SCN5A(K817E), a novel Brugada syndrome-associated mutation that alters the activation gating of NaV1.5 channel.

BACKGROUND: Brugada syndrome (BrS) is an inherited lethal arrhythmic disorder characterized by syncope and sudden cardiac death from ventricular tachyarrhythmias. Here we identified a novel K817E mutation of SCN5A gene in a man with type 1 BrS electrocardiogram pattern using next-generation sequencing targeted for 73 cardiac disorder-related genes. SCN5A encodes the α-subunit of NaV1.5 voltage-gated Na(+) channel, and some of its mutations are linked to BrS. The proband had no mutation in any of the other arrhythmia-related genes sequenced. OBJECTIVE: We investigated whether the K817E mutation causes a functional change of NaV1.5 channel responsible for the BrS phenotype. METHODS: We compared the electrophysiological properties of the whole-cell currents mediated by wild-type and mutant channels heterologously expressed in human embryonic kidney 293 cells by using a voltage-clamp technique. RESULTS: The K817E mutation reduced the Na(+) current density by 39.0%-91.4% at membrane potentials from -55 to -5 mV. This reduction resulted from a ~24-mV positive shift in the voltage dependence of activation. The mutation also decelerated recovery from both fast and intermediate inactivation, whereas it had little effect on the cell surface expression, single-channel conductance, voltage-dependence of fast inactivation, entry into intermediate inactivation, use-dependent loss of channel availability, or closed-state inactivation. CONCLUSION: The K817E mutation of SCN5A gene leads to loss of function of NaV1.5 channel and may underlie the BrS phenotype of the proband.

Electrophysiological and anatomical differences of the slow pathway between the fast-slow form and slow-slow form of atrioventricular nodal reentrant tachycardia.

AIMS: This study aimed to clarify whether electrophysiological and anatomical properties of the slow pathway (SP) could be different between the fast-slow form (F/S) and the slow-slow form (S/S) atrioventricular nodal reentrant tachycardia (AVNRT). METHODS AND RESULTS: Nine patients with F/S and 15 patients with S/S of atypical AVNRT were studied. The patients with S/S were divided into two groups; those with the anterograde SP being eliminated (S/S aSP-E) or preserved (S/S aSP-P) during catheter ablation. HA (CS-His) was determined as the difference of the shortest HA interval between the His bundle region and the coronary sinus (CS) region. The ratio of the amplitudes of atrial and ventricular potential (A/V ratio) of the successful ablation site of the SP was also evaluated. Effective refractory period of the retrograde SP was shorter and HA intervals during both tachycardia and ventricular pacing were longer in F/S than in S/S. HA (CS-His) did not differ between F/S and S/S (-4.3 ± 20.2 vs.-4.4 ± 18.4 ms, NS). The A/V ratio was significantly greater in the S/S aSP-P group compared with the both groups of F/S and S/S aSP-E (0.83 ± 0.29 vs. 0.38 ± 0.09 and 0.26 ± 0.15 ms, P < 0.01). CONCLUSION: Properties of the retrograde SP differ between F/S and S/S of AVNRT. Fast-slow form may utilize the same pathway for the retrograde conduction as the anterograde SP in S/S.

Mechanisms of atrial tachyarrhythmias associated with coronary artery occlusion in a chronic canine model.

