Routine scheduled angiographic follow‐up (SAF) after percutaneous coronary intervention (PCI) has been associated with a higher rate of target vessel revascularization (TVR). Its benefits are not ...known. SAF at 13 months after ST‐segment elevation myocardial infarction (STEMI) was planned in the first 1,800 successfully stented patients enrolled in the Harmonizing Outcomes with RevascularIZatiON and Stents in Acute Myocardial Infarction (HORIZONS‐AMI) trial. We compared the outcomes of patients with and without SAF at 1 year (before SAF) and at 3 years (after SAF). There were 1,197 patients (66.5% of expected) with and 2,207 patients without SAF. Prior to SAF, the 1‐year composite rate of death or myocardial infarction (MI) was not significantly different between the 2 groups (2.7% vs. 3.9%, respectively, P = 0.06), although the rate of death was lower (0.1% vs. 2.2%, P < 0.0001), nor were there differences in the 1‐year rates of TVR, stent thrombosis or major adverse cardiac and cerebral events). At 3 years, death or MI rates were again similar between the groups (8.3% vs. 9.5%, P = 0.22), but TVR was more common in the SAF group (17.0% vs. 8.6%, P < 0.0001), due to an increase in TVR at time of SAF. In the SAF group, patients in whom TVR was performed before or after the 13‐month SAF window had markedly higher 3‐year rates of MI and stent thrombosis than patients in whom TVR was performed during SAF or not at all. In conclusion, SAF after primary PCI in STEMI is associated with doubling of the rate of revascularization without an improvement in death or MI, and therefore cannot be recommended.
Background: Inherited loss of function mutations in SCN5A have been linked to overlapping syndromes including cardiac conduction disease and Brugada syndrome (BrS). The mechanisms responsible for the ...development of one without the other are poorly understood.
Methods: Direct sequencing was performed in a family with cardiac conduction disease. Wild‐type (WT) and mutant channels were expressed in TSA201 cells for electrophysiological study. Green fluorescent protein (GFP)‐fused WT or mutant genes were used to assess channel trafficking.
Results: A novel SCN5A mutation, P1008S, was identified in all family members displaying first‐degree atrioventricular block, but not in unaffected family members nor in 430 reference alleles. Peak P1008S current was 11.77% of WT (P < 0.001). Confocal microscopy showed that WT channels tagged with GFP were localized on the cell surface, whereas GFP‐tagged P1008S channels remained trapped in intracellular organelles. Trafficking could be rescued by incubation at room temperature, but not by incubation with mexiletine (300 μM) at 37°C. We also identified a novel polymorphism (D601E) in CACNB2b that slowed inactivation of L‐type calcium current (ICa,L), significantly increased total charge. Using the Luo‐Rudy action potential (AP) model, we show that the reduction in sodium current (INa) can cause loss of the right ventricular epicardial AP dome in the absence but not in the presence of the slowed inactivation of ICa,L. Slowed conduction was present in both cases.
Conclusions: Our results suggest genetic variations leading to a loss‐of‐function in INa coupled with a gain of function in ICa,L may underlie the development of cardiac conduction disease without BrS. (PACE 2010; 33:274–285)
The autonomic nervous system has been implicated in several arrhythmogenic diseases, including long QT syndrome type 3 (LQT3) and Brugada syndrome. Scarce information on the cellular components of ...the intrinsic cardiac ganglia from higher mammals has limited our understanding of the role of the autonomic nervous system in such diseases.
The purpose of this study was to isolate and characterize the electrophysiologic properties of canine intracardiac neurons.
Action potentials (APs) and ionic currents were studied in enzymatically dissociated canine intracardiac neurons under current and voltage clamp conditions. Immunohistochemical and reverse transcription-polymerase chain reaction analysis was performed using freshly isolated intracardiac ganglia.
APs recorded from intracardiac neurons displayed a tetrodotoxin-resistant (TTX-R) component. TTX-R APs were abolished in the absence of sodium but persisted in the absence of external calcium. Immunohistochemical studies showed the presence of TTX-R sodium channels in these ganglia. Sodium currents were characterized by two components with different affinities for TTX: a tetrodotoxin-sensitive (TTX-S) component and a TTX-R component. TTX-S current inactivation was characteristic of neuronal sodium currents, whereas TTX-R current inactivation time constants were similar to those previously reported for Na(v)1.5 channels. TTX sensitivity (IC(50) = 1.17 microM) of the TTX-R component was in the range reported for Na(v)1.5 channels. Expression of Na(v)1.5 channels in intracardiac ganglia was confirmed by PCR analysis and sequencing.
