S^-; P<0.001). Logistic regression indicated S^non-missense and S^missense-TP as predictors of ajmaline-induced PVCs.

CONCLUSIONS

SCN5A mutation is associated with an increased risk of drug-induced ventricular arrhythmia in patients without baseline type-1 ECG. In particular, S^non-missense and S^missense-TP are at high risk.

Brugada Syndrome: An Intriguing Phenomenon

Brugada Syndrome has a unique electrocardiographic pattern of downsloping ST-segment elevation in the right praecordial leads (V1 to V3), right bundle branch block pattern and a normal QT-interval. Intermittent and concealed forms do exist. It is important for emergency physicians to recognise this ECG marker of sudden cardiac death. We report the case of a young man who presented to the Emergency Department with chest pain, and whose ECG was diagnostic of Brugada Syndrome. This is followed by a discussion on its recognition, postulated mechanisms and current mode of management.

Electrical Substrate Elimination in 135 Consecutive Patients With Brugada Syndrome

BACKGROUND

There is emerging evidence that localization and elimination of abnormal electric activity in the epicardial right ventricular outflow tract may be beneficial in patients with Brugada syndrome.

METHODS AND RESULTS

A total of 135 symptomatic Brugada syndrome patients having implantable cardiac defibrillator were enrolled: 63 (group 1) having documented ventricular tachycardia (VT)/ventricular fibrillation (VF) and Brugada syndrome-related symptoms, and 72 (group 2) having inducible VT/VF without ECG documentation at the time of symptoms. About 27 patients of group 1 experienced multiple implantable cardiac defibrillator shocks for recurrent VT/VF episodes. Three-dimensional maps before and after ajmaline determined the arrhythmogenic electrophysiological substrate (AES) as characterized by prolonged fragmented ventricular potentials. Primary end point was identification and elimination of AES leading to ECG pattern normalization and VT/VF noninducibility. Extensive areas of AES were found in the right ventricle epicardium, which were wider in group 1 (P=0.007). AES increased after ajmaline in both groups (P<0.001) and was larger in men (P=0.008). The increase of type-1 ST-segment elevation correlated with AES expansion (r=0.682, P<0.001). Radiofrequency ablation eliminated AES leading to ECG normalization and VT/VF noninducibility in all patients. During a median follow-up of 10 months, the ECG remained normal even after ajmaline in all except 2 patients who underwent a repeated effective procedure for recurrent VF.

CONCLUSIONS

In Brugada syndrome, AES is commonly located in the right ventricle epicardium and ajmaline exposes its extent and distribution, which is correlated with the degree of coved ST-elevation. AES elimination by radiofrequency ablation results in ECG normalization and VT/VF noninducibility. Substrate-based ablation is effective in potentially eliminating the arrhythmic consequences of this genetic disease.

CLINICAL TRIAL REGISTRATION

URL: https://clinicaltrials.gov. Unique identifier: NCT02641431.

Distribution and Prognostic Significance of Fragmented QRS in Patients With Brugada Syndrome

Background—

Fragmented QRS complexes (fQRS) in the right precordial leads are associated with occurrence of ventricular fibrillation (VF) in Brugada syndrome. Recently, epicardial mapping has revealed abnormal electrograms at the right ventricular (RV) outflow tract and inferior region of the right ventricle. fQRS may reflect the extent of the area of abnormal potentials, but whether the distribution of fQRS has prognostic value is not known.

Methods and Results—

We evaluated the existence of fQRS in 456 patients with Brugada syndrome, including 117 patients with syncope and 23 patients with VF. The region of fQRS was defined as inferior (II, III, and aVF), lateral (I, aVL, and V5 and V6), anterior (V3 and V4), RV (V1 and V2), and RV outflow tract (V1 and V2 at the third intercostal space). fQRS were present in 229 patients (RV outflow tract in 175, inferior in 135, RV in 90, and lateral in 16 patients). During follow-up (mean 91 months), 39 patients experienced VF. In univariable analyses, fQRS in any distribution and fQRS in each region excluding the RV were associated with VF. Multivariable analysis showed that fQRS in the inferior (hazard ratio, 3.9; confidence interval, 1.9–8.5), lateral (hazard ratio, 3.5; confidence interval, 1.2–8.2), and RV outflow tract (hazard ratio, 2.5; confidence interval, 1.2–5.6) were associated with VF events. The presence of multiple regions of fQRS was associated with worse prognosis.