BACKGROUND: Coronary artery disease predisposes to atrial fibrillation (AF), but the effects of chronic atrial ischemia/infarction on AF-related substrates are unknown. METHODS AND RESULTS: Regional right atrial myocardial infarction (MI) was created in 40 dogs by ligating an artery that supplies the right atrial free wall and not the ventricles; 35 sham dogs with the same artery isolated but not ligated were controls. Dogs were observed 8 days after MI and subjected to open-chest study, in vitro optical mapping, and/or cell isolation for patch-clamp and Ca(2+) imaging on day 8. Holter ECGs showed more spontaneous atrial ectopy in MI dogs (eg, 662±281 on day 7 versus 34±25 ectopic complexes per day at baseline; 52±21 versus 1±1 atrial tachycardia episodes per day). Triggered activity was increased in MI border zone cells, which had faster decay of caffeine-evoked Ca(2+) transients and enhanced (by ≈73%) Na(+)-Ca(2+) exchange current. Spontaneous Ca(2+) sparks (confocal microscopy) occurred under ß-adrenergic stimulation in more MI dog cells (66±9%) than in control cells (29±4%; P<0.01). Burst pacing induced long-lasting AF in MI dogs (1146±259 versus 30±14 seconds in shams). Increased border zone conduction heterogeneity was confirmed by both bipolar electrode mapping in vivo and optical mapping. Optical mapping demonstrated stable border zone reentry in all 9 MI preparations but in none of 6 shams. Border zone tissue showed increased fibrous tissue content. CONCLUSIONS: Chronic atrial ischemia/infarction creates substrates for both spontaneous ectopy (Ca(2+)-release events, increased Na(+)-Ca(2+) exchange current) and sustained reentry (conduction abnormalities that anchor reentry). Thus, chronic atrial infarction in dogs promotes both AF triggers and the substrate for AF maintenance. These results provide novel insights into potential AF mechanisms in patients with coronary artery disease.

Roles of the left atrial roof and pulmonary veins in the anatomic substrate for persistent atrial fibrillation and ablation in a canine model.

OBJECTIVES: the aim of this study was to establish the electrophysiological consequences of pulmonary vein encircling ablation (PVEA) and linear left atrial roof ablation (LARA) for the atrial fibrillation (AF) substrate in an experimental model. BACKGROUND: sequential application of ablation lesions is often used in the management of AF, almost always incorporating PVEA and LARA. METHODS: Atrial tachypacing (400 beats/min, 5 weeks) was used to create an AF substrate in 13 dogs. PVEA and LARA were applied in randomized order. Regional atrial refractoriness, AF vulnerability, AF duration, and activation during AF were assessed before and after applying ablation lesion sets. RESULTS: PVEA failed to terminate AF or affect AF duration (742 ± 242 s before vs. 627 ± 227 s after PVEA) but decreased AF vulnerability to single extrastimuli from 91 ± 4% to 59 ± 5% (p < 0.001) by increasing effective refractory periods at sites with suppressed AF induction (from 78 ± 4 ms to 102 ± 8 ms, p < 0.01). LARA terminated AF in 67% of dogs (p < 0.05 vs. PVEA) and reduced AF duration (from 934 ± 232 s to 322 ± 183 s, p < 0.01) without affecting AF vulnerability. Baseline AF mapping showed left atrial (LA)-dominant complex reactivations (LA 9.4 ± 0.9 vs. right atrial 1.1 ± 0.3 reactivations/500-ms window, p < 0.001), with the LA roof frequently involved in re-entry circuits (44 ± 9% of LA reactivations). LARA terminated AF by interrupting LA roof reactivation circuits. In 5 of 13 cases, macro-re-entrant tachycardias (usually perimitral) occurred after LARA eliminated persistent AF. CONCLUSIONS: both PVEA and LARA had beneficial but limited actions in this canine model. LARA suppressed AF perpetuation by interrupting LA roof reactivation, without affecting AF vulnerability. PVEA suppressed AF initiation by prolonging regional effective refractory period but failed to affect the AF-perpetuating substrate. These findings indicate the need to systematically study individual stepwise components to refine AF ablation procedures.

Changes in connexin expression and the atrial fibrillation substrate in congestive heart failure.