Our results suggest that canine intracardiac neurons functionally express Na(v)1.5 channels. These findings open an exciting new door to our understanding of autonomically modulated arrhythmogenic diseases linked to mutations in Na(v)1.5 channels, including Brugada syndrome and LQT3.
The Brugada syndrome (BS) is characterized by ST segment elevation in the right precordial leads and sudden cardiac death. The disease is linked to mutations in SCN5A in approximately 20% of cases. ...We collected a large family with BS and have identified a novel intronic mutation. We performed the clinical, genetic, molecular and biophysical characterization of this disease-causing mutation. With direct sequencing we identified an intronic insertion of TGGG 5 bp from the end of the Exon 27 of SCN5A. For transcript analysis, we investigated Epstein–Barr-transformed lymphoblastoid cell lines from patients and controls. Total RNA was extracted and RT-PCR experiments were performed to analyze the splicing patterns in exon 27 and 28. We identified two bands, one of the expected size and the other which showed a 96 bp deletion in exon 27, leading to a 32 amino acid in-frame deletion involving segments 2 and 3 of Domain IV of the SCN5A protein. This finding indicates that the intronic mutation creates a cryptic splice site inside Exon 27. Biophysical analysis using whole-cell patch-clamp techniques showed a complete loss of function of the mutated channels when heterologously expressed. In summary, this is the first report of a dysfunctional sodium channel created by an intronic mutation giving rise to cryptic splice site activation in SCN5A in a family with the BS. The deletion of fragments of segments 2 and 3 of Domain IV leads to complete loss of function, consistent with the biophysical data found in several mutations causing BS.
Introduction: Long QT Syndrome (LQTS) is an inherited disorder characterized by prolonged QT intervals and life‐threatening polymorphic ventricular tachyarrhythmias. LQT1 caused by KCNQ1 mutations is ...the most common form of LQTS.
Methods and Results: Patients diagnosed with LQTS were screened for disease‐associated mutations in KCNQ1, KCNH2, KCNE1, KCNE2, KCNJ2, and SCN5A. A novel mutation was identified in KCNQ1 caused by a three‐base deletion at the position 824–826, predicting a deletion of phenylalanine at codon 275 in segment 5 of KCNQ1 (ΔF275). Wild‐type (WT) and ΔF275‐KCNQ1 constructs were generated and transiently transfected together with a KCNE1 construct in CHO‐K1 cells to characterize the properties of the slowly activating delayed rectifier current (IKs) using conventional whole‐cell patch–clamp techniques. Cells transfected with WT‐KCNQ1 and KCNE1 (1:1.3 molar ratio) produced slowly activating outward current with the characteristics of IKs. Tail current density measured at −40 mV following a two‐second step to +60 mV was 381.3 ± 62.6 pA/pF (n = 11). Cells transfected with ΔF275‐KCNQ1 and KCNE1 exhibited essentially no current. (Tail current density: 0.8 ± 2.1 pA/pF, n = 11, P = 0.00001 vs WT). Cotransfection of WT‐ and ΔF275‐ KCNQ1 (50/50), along with KCNE1, produced little to no current (tail current density: 10.3 ± 3.5 pA/pF, n = 11, P = 0.00001 vs WT alone), suggesting a potent dominant negative effect. Immunohistochemistry showed normal membrane trafficking of ΔF275‐KCNQ1.
Conclusion: Our data suggest that a ΔF275 mutation in KCNQ1 is associated with a very potent dominant negative effect leading to an almost complete loss of function of IKs and that this defect underlies a LQT1 form of LQTS.
