Contact sensing provides a highly accurate means to titrate radiofrequency ablation lesion depth.

BACKGROUND: Transmural lesions are essential for efficacious ablation. There are, however, no accurate means to estimate lesion depth. OBJECTIVE: Explore use of the electrical coupling index (ECI) from the EnSite Contact™ System as a potential variable for lesion depth estimation. METHODS: Radiofrequency (RF) ablation lesions were created in atria and the thighs of swine using an irrigated RF catheter. Power was 30 W for 20 or 30 seconds intracardiac and 30-50 W for 10-60 seconds for the thigh. Intracardiac, the percentage change in ECI during ablation was compared with transmurality and collateral damage occurrence. For the thigh model, an algorithm estimating lesion depth was derived. Factors included: power, duration, and change in the ECI subcomponents (ΔECI+) during ablation. The ΔECI+ algorithm was compared to one using power and duration (PD) alone. RESULTS: Intracardiac, lesions with ≥12% reduction in ECI were more likely to be transmural (92.3% vs. 59.4%, P < 0.001). Twenty-second lesions were less likely to cause collateral damage compared to 30 seconds (33% vs. 70%, P = 0.003), while transmurality was similar. With the thigh model, ΔECI+ had a better correlation than the PD algorithm (P < 0.01). Accuracy of the ΔECI+ algorithm was unimproved with inclusion of tip orientation, while PD improved (R(2) = 0.64). DISCUSSION: Change in ECI provides evidence of transmural versus nontransmural swine intracardiac atrial lesions. A lesion depth estimation algorithm using ECI subcomponents is unaffected by tip orientation and is more accurate than using PD alone. CONCLUSION: Use of ECI as a factor in a lesion depth algorithm may provide clinically valuable information regarding the efficacy of intracardiac RF ablation lesions.

When is genetic testing useful in patients suspected to have inherited cardiac arrhythmias?

PURPOSE OF REVIEW: In this article, we will review the appropriate use of genetic testing in those patients suspected to have inherited arrhythmogenic diseases, with specific focus on the indications for testing and the expected probability of positive genotyping. RECENT FINDINGS: Important advances have been made in the identification of new genes, associated mutations, and polymorphisms that modulate susceptibility of acquired arrhythmias. We will examine the most recent advances relevant to the rational application of genetic analysis, guided by genotype-phenotype correlations derived from disease and patient-specific evaluation, as well as discussing novel technologies and recently published cost-effectiveness data. SUMMARY: Genetic analysis can be performed to identify the molecular substrate in those patients suspected to be affected by an inherited arrhythmogenic disease; however, the clinical usefulness of this information is often not straightforward. We hope to emphasize the concept that there is a significant difference in the impact of genetic testing within the various arrhythmogenic disorders, and the benefit of accessing genetic testing is not the same in all patients. The resultant integration between the expected yield of genetic screening and cost may allow the formation of criteria to prioritize access for those who could derive the most clinical benefit.

Pseudopolymorphic Wide Complex Tachycardia in a Child With Long QT Syndrome.

Implantable loop recorders (ILRs) can be a valuable tool in monitoring patients with inherited arrhythmia. This paper reports on a family with long QT syndrome (type 2 [LQT2]) in which a pseudopolymorphic wide complex tachycardia detected by ILR was ultimately diagnosed as a supraventricular aberrant rhythm, facilitated by noncompliance with beta-blocker therapy. (Level of Difficulty: Intermediate.).

Clinical spectrum of patients with a Brugada ECG.

PURPOSE OF REVIEW: The Brugada syndrome continues to spark intensive investigation since its earliest description. New insight has been gained regarding the genetic, histopathologic, and metabolic mechanisms of this heritable channelopathy - a heterogeneity that is reflected in the diverse clinical presentation. In this review, we will focus on clinical spectrum of patients with a Brugada ECG pattern with a special focus on diagnosis and risk stratification. RECENT FINDINGS: In the past year, multiple case reports have demonstrated that the Brugada ECG pattern is not limited to those with the diagnosed syndrome, with increasing evidence that an 'overlap' exists among inherited channelopathies, especially those involving the sodium and calcium channels. SUMMARY: The clinical spectrum of patients with a Brugada ECG remains broad, reflecting the heterogeneity of the underlying pathophysiology. As the true prevalence of the disease unfolds, knowledge regarding the clinical spectrum of patients with a Brugada ECG is important to implement effective risk stratification and management. It may be proposed that the ECG pattern of ST-segment elevation in the right precordial leads should not be seen as a marker of a specific syndrome, but rather as a common electrical expression of structural abnormalities in the right ventricle that may have genetic, infective, or inflammatory origins.