RATIONALE: Although connexin changes are important for the ventricular arrhythmic substrate in congestive heart failure (CHF), connexin alterations during CHF-related atrial arrhythmogenic remodeling have received limited attention. OBJECTIVE: To analyze connexin changes and their potential contribution to the atrial fibrillation (AF) substrate during the development and reversal of CHF. METHODS AND RESULTS: Three groups of dogs were studied: CHF induced by 2-week ventricular tachypacing (240 bpm, n=15); CHF dogs allowed a 4-week nonpaced recovery interval after 2-week tachypacing (n=16); and nonpaced sham controls (n=19). Left ventricular (LV) end-diastolic pressure and atrial refractory periods increased with CHF and normalized on CHF recovery. CHF caused abnormalities in atrial conduction indexes and increased the duration of burst pacing-induced AF (DAF, from 22+/-7 seconds in control to 1100+/-171 seconds, P<0.001). CHF did not significantly alter overall atrial connexin (Cx)40 and Cx43 mRNA and protein expression levels, but produced Cx43 dephosphorylation, increased Cx40/Cx43 protein expression ratio and caused Cx43 redistribution toward transverse cell-boundaries. All of the connexin-alterations reversed on CHF recovery, but CHF-induced conduction abnormalities and increased DAF (884+/-220 seconds, P<0.001 versus control) remained. The atrial fibrous tissue content increased from 3.6+/-0.7% in control to 14.7+/-1.5% and 13.3+/-2.3% in CHF and CHF recovery, respectively (both P<0.01 versus control), with transversely running zones of fibrosis physically separating longitudinally directed muscle bundles. In an ionically based action potential/tissue model, fibrosis was able to account for conduction abnormalities associated with CHF and recovery. CONCLUSIONS: CHF causes atrial connexin changes, but these are not essential for CHF-related conduction disturbances and AF promotion, which are rather related primarily to fibrotic interruption of muscle bundle continuity.

Enalapril preserves sinus node function in a canine atrial fibrillation model induced by rapid atrial pacing.

METHODS AND RESULTS: Seventeen beagles were pretreated with either placebo (group I, n = 9) or enalapril 1 mg/kg/day (group II, n = 8) and paced at 500/min from the right atrial appendage for 4 weeks. Every week, corrected sinus node recovery time (CSNRT) and sinus cycle length (SCL) were measured. Quantitative analysis of interstitial fibrosis (IF) and adipose tissue (AT) in the SN was performed with Masson's trichrome stain, and apoptosis of the sinus nodal cells were detected with terminal deoxynucleotidyl transferase nick end-labeling. In group I, rapid atrial pacing prolonged both CSNRT and SCL. After 4 weeks of pacing, CSNRT and SCL were significantly shorter in group II (CSNRT, 410 +/- 37 msec; SCL, 426 +/- 34 msec) than in group I (CSNRT, 717 +/- 52 msec, P < 0.005; SCL, 568 +/- 73 msec, P < 0.05). Both IF and AT of the SN were greater in group I (IF, 9.7 +/- 1.9%; AT, 32.6 +/- 5.9%) than in seven sham dogs (IF, 2.4 +/- 0.9%, P < 0.05; AT, 4.0 +/- 1.7%, P < 0.05) and in group II dogs (IF, 4.0 +/- 2.0%, P < 0.05; AT, 4.0 +/- 1.7%, P < 0.05). End-labeling assay was positive in three of nine dogs in group I, but negative in group II and sham dogs. CONCLUSIONS: Rapid atrial pacing impaired SN function through IF and AT of the SN. Enalapril prevented these pacing-induced degenerative changes and improved SN function.

Vagal activity modulates spontaneous augmentation of ST elevation in the daily life of patients with Brugada syndrome.

