L-type Voltage-Gated calcium channels partly mediate Mechanotransduction in the intervertebral disc.

Background: Intervertebral disc (IVD) degeneration continues to be a major global health challenge, with strong links to lower back pain, while the pathogenesis of this disease is poorly understood. In cartilage, much more is known about mechanotransduction pathways involving the strain-generated potential (SGP) and function of voltage-gated ion channels (VGICs) in health and disease. This evidence implicates a similar important role for VGICs in IVD matrix turnover. However, the field of VGICs, and to a lesser extent the SGP, remains unexplored in the IVD. Methods: A two-step process was utilized to investigate the role of VGICs in the IVD. First, immunohistochemical staining was used to identify and localize several different VGICs in bovine and human IVDs. Second, a pilot study was conducted on the function of L-type voltage gated calcium channels (VGCCs) by inhibiting these channels with nifedipine (Nf) and measuring calcium influx in monolayer or gene expression from 3D cell-embedded alginate constructs subject to dynamic compression. Results: Several VGICs were identified at the protein level, one of which, Cav2.2, appears to be upregulated with the onset of human IVD degeneration. Inhibiting L-type VGCCs with Nf supplementation led to an altered cell calcium influx in response to osmotic loading as well as downregulation of col 1a, aggrecan and ADAMTS-4 during dynamic compression. Conclusions: This study demonstrates the presence of several VGICs in the IVD, with evidence supporting a role for L-type VGCCs in mechanotransduction. These findings highlight the importance of future detailed studies in this area to fully elucidate IVD mechanotransduction pathways and better inform treatment strategies for IVD degeneration.

Short-Lasting Episodes of Torsade de Pointes in the Chronic Atrioventricular Block Dog Model Have a Focal Mechanism, While Longer-Lasting Episodes Are Maintained by Re-Entry.

OBJECTIVES: This study investigated the arrhythmogenic mechanisms responsible for torsade de pointes (TdP) in the chronic atrioventricular block dog model, known for its high susceptibility for TdP. BACKGROUND: The mechanism of TdP arrhythmias has been under debate for many years. Focal activity as well as re-entry have both been mentioned in the initiation and the perpetuation of TdP. METHODS: In 5 TdP-sensitive chronic atrioventricular block dogs, 56 needle electrodes were evenly distributed transmurally to record 240 unipolar local electrograms simultaneously. Nonterminating (NT) episodes were defibrillated after 10 s. Software was developed to automatically detect activation times and to create 3-dimensional visualizations of the arrhythmia. For each episode of ectopic activity (ranging from 2 beats to NT episodes), a novel methodology was created to construct directed graphs of the wave propagation and detect re-entry loops by using an iterative depth-first-search algorithm. RESULTS: Depending on the TdP definition (number of consecutive ectopic beats), we analyzed 29 to 54 TdP: 29 were longer than 5 beats. In the total group, 9 were NT and 45 were self-terminating. Initiation and termination were always based on focal activity. Re-entry becomes more important in the longer-lasting episodes (>14 beats), whereas in all NT TdP, re-entry was the last active mechanism. During re-entry, excitation fronts were constantly present in the heart, while during focal TdP, there was always a silent interval between 2 consecutive waves (142 ms) during which excitation fronts were absent. Interbeat intervals were significantly smaller for re-entry episodes-220 versus 310 ms in focal. Electrograms recorded in particular areas during NT TdP episodes had significantly smaller amplitude (0.38) than during focal episodes (0.59). CONCLUSIONS: TdP can be driven by focal activity as well as by re-entry depending on the duration of the episode. NT episodes are always maintained by re-entry, which can be identified in local unipolar electrograms by shorter interbeat intervals and smaller deflection amplitude.

ST-Segment Elevation and Fractionated Electrograms in Brugada Syndrome Patients Arise From the