Kunihiro Nishida

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.

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.

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 Ca2+ 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 Ca2+ transients and enhanced (by ≈73%) Na+-Ca2+ exchange current. Spontaneous Ca2+ sparks (confocal microscopy) occurred under &bgr;-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 (Ca2+-release events, increased Na+-Ca2+ 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.

Multiple Potential Molecular Contributors to Atrial Hypocontractility Caused by Atrial Tachycardia Remodeling in Dogs

Background—Atrial fibrillation impairs atrial contractility, inducing atrial stunning that promotes thromboembolic stroke. Action potential (AP)-prolonging drugs are reported to normalize atrial hypocontractility caused by atrial tachycardia remodeling (ATR). Here, we addressed the role of AP duration (APD) changes in ATR-induced hypocontractility. Methods and Results—ATR (7-day tachypacing) decreased APD (perforated patch recording) by ≈50%, atrial contractility (echocardiography, cardiomyocyte video edge detection), and [Ca2+]i transients. ATR AP waveforms suppressed [Ca2+]i transients and cell shortening of control cardiomyocytes; whereas control AP waveforms improved [Ca2+]i transients and cell shortening in ATR cells. However, ATR cardiomyocytes clamped with the same control AP waveform had ≈60% smaller [Ca2+]i transients and cell shortening than control cells. We therefore sought additional mechanisms of contractile impairment. Whole-cell voltage clamp revealed reduced ICaL; ICaL inhibition superimposed on ATR APs further suppressed [Ca2+]i transients in control cells. Confocal microscopy indicated ATR-impaired propagation of the Ca2+ release signal to the cell center in association with loss of t-tubular structures. Myofilament function studies in skinned permeabilized cardiomyocytes showed altered Ca2+ sensitivity and force redevelopment in ATR, possibly due to hypophosphorylation of myosin-binding protein C and myosin light-chain protein 2a (immunoblot). Hypophosphorylation was related to multiple phosphorylation system abnormalities where protein kinase A regulatory subunits were downregulated, whereas autophosphorylation and expression of Ca2+-calmodulin-dependent protein kinase II&dgr; and protein phosphatase 1 activity were enhanced. Recovery of [Ca2+]i transients and cell shortening occurred in parallel after ATR cessation. Conclusions—Shortening of APD contributes to hypocontractility induced by 1-week ATR but accounts for it only partially. Additional contractility-suppressing mechanisms include ICaL current reduction, impaired subcellular Ca2+ signal transmission, and altered myofilament function associated with abnormal myosin and myosin-associated protein phosphorylation. The complex mechanistic basis of the atrial hypocontractility associated with AF argues for upstream therapeutic targeting rather than interventions directed toward specific downstream pathophysiological derangements.

Differential Protein Kinase C Isoform Regulation and Increased Constitutive Activity of Acetylcholine-Regulated Potassium Channels in Atrial Remodeling

Rationale: Atrial fibrillation (AF) causes atrial-tachycardia remodeling (ATR), with enhanced constitutive acetylcholine-regulated K+ current (IKAChC) contributing to action potential duration shortening and AF promotion. The underlying mechanisms are unknown. Objective: To evaluate the role of protein-kinase C (PKC) isoforms in ATR-induced IKAChC activation. Methods and Results: Cells from ATR-dogs (400-bpm atrial pacing for 1 week) were compared to control dog cells. In vitro tachypaced (TP; 3 Hz) canine atrial cardiomyocytes were compared to parallel 1-Hz paced cells. IKAChC single-channel activity was assessed in cell-attached and cell-free (inside-out) patches. Protein expression was assessed by immunoblot. In vitro TP activated IKAChC, mimicking effects of in vivo ATR. Discrepant effects of PKC activation and inhibition between control and ATR cells suggested isoform-selective effects and altered PKC isoform distribution. Conventional PKC isoforms (cPKC; including PKC&agr;) inhibited, whereas novel isoforms (including PKC&egr;) enhanced, acetylcholine-regulated K+ current (IKACh) in inside-out patches. TP and ATR downregulated PKC&agr; (by 33% and 37%, respectively) and caused membrane translocation of PKC&egr;, switching PKC predominance to the stimulatory novel isoform. TP increased [Ca2+]i at 2 hours by 30%, with return to baseline at 24 hours. Buffering [Ca2+]i during TP with the cell-permeable Ca2+ chelator BAPTA-AM (1 &mgr;mol/L) or inhibiting the Ca2+-dependent protease calpain with PD150606 (20 &mgr;mol/L) prevented PKC&agr; downregulation and TP enhancement of IKAChC. PKC&egr; inhibition with a cell-permeable peptide inhibitor suppressed TP/ATR-induced IKAChC activation, whereas cPKC inhibition enhanced IKAChC activity in 1-Hz cells. Conclusions: PKC isoforms differentially modulate IKACh, with conventional Ca2+-dependent isoforms inhibiting and novel isoforms enhancing activity. ATR causes a rate-dependent PKC isoform switch, with Ca2+/calpain-dependent downregulation of inhibitory PKC&agr; and membrane translocation of stimulatory PKC&egr;, enhancing IKAChC. These findings provide novel insights into mechanisms underlying IKAChC dysregulation in AF.