A Mutation in the β3 Subunit of the Cardiac Sodium Channel Associated With Brugada ECG Phenotype
Dan Hu, MD, PhD ;
Hector Barajas-Martinez, PhD ;
Elena Burashnikov, BS ;
Michael Springer, MD ;
...Yuesheng Wu, MD ;
Andras Varro, MD, PhD ;
Ryan Pfeiffer, BS ;
Tamara T. Koopmann, PhD ;
Jonathan M. Cordeiro, PhD ;
Alejandra Guerchicoff, PhD ;
Guido D. Pollevick, PhD and
Charles Antzelevitch, PhD
From the Masonic Medical Research Laboratory (D.H., H.-B.M., E.B., Y.W., R.P., J.M.C., A.G., G.D.P., C.A.), Utica, NY; Cardiology Department (M.S.), University of Louisville, Louisville, Ky; Heart Failure Research Center (T.T.K.), Academic Medical Center Amsterdam, The Netherlands; Department of Pharmacology and Pharmacotherapy (A.V.), University of Szeged, Szeged, Hungary; and Division for Cardiovascular Pharmacology (A.V.), Hungarian Academy of Sciences, Szeged, Hungary.
Correspondence to Charles Antzelevitch, PhD, Masonic Medical Research Laboratory, 2150 Bleecker St, Utica, NY. E-mail ca{at}mmrl.edu
Received October 15, 2008; accepted April 20, 2009.
Background— Brugada syndrome, characterized by ST-segment elevation in the right precordial ECG leads and the development of life-threatening ventricular arrhythmias, has been associated with mutations in 6 different genes. We identify and characterize a mutation in a new gene.
Methods and Results— A 64-year-old white male displayed a type 1 ST-segment elevation in V1 and V2 during procainamide challenge. Polymerase chain reaction-based direct sequencing was performed using a candidate gene approach. A missense mutation (L10P) was detected in exon 1 of SCN3B , the β3 subunit of the cardiac sodium channel, but not in any other gene known to be associated with Brugada syndrome or in 296 controls. Wild-type (WT) and mutant genes were expressed in TSA201 cells and studied using whole-cell patch-clamp techniques. Coexpression of SCN5A /WT+ SCN1B /WT+ SCN3B /L10P resulted in an 82.6% decrease in peak sodium current density, accelerated inactivation, slowed reactivation, and a –9.6-mV shift of half-inactivation voltage compared with SCN5A /WT+ SCN1B /WT+ SCN3B /WT. Confocal microscopy revealed that SCN5A /WT channels tagged with green fluorescent protein are localized to the cell surface when coexpressed with WT SCN1B and SCN3B but remain trapped in intracellular organelles when coexpressed with SCN1B /WT and SCN3B /L10P. Western blot analysis confirmed the presence of Na V β3 in human ventricular myocardium.
Conclusions— Our results provide support for the hypothesis that mutations in SCN3B can lead to loss of transport and functional expression of the hNa v 1.5 protein, leading to reduction in sodium channel current and clinical manifestation of a Brugada phenotype.
Key Words: Brugada syndrome arrhythmia ion channels SCN3B protein trafficking
CLINICAL PERSPECTIVE
Mosquitocidal Bacillus thuringiensis strains show as a common feature the presence of toxic proteins with cytolytic and hemolytic activities, Cyt1Aa1 being the characteristic cytolytic toxin of ...Bacillus thuringiensis subsp. israelensis. We have detected the presence of another cyt gene in this subspecies, highly homologous to cyt2Aa1, coding for the 29-kDa cytolytic toxin from B. thuringiensis subsp. kyushuensis. This gene, designated cyt2Ba1, maps upstream of cry4B coding for the 130-kDa crystal toxin, on the 72-MDa plasmid of strain 4Q2-72. Sequence analysis revealed, as a remarkable feature, a 5' mRNA stabilizing region similar to those described for some cry genes. PCR amplification and Southern analysis confirmed the presence of this gene in other mosquitocidal subspecies. Interestingly, anticoleopteran B. thuringiensis subsp. tenebrionis belonging to the morrisoni serovar also showed this gene. On the other hand, negative results were obtained with the anti-lepidopteran strains B. thuringiensis subsp. kurstaki HD-1 and subsp. aizawai HD-137. Western analysis failed to reveal Cyt2A-related polypeptides in B. thuringiensis subsp. israelensis 4Q2-72. However, B. thuringiensis subsp. israelensis 1884 and B. thuringiensis subsp. tenebrionis did show cross-reactive products, although in very small amounts
We cloned and sequenced a new sytolysin gene from Bacillus thuringiensis subsp. medellin. Three IS240-like insertion sequence elements and the previously cloned cyt1Ab and p21 genes were found in the ...vicinity of the cytolysin gene.
PDF