Conclusions—

The distribution of fQRS is associated with prognosis in Brugada syndrome, further supporting the association of fQRS and arrhythmia substrate.

A novel method to enhance phenotype, epicardial functional substrates, and ventricular tachyarrhythmias in Brugada syndrome

BACKGROUND

Fever is associated with the manifestation of Brugada phenotype and ventricular tachycardia/ventricular fibrillation (VT/VF) in patients with Brugada syndrome (BrS). The thermal effect on the pathogenesis of functional substrates in BrS remains unknown.

OBJECTIVE

This study aimed to elucidate the thermal effect on BrS phenotype, VT/VF, and electrophysiological characteristics of epicardial functional substrates in BrS.

METHODS

We consecutively studied 15 patients with BrS receiving radiofrequency catheter ablation for drug-refractory ventricular tachyarrhythmias. Baseline characteristics, electrocardiographic features, and changes in epicardial functional substrates before and after epicardial warm water instillation (n = 6) were recorded and analyzed.

RESULTS

A total of 15 male patients (mean age 41.3 ± 10.3 years) with type 1 BrS presenting with ventricular tachyarrhythmias were consecutively enrolled. Epicardial mapping in 11 patients demonstrated a significantly larger epicardial scar/low-voltage zone (LVZ) area within the right ventricular outflow tract and anterior right ventricular free wall than within the endocardium (6.32 ± 12.74 cm² vs 52.91 ± 45.25 cm²; P = .007). Epicardial warm water instillation in 6 patients led to a significant enlargement of the functional scar/LVZ area (123.83 ± 35.26 cm² vs 63.53 ± 40.57 cm²; P = .03), accelerated conduction velocity of the endocardium and epicardium without scar/LVZ area, and increased VT/VF inducibility (16.7% vs 100%; P = .02). Ablation by targeting premature ventricular complexes and/or epicardial abnormal substrates rendered noninducibility of VT/VF and prevented the recurrences of VT/VF.

CONCLUSION

Epicardial warm water instillation enhanced functional epicardial substrates, which contributed to the increased inducibility of ventricular tachyarrhythmias in BrS. Ablation by targeting the triggers and abnormal epicardial substrates provided an effective strategy for preventing ventricular tachyarrhythmia recurrences in BrS.

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Zusammenfassung. Das Brugada-Syndrom ist ein seltenes, meist familiäres Arrhythmie-Syndrom mit autosomal-dominantem Vererbungsmuster und stellt eine wichtige Differenzialdiagnose von rhythmogenen Synkopen bzw. überlebtem plötzlichen Herztod bei jungen Erwachsenen ohne strukturelle Herzerkrankung dar. Die Diagnostik ist meist erschwert, da die pathognomonischen EKG-Zeichen häufig transient sind und zur definitiven Diagnose oft eine medikamentöse Demaskierung mittels Natriumblocker nötig ist. Die ICD-Implantation ist die einzige effektive Therapie zur Prävention des plötzlichen Herztodes. Für die diesbezügliche Therapieentscheidung ist vor allem bei Zufallsbefunden und asymptomatischen Patienten eine individuelle Risikostratifizierung nötig.

Ion Channel Diseases: an Update for 2016

OPINION STATEMENT

Ion channelopathies are a frequent cause of sudden cardiac death (SCD) in patients with structurally normal hearts. These are generally Mendelian inherited electrical disorders with variable penetrance and expressivity. The ability to predict the development of life threatening arrhythmias in these patients is challenging. This chapter will present an update on the genetics, the role of genetic testing, and management of the inherited cardiac channelopathies with a focus on the relatively more common syndromes associated with an increased risk of SCD.