Enalapril prevents perpetuation of atrial fibrillation by suppressing atrial fibrosis and over-expression of connexin43 in a canine model of atrial pacing-induced left ventricular dysfunction

Effects of enalapril on a canine model of atrial pacing-induced atrial fibrillation (AF) with rapid ventricular responses were determined. Methods: Four weeks of atrial rapid pacing was performed on twenty-four beagles pretreated with placebo (Group I, n = 14) or enalapril 1 mg/kg (Group II, n = 10). Atrial effective refractory period (ERP), P-wave width, duration of AF, and left ventricular ejection fraction (LVEF) were evaluated every week. AF cycle length was determined by spectral analyses of fibrillation waves. Quantitative analysis of histology was added. Results: After 4 weeks of pacing, P-wave width was longer in Group I than in Group II, and the duration of induced AF was significantly longer in Group I (59.6 ± 66.3 seconds) than in Group II (3.6 ± 3.4 seconds, P < 0.05). AF cycle length was longer in Group I than in Group II despite similar shortening of atrial ERP. Mean ventricular rate during rapid atrial pacing was not different between the two groups. LVEF similarly decreased in both groups. Interstitial fibrosis and expression of connexin43 was greater in Group I than in Group II (interstitial fibrosis, 9.2 ± 8.4 versus 1.9 ± 2.1%, P < 0.05; connexin43, 5.3 ± 2.2 versus 1.1 ± 1.1%, P < 0.05). Conclusions: Enalapril suppressed atrial pacing-induced AF with tachycardia-mediated cardiomyopathy by suppressing interstitial fibrosis, connexin43 over-expression and conduction delay.

Proportion and prognosis of healthy people with coved or saddle-back type ST segment elevation in the right precordial leads during 10 years follow-up

AIMS The aim of this study was to investigate long-term proportion and prognosis of healthy subjects with right precordial ST segment elevation without family history of sudden death. METHODS AND RESULTS We followed up electrocardiograms (ECGs) of 3339 healthy subjects (male/female 2646/693) who underwent periodical medical examination form 1992 to 2001 to determine the relationship between year-to-year changes of ST segment morphology and the risk of fatal arrhythmias. Inclusion criterion was defined as presenting either coved or saddle back type ST segment elevation (>0.2 mV) in the right precordial leads. The cumulative total subjects who showed Brugada-like ECG changes at least once throughout the follow-up period were 69 (male/female 67/2; age 47.9+/-8.9 years, 2.1% of total subjects). During a follow-up period, annual mean proportion of coved or saddle back type ST elevation in the right precordial leads was 1.22+/-0.23% (0.88-1.88%). The morphological pattern of ST segment elevation was saddle-back in 77.3+/-7.9% and coved in 22.7+/-7.9% of subjects. Throughout the follow-up period, 39 subjects (56.5%) showed changes in ST segment elevation pattern. Twenty-nine subjects (42.0%) showed normalization of ST segment elevation at least once. Sixty-nine subjects were followed for a period of one to 10 years (median 4 years, interquartile range 4-8 years). Only one subject with persistent saddle-back type ST elevation had episodes of ventricular fibrillation (VF). CONCLUSIONS The average proportion of healthy subject who had coved or saddle-back type of ST elevation in the right precordial leads without family history of sudden death was 1.22% and the risk of fatal arrhythmias was low (1/393.5 subject-years).