INTRODUCTION: In Brugada syndrome, ventricular fibrillation (VF) occurs mainly during sleep, and Brugada ECG signs are intensified by parasympathomimetic drugs; therefore, vagal activity could be a precipitating factor of VF. The aim of the present study was to elucidate the relation between spontaneous augmentation of ST elevation and changes in autonomic nervous activities in the daily life of patients with Brugada syndrome. METHODS AND RESULTS: Twenty-three consecutive patients with Brugada syndrome were studied. Group VF(+) consisted of 7 symptomatic patients and 3 asymptomatic patients with inducible VF; group VF(-) consisted of 13 asymptomatic patients without documented or inducible VF. Two-channel unipolar lead (V(1) and V(2)) Holter ECG was recorded. Heart rate variability was analyzed by the maximum entropy method. Spontaneous augmentation of ST elevation (>/=1.5 mm/20 min) occurred more frequently during 24 hours in group VF(+) than in group VF(-) (5.7 +/- 2.5 times vs 2.3 +/- 2.4 times, P < 0.01). ST elevation was significantly greater in group VF(+) than in group VF(-) (2.1 +/- 0.2 mm vs 1.8 +/- 0.2 mm, P < 0.05). Power of the high-frequency component (HF: 0.15-0.4 Hz) and RR interval increased progressively, and the ratio of low-frequency component (LF; 0.04- 0.15 Hz) to high-frequency component (LF/HF) gradually decreased toward the time of maximum ST elevation. During an entire day, daytime (0-5 P.M.), and nighttime (0-5 A.M.), both HF and LF/HF were not different between groups VF(+) and VF(-). CONCLUSION: In Brugada syndrome, spontaneous augmentation of ST elevation in daily life occurred along with an increase in vagal activity. ST elevation was augmented more in patients with VF than in those without VF under similar vagal tone.

Entrainment mapping of dual-loop macroreentry in common atrial flutter: new insights into the atrial flutter circuit.

INTRODUCTION: The aim of this study was to determine using entrainment mapping whether the reentrant circuit of common type atrial flutter (AFL) is single loop or dual loop. METHODS AND RESULTS: In 12 consecutive patients with counterclockwise (CCW) AFL, entrainment mapping was performed with evaluation of atrial electrograms from the tricuspid annulus (TA) and the posterior right atrial (RA) area. We hypothesized that a dual-loop reentry could be surmised from "paradoxical delayed capture" of the proximal part of the circuit having a longer interval from the stimulus to the captured beat compared with the distal part of the circuit. In 6 of 12 patients with CCW AFL, during entrainment from the septal side of the posterior blocking line, the interval from the stimulus to the last captured beat was longer at the RA free wall than at the isthmus position. In these six patients with paradoxical delayed capture, flutter cycle length (FCL) was 227 +/- 12 ms and postpacing interval minus FCL was significantly shorter at the posterior blocking line than at the RA free wall (20 +/- 11 ms vs 48 +/- 33 ms, P < 0.05). In two of these patients, early breakthrough occurred at the lateral TA. A posterior block line was confirmed in all six patients in the sinus venosa area by intracardiac echocardiography. CONCLUSION: Half of the patients with common type AFL had a dual-loop macroreentrant circuit consisting of an anterior loop (circuit around the TA) and a posterior loop (circuit around the inferior vena cava and the posterior blocking line).

Complex atrial reentrant circuits evaluated by entrainment mapping using a multielectrode basket catheter.

Atrial tachycardias after open heart surgery sometimes have complex reentrant circuits. A patient with a dual-loop atrial reentrant circuit occurring after mitral valve replacement was evaluated by entrainment mapping with a basket catheter. The position of the catheter was adjusted to obtain atrial electrograms of the anterior and posterior septal areas, the crista terminalis, the free wall, and the tricuspid annular region. Entrainment mapping identified a dual-loop reentry consisting of one circuit around the tricuspid annulus and another around the septal atriotomy scar. The reentrant circuit around the septal incision was eliminated by ablating the area between the septal incision and the inferior vena cava, and the circuit around the tricuspid annulus was terminated with an additional linear ablation between the tricuspid annulus and the inferior vena cava. Entrainment mapping using a multielectrode basket catheter is very useful for identifying complex atrial reentrant circuits.