Radiofrequency Ablation to Prevent Sudden Cardiac Death

Radiofrequency ablation may prevent or treat atrial and ventricular arrhythmias. Since some of these arrhythmias are associated with sudden cardiac death, it has been hypothesized that ablation may prevent sudden death in certain cases. We performed a literature search to better understand under which circumstances ablation may prevent sudden death and found little randomized data demonstrating the long-term effects of ablation. Current literature shows that ablation clearly prevents symptoms of arrhythmia and may reduce the incidence of sudden cardiac death in select patients, although data does not indicate improved mortality. Ongoing clinical trials are needed to better define the role of ablation in preventing sudden cardiac death.

[Brugada ECG]

The Brugada syndrome (BrS) is characterized by a typical electrocardiogram (ECG) pattern of right precordial ST-segment elevation and the cardinal symptoms syncope and sudden cardiac death as clinical correlate of malignant ventricular arrhythmias in young adults without structural heart disease. The diagnosis of a type 1 Brugada-ECG is based on the documentation of a coved-type (≥ 0.2 mV) ST elevation followed by a negative T wave. The use of the ECG criteria postulated in the consensus of 2012 is helpful to distinguish between saddleback-type 2 (or type 3) J point/ST elevation and incomplete right bundle branch block. Spontaneous or drug-induced type 1 ST elevation can frequently only be detected in a single right precordial lead (V1 or V2), occurs sometimes together with a type 2 (or type 3) pattern in one and the same 12-lead ECG and can sometimes only be seen in modified right precordial leads. The ST elevation is less pronounced in females. Spontaneous and exercise-induced type 1 ST elevation, fragmented QRS complex, prolonged PR interval (> 200 ms), QRS prolongation in V2 (≥ 120 ms) and markers of an increased heterogeneity of ventricular repolarization are associated with an increased arrhythmic risk. The occurrence of spontaneous or dynamic type 1 ST elevation, a macroscopic T wave alternans or pronounced inferior (lateral) J point/ST elevation are signs of acute electrical instability.

Genetically engineered SCN5A mutant pig hearts exhibit conduction defects and arrhythmias

SCN5A encodes the α subunit of the major cardiac sodium channel Na(V)1.5. Mutations in SCN5A are associated with conduction disease and ventricular fibrillation (VF); however, the mechanisms that link loss of sodium channel function to arrhythmic instability remain unresolved. Here, we generated a large-animal model of a human cardiac sodium channelopathy in pigs, which have cardiac structure and function similar to humans, to better define the arrhythmic substrate. We introduced a nonsense mutation originally identified in a child with Brugada syndrome into the orthologous position (E558X) in the pig SCN5A gene. SCN5A(E558X/+) pigs exhibited conduction abnormalities in the absence of cardiac structural defects. Sudden cardiac death was not observed in young pigs; however, Langendorff-perfused SCN5A(E558X/+) hearts had an increased propensity for pacing-induced or spontaneous VF initiated by short-coupled ventricular premature beats. Optical mapping during VF showed that activity often began as an organized focal source or broad wavefront on the right ventricular (RV) free wall. Together, the results from this study demonstrate that the SCN5A(E558X/+) pig model accurately phenocopies many aspects of human cardiac sodium channelopathy, including conduction slowing and increased susceptibility to ventricular arrhythmias.

Remote monitoring of a high-risk patient with Brugada syndrome: association of different arrhythmic manifestations

We report on the remote arrhythmia monitoring of a 34-year-old man with highly symptomatic Brugada syndrome, who initially presented with syncope, paroxysmal atrial fibrillation, and spontaneous coved-type electrocardiogram. The patient received a dual-chamber implantable cardioverter-defibrillator (ICD) with Home Monitoring™ facilities and experienced recurrent ICD shocks for spontaneous ventricular fibrillation (VF) episodes during the first year after ICD implantation. Remote monitoring revealed an increased burden of premature ventricular complexes and atrial arrhythmias each time VF spontaneously occurred. Atrial and ventricular arrhythmias were effectively suppressed by low-dose quinidine without severe side effects.