The genetics of cardiomyopathy: genotyping and genetic counseling.

Three decades of ongoing research into the identification of genes responsible for both cardiomyopathies and ion channel diseases has facilitated a progressive understanding of the pathophysiology of inherited arrhythmogenic diseases. Recent discoveries in the area of genetics promise to significantly change the current clinical practice of cardiology, as rapid advances in technology and a coincident reduction of costs associated with sequencing have pushed the "translation" of genomic information from bench to bedside. In turn, clinicians have at their disposal new tools for more accurate diagnosis of diseases, as well as for better calculation of health risks for affected families. It is clear, however, that the integration of genetic analysis into frontline clinical cardiology has not yet occurred, especially for heritable cardiomyopathic processes; no one simplified method exists for diagnosing these complex cardiac disease states. It therefore is important to assess the present and future roles of genetic analysis and counseling in clinical practice and how to assist the transition of genetic screening into current care to ensure the appropriate practical use of genetic tests in the routine clinical setting. The purpose of this discussion is to provide a concise review of recent developments in the field of heritable cardiomyopathies, with specific regard to genetic testing and genetic counseling.

Pacing Mediated Heart Rate Acceleration Improves Catheter Stability and Enhances Markers for Lesion Delivery in Human Atria During Atrial Fibrillation Ablation.

OBJECTIVES: This study sought to investigate the effect of pacing mediated heart rate modulation on catheter-tissue contact and impedance reduction during radiofrequency ablation in human atria during atrial fibrillation (AF) ablation. BACKGROUND: In AF ablation, improved catheter-tissue contact enhances lesion quality and acute pulmonary vein isolation rates. Previous studies demonstrate that catheter-tissue contact varies with ventricular contraction. The authors investigated the impact of modulating heart rate on the consistency of catheter-tissue contact and its effect on lesion quality. METHODS: Twenty patients undergoing paroxysmal AF ablation received ablation lesions at 15 pre-specified locations (12 left atria, 3 right atria). Patients were assigned randomly to undergo rapid atrial pacing for either the first half or the second half of each lesion. Contact force and ablation data with and without pacing were compared for each of the 300 ablation lesions. RESULTS: Compared with lesion delivery without pacing, pacing resulted in reduced contact force variability, as measured by contact force SD, range, maximum, minimum, and time within the pre-specified goal contact force range (p < 0.05). There was no difference in the mean contact force or force-time integral. Reduced contact force variability was associated with a 30% greater decrease in tissue impedance during ablation (p < 0.001). CONCLUSIONS: Pacing induced heart rate acceleration reduces catheter-tissue contact variability, increases the probability of achieving pre-specified catheter-tissue contact endpoints, and enhances impedance reduction during ablation. Modulating heart rate to improve catheter-tissue contact offers a new approach to optimize lesion quality in AF ablation. (The Physiological Effects of Pacing on Catheter Ablation Procedures to Treat Atrial Fibrillation [PEP AF]; NCT02766712).

Detection of phrenic nerves and their relation to cardiac anatomy using 64-slice multidetector computed tomography.

The improved temporal and spatial resolution allowed by multidetector computed tomography (MDCT) has facilitated the noninvasive assessment of cardiac anatomy before transcatheter electrophysiologic procedures. Clarification of spatial relations of phrenic nerves and key cardiac structures is important to decrease potential complications. The purpose of this study was to reconstruct the course of the right and left phrenic pericardiophrenic bundles and their relations to cardiac structures using 64-slice MDCT. One hundred six consecutive subjects (age 61 +/- 13 years; 39% women) who underwent self-referred coronary computed tomographic angiography using 64-slice MDCT underwent retrospective assessment of the phrenic nerves contained within the pericardiophrenic bundles. The course of the nerves was outlined in relation to the left atrial appendage, coronary sinus, and cardiac veins. The ability to individually detect the left and right phrenic nerves, as well as the frequency of direct contact between the left phrenic nerve and cardiac veins, was recorded. The left phrenic nerve was identified in 78 of 106 patients (74%). It crossed the left atrial appendage (n = 72, 91%), great cardiac vein (n = 63, 80%), posterior vein of the left ventricle (n = 39, 49%), posterior interventricular vein (n = 8, 10%), and anterior interventricular vein (n = 7, 9%). Mean Hounsfield units (HUs) of the left phrenic nerve was 81 +/- 25. The right phrenic nerve was identified in 50 of 106 patients (47%). Mean HUs of the right phrenic nerve were 94 +/- 26. In conclusion, cardiac imaging using 64-slice MDCT enabled adequate detection of the left and right phrenic nerves in relation to cardiac anatomy. In the setting of electrophysiologic interventions, MDCT before a procedure may elucidate anatomic relationships and help minimize inadvertent complications.