Repolarization dynamics in patients with idiopathic ventricular fibrillation : Pharmacological therapy with bepridil and disopyramide

The electrocardiographic parameters relating occurrence of ventricular fibrillation (VF) episodes in patients with idiopathic VF (IVF) are still unknown. The aim of this study was to clarify efficacy of pharmacological therapy in patients with IVF with respect to repolarization dynamics. The study group consisted of 8 men (age 43.6 ± 9.1 years) with IVF (Brugada type 5 patients, prominent J wave in the inferior leads 3 patients) who had documented spontaneous episodes of VF, 7 of whom had implantable cardioverter defibrillators. The relation between QT and RR interval was analyzed from 24-hour Holter ECG using an automatic analyzing system before and after pharmacological therapy (bepridil 5 and disopyramide 3). From QT-RR linear regression lines, QT intervals were determined at RR intervals of 0.6 second [QT(0.6)], 1.0 second [QT(1.0)], and 1.2 seconds [QT(1.2)]. Pharmacological therapy increased the slope of QT-RR regression line from 0.105 ± 0.020 to 0.144 ± 0.037 (P < 0.05). Accordingly, QT(1.0) and QT(1.2) became longer after drug therapy [QT(1.0), 0.382 ± 0.016 seconds vs 0.414 ± 0.016 seconds (P < 0.01); QT(1.2), 0.403 ± 0.017 seconds vs 0.442 ± 0.021 seconds (P < 0.01)]. However, QT(0.6) did not change after drug administration. Before drug therapy the average episodes of VF were 5.5 ± 5.8 (range 1 to17) during the observation period of 19.3 ± 17.6 months (range 6 to 60 months). After drug therapy, 6 patients had no episode of VF for 24 to 120 months (66.0 ± 38.5 months). Two patients had a single episode of VF for 12- and 96-month follow-ups. Pharmacological therapy decreased the frequency of VF episodes in association with prolongation of QT intervals at slower heart rates. Not only J wave and ST elevation but also shorter QT intervals at slower heart rates may represent an electrophysiological substrate for development of VF episodes in these specific IVF patients.

Vagal activity modulates spontaneous augmentation of J-wave elevation in patients with idiopathic ventricular fibrillation

BACKGROUND Although J-wave elevation in the inferolateral leads could be related to idiopathic ventricular fibrillation (IVF), little is known about the pathophysiologic characteristics of J-wave elevation in patients with IVF. OBJECTIVE This study aimed to determine the relationship between augmentation of J-wave elevation and changes in RR interval or autonomic nervous activities in patients with IVF. METHODS Eight patients with IVF and 22 controls with J-wave elevation (≥0.1 mV) in lead V5 were studied. The J-wave amplitude was automatically measured in lead CM5 of a digital Holter electrocardiogram, and the J-RR relationship was determined. Based on the analysis of heart rate variability, the relationship between the J-wave amplitude and the natural logarithm of high-frequency (HF) components (J-ln HF relationship) or the ratio of low frequency (LF) components to HF components (J-LF/HF relationship) was also determined. RESULTS The J-RR slope (mm/s) was greater in patients with IVF than in controls (3.5 ± 0.7 vs 2.4 ± 0.8; P <.01), as was J-wave amplitude (mm) at an RR interval of 1.2 seconds (2.8 ± 0.9 vs 2.0 ± 0.6; P <.05). The J-wave amplitude was correlated positively with ln HF and negatively with LF/HF, and the slopes of both J-ln HF and J-LF/HF regression lines were greater in patients with IVF than in controls. During an entire 24-hour period, there was no difference between the 2 groups in either HF or LF/HF. Nine of the total 11 episodes (82%) of spontaneous ventricular fibrillation occurred between 18:00 and 6:00. CONCLUSIONS In patients with IVF as compared with control subjects, J-wave elevation was more strongly augmented during bradycardia and was associated with an increase in vagal activity. This could be related to the occurrence of ventricular fibrillation predominantly at night in patients with IVF.

Repolarization abnormality in idiopathic ventricular fibrillation: assessment using 24-hour QT-RR and QaT-RR relationships.

Introduction: We evaluated the characteristics of QT‐RR and QaT (apex of T wave)‐RR relationships in patients with idiopathic ventricular fibrillation (IVF) compared with control subjects. We hypothesized that IVF patients have unique repolarization dynamics related to a reduced fast Na current and a prominent transient outward current.