Brugada Syndrome 2010

The Brugada syndrome is a genetically determined cardiac disorder, presenting with characteristic electrocardiogram features and high risk of sudden cardiac death from polymorphic ventricular tachycardia/ventricular fibrillation in young individuals with a structurally normal heart. Scientific knowledge about the disease has grown exponentially in recent years. Two consensus reports on the disease were published (in 2002 and 2005) in an effort to state diagnostic criteria, risk stratification, and treatment indications. However, substantial controversies remain, especially considering risk stratification of asymptomatic patients. Given the enormous amount of valuable information collected by many groups since the consensus reports, current diagnostic criteria, recommended prognostic tools, and treatment must be reviewed. This article briefly reviews recent advances in understanding of Brugada syndrome and its genetic and molecular basis, arrhythmogenic mechanisms, and clinical course. An update of tools for risk stratification and treatment of the condition is also included.

Premature ventricular complexes as a trigger for ventricular fibrillation

INTRODUCTION AND OBJECTIVES

The mechanisms that trigger ventricular fibrillation (VF) are poorly understood. The aim of this study was to analyze the initiation of VF in electrograms stored in implantable cardioverter-defibrillators (ICDs).

METHODS

We analyzed ICD electrograms from patients who had suffered at least one episode of VF.

RESULTS

Of 250 patients with ICDs, 13 (10 male and 3 female, age 49+/-22 years) had at least one episode of VF. The diagnoses were Brugada syndrome (n=4), ischemic heart disease (n=3), dilated cardiomyopathy (n=2), hypertrophic cardiomyopathy (n=1), short-coupled variant of torsades de pointes (n=1), endocardial fibroelastosis (n=1) and idiopathic VF (n=1). In 7 patients, VF was the reason for ICD implantation. Overall, 31 episodes of VF were recorded, including three episodes of arrhythmic storm. In the 7 patients who had more than one episode of VF (within minutes or up to 3 years apart), all episodes started with premature ventricular complexes (PVCs) that had the same morphology and similar coupling intervals. A short-long-short cycle was observed in 2 patients. In 21 episodes, PVCs that did not trigger VF were observed during sinus rhythm. There was no significant difference between them and PVCs that did trigger VF in terms of morphology, coupling interval (409+/-121 ms vs. 411+/-123 ms) or the preceding sinus rhythm RR interval (801+/-233 ms vs. 793+/-230 ms).

CONCLUSIONS

Spontaneous VF in the form of an arrhythmic storm or an isolated episode were triggered by PVCs. On occasions, PVCs preceded VF without triggering it.

A phenotypic combination of idiopathic VF and Brugada syndrome

This case study shows a young male presenting a mixture of two disease entities: (1) Brugada syndrome with a nearly-normal baseline electrocardiogram and positive Ajmaline drug challenge as well as (2) idiopathic ventricular fibrillation including extremely short-coupled monomorphic ventricular premature beats (VPB) triggering ventricular fibrillation (coupling interval 318 ± 21 ms). In this phenotypic patient group-more suggestive of idiopathic ventricular fibrillation due to the ultra-short coupling interval of the VPBs-drug treatment with a class IA agent such as Quinidine might be an important option to implantable cardioverter-defibrillator and ablation therapy.

Number of electrocardiogram leads displaying the diagnostic coved-type pattern in Brugada syndrome: a diagnostic consensus criterion to be revised

AIMS

According to the diagnostic consensus criteria, the electrocardiographic (ECG) diagnosis of Brugada syndrome requires coved-type > or =2 mm ST-segment elevation in >1 right precordial lead (RPL) V1-V3 in the presence or absence of a sodium-channel blocker. However, this consensus has not been evaluated. We aimed to assess the distribution of coved-type ST-segment elevation on RPLs in a large patient cohort to reevaluate the appropriateness of the diagnostic consensus criteria.

METHODS AND RESULTS

We included 186 individuals with spontaneous and/or drug-induced ECGs of coved-type > or =2 mm ST-segment elevation in at least one RPL. A total of 376 ECGs were analysed for the number, distribution and maximal J-point elevation of diagnostic RPLs. Among all ECGs, 27 (7%) showed a coved-type pattern in 3 RPLs, 205 (55%) in 2 RPLs, and 144 (38%) in only 1 RPL. Leads V1 and V2 were diagnostic in 99% of all ECGs with two diagnostic RPLs. Lead V3 alone was not diagnostic in any ECG. Maximal J-point elevation was significantly higher in lead V2 than V1. Sixty case subjects (32%) had only ECGs with one RPL displaying a coved-type ST-segment elevation. There was no significant difference in clinical presentation and outcome compared with the 126 Brugada patients with ECGs displaying >1 diagnostic RPL. Major arrhythmic events occurred with the same rate (8%) in both groups during a follow-up >5 years.

CONCLUSION

Lead V3 does not yield diagnostic information in Brugada syndrome. Individuals with ECGs displaying only one diagnostic RPL have a similar clinical profile and arrhythmic risk as Brugada patients with ECGs displaying >1 diagnostic RPL. Revision of the consensus criteria should be considered.

Same morphology of ventricular premature complexes triggering repeated ventricular fibrillation

BACKGROUND

Episodes ventricular fibrillation (VF) initiated by ventricular premature complexes (VPCs) of a single morphology have been reported. However, the characteristics of the VPCs over long periods of time are unknown.

OBJECTIVES

To compare the morphologies and coupling intervals of VPCs that initiate episodes of VF that occur at different time periods.

METHODS

The database of the follow-up of the International Classification of Diseases (ICD) unit was reviewed and patients having at least two spontaneous VF episodes with available recorded EGMs in unipolar and bipolar configuration were included in the study. The coupling interval and morphology of the initiating beat were analyzed.

RESULTS

Nine out of 300 patients with ICD had two or more spontaneous VF episodes. The time interval between episodes ranged from seconds (arrhythmic storm) to 3 years. The fibrillatory VPCs presented the same morphology in both recordings in all episodes of each patient. The coupling intervals of VPCs initiating VF were close for the episodes that occurred during a single arrhythmic storm and were more variable when the time intervals between episodes of VF were longer.

CONCLUSION

VPCs triggering VF that occur at different times in the same patient have similar morphologies suggesting similar sites of origin for the initial VPC of VF in each patient.

Ectopy in patients with permanent pacemakers and implantable cardioverter-defibrillators undergoing an MRI scan

BACKGROUND

Recent series suggest that magnetic resonance imaging (MRI) scanning can be performed safely in select patients with pacemakers or implantable cardioverter-defibrillators (ICDs). Limited data have been reported on ectopy during MRI scans in patients with pacemakers or ICDs. This study evaluated increased ectopy observed in patients with permanent pacemakers or ICDs undergoing MRI scanning of any landmark without peak specific absorption rate (SAR) limit.

METHODS

Fifty-two patients with a total of 119 leads underwent a total of 59 MRI scans of any landmark using usual protocols with standard peak SAR settings for the scan. No patient was pacemaker dependent. All devices were programmed to single-chamber demand mode (VVI) or dual-chamber demand mode (DDI) with a lower rate of 40 bpm.Both telemetry and pulse oximetry plethysmographic waveform were observed continuously throughout the scans for ectopy.

RESULTS

Increased ectopy was observed during seven scans. The ectopy in four scans was ventricular and had fixed coupling intervals of 1,500 and 3,000, and was likely due to device noise rejection behavior. The etiology of ectopy observed during the other three scans could not be determined. Ectopy could not be predicted by peak SAR, scan time duration, or landmark. No significant changes in pacing thresholds were seen postscan.

CONCLUSIONS

The current series suggests that a minority of patients with implanted pacemakers may have MRI-related ectopy. A significant proportion of this ectopy may arise from normal device behavior within the MRI environment.