Utility of cardiac MRI in guiding revascularization therapy in unprotected left main stenosis: a case report.

Decision to select unprotected left main (ULM) stenting versus coronary artery bypass grafting surgery (CABG) depends on a multiplicity of factors, one of the most critical of which is myocardial viability. Delayed enhancement cardiac magnetic resonance (CMR) imaging has emerged as a useful means of comprehensively evaluating viable myocardium in postmyocardial infarct patients who require further revascularization. We present a patient with ULM stenosis in whom CMR imaging assisted in the decision to perform percutaneous coronary intervention over CABG.

Multilevel analyses of SCN5A mutations in arrhythmogenic right ventricular dysplasia/cardiomyopathy suggest non-canonical mechanisms for disease pathogenesis.

AIMS: Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy (ARVD/C) is often associated with desmosomal mutations. Recent studies suggest an interaction between the desmosome and sodium channel protein Nav1.5. We aimed to determine the prevalence and biophysical properties of mutations in SCN5A (the gene encoding Nav1.5) in ARVD/C. METHODS AND RESULTS: We performed whole-exome sequencing in six ARVD/C patients (33% male, 38.2 ± 12.1 years) without a desmosomal mutation. We found a rare missense variant (p.Arg1898His; R1898H) in SCN5A in one patient. We generated induced pluripotent stem cell-derived cardiomyocytes (hIPSC-CMs) from the patient's peripheral blood mononuclear cells. The variant was then corrected (R1898R) using Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 technology, allowing us to study the impact of the R1898H substitution in the same cellular background. Whole-cell patch clamping revealed a 36% reduction in peak sodium current (P = 0.002); super-resolution fluorescence microscopy showed reduced abundance of NaV1.5 (P = 0.005) and N-Cadherin (P = 0.026) clusters at the intercalated disc. Subsequently, we sequenced SCN5A in an additional 281 ARVD/C patients (60% male, 34.8 ± 13.7 years, 52% desmosomal mutation-carriers). Five (1.8%) subjects harboured a putatively pathogenic SCN5A variant (p.Tyr416Cys, p.Leu729del, p.Arg1623Ter, p.Ser1787Asn, and p.Val2016Met). SCN5A variants were associated with prolonged QRS duration (119 ± 15 vs. 94 ± 14 ms, P < 0.01) and all SCN5A variant carriers had major structural abnormalities on cardiac imaging. CONCLUSIONS: Almost 2% of ARVD/C patients harbour rare SCN5A variants. For one of these variants, we demonstrated reduced sodium current, Nav1.5 and N-Cadherin clusters at junctional sites. This suggests that Nav1.5 is in a functional complex with adhesion molecules, and reveals potential non-canonical mechanisms by which Nav1.5 dysfunction causes cardiomyopathy.

hERG Blockade by Iboga Alkaloids.

The iboga alkaloids are a class of naturally occurring and synthetic compounds, some of which modify drug self-administration and withdrawal in humans and preclinical models. Ibogaine, the prototypic iboga alkaloid that is utilized clinically to treat addictions, has been associated with QT prolongation, torsades de pointes and fatalities. hERG blockade as IKr was measured using the whole-cell patch clamp technique in HEK 293 cells. This yielded the following IC50 values: ibogaine manufactured by semisynthesis via voacangine (4.09 ± 0.69 µM) or by extraction from T. iboga (3.53 ± 0.16 µM); ibogaine's principal metabolite noribogaine (2.86 ± 0.68 µM); and voacangine (2.25 ± 0.34 µM). In contrast, the IC50 of 18-methoxycoronaridine, a product of rational synthesis and current focus of drug development was >50 µM. hERG blockade was voltage dependent for all of the compounds, consistent with low-affinity blockade. hERG channel binding affinities (K i) for the entire set of compounds, including 18-MC, ranged from 0.71 to 3.89 µM, suggesting that 18-MC binds to the hERG channel with affinity similar to the other compounds, but the interaction produces substantially less hERG blockade. In view of the extended half-life of noribogaine, these results may relate to observations of persistent QT prolongation and cardiac arrhythmia at delayed intervals of days following ibogaine ingestion. The apparent structure-activity relationships regarding positions of substitutions on the ibogamine skeleton suggest that the iboga alkaloids might provide an informative paradigm for investigation of the structural biology of the hERG channel.

Use of whole exome sequencing for the identification of Ito-based arrhythmia mechanism and therapy.

BACKGROUND: Identified genetic variants are insufficient to explain all cases of inherited arrhythmia. We tested whether the integration of whole exome sequencing with well-established clinical, translational, and basic science platforms could provide rapid and novel insight into human arrhythmia pathophysiology and disease treatment. METHODS AND RESULTS: We report a proband with recurrent ventricular fibrillation, resistant to standard therapeutic interventions. Using whole-exome sequencing, we identified a variant in a previously unidentified exon of the dipeptidyl aminopeptidase-like protein-6 (DPP6) gene. This variant is the first identified coding mutation in DPP6 and augments cardiac repolarizing current (Ito) causing pathological changes in Ito and action potential morphology. We designed a therapeutic regimen incorporating dalfampridine to target Ito. Dalfampridine, approved for multiple sclerosis, normalized the ECG and reduced arrhythmia burden in the proband by >90-fold. This was combined with cilostazol to accelerate the heart rate to minimize the reverse-rate dependence of augmented Ito. CONCLUSIONS: We describe a novel arrhythmia mechanism and therapeutic approach to ameliorate the disease. Specifically, we identify the first coding variant of DPP6 in human ventricular fibrillation. These findings illustrate the power of genetic approaches for the elucidation and treatment of disease when carefully integrated with clinical and basic/translational research teams.

Genetic Testing for Cardiac Arrhythmias: Ready for Prime Time?

Despite the heterogeneity of substrates and clinical expressivity, genetic testing has a direct impact on clinical practice: it allows a specific diagnosis, including silent carriers (ie, asymptomatic diagnosis) and, in select diseases, the identification of a mutation has major impact for risk stratification and treatment of patients. This article addresses the role of genetic testing for each of the most epidemiologically relevant inherited arrhythmogenic diseases, specifically long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy.

Successful catheter ablation of focal ventricular fibrillation originating from the right ventricle.

Sudden cardiac death from ventricular fibrillation (VF) typically occurs in patients with structural heart disease, but in 5 to 10 percent VF is "idiopathic," occurring in normal hearts. Recently, there has been the description and growing recognition of patients with VF that has a focal origin, the common sites being in the right ventricular outflow tract (RVOT) and sites in the left ventricle. A focus within the right ventricle outside the RVOT is rare. We present a case of a woman with VF storm that was localized to the inferobasal right ventricle and was successfully treated with radiofrequency ablation.

Anesthetic management of thoracic trauma.

PURPOSE OF REVIEW: Trauma remains a leading cause of death across all age groups. Thoracic injury is a contributing cause in approximately half of these. Despite being potentially life threatening, most thoracic trauma is managed nonoperatively or with an intercostal catheter. Only 10% of thoracic trauma patients will require emergency thoracotomy. Many more will undergo emergency or urgent surgical intervention for coexisting injuries. Thoracic injuries are dynamic. It is crucial for the anesthesiologist to continually reassess the patient, so that the manifestations of evolving injuries may be detected as early as possible and appropriate management decisions made. Up-to-date knowledge of injury patterns, mechanisms, pathophysiology, and operative and nonoperative management will facilitate optimal management of these patients. RECENT FINDINGS: There is recent literature discussing the surgical, anesthetic and critical care management of a range of thoracic injuries resulting from either blunt or penetrating trauma. SUMMARY: Initial resuscitation and surgical management of patients with thoracic trauma continue to evolve. Improvements in prehospital care and diagnostic techniques as well as development of minimally invasive interventions mean that the anesthesiologist may be required to provide care to unstable patients in an expanded range of scenarios and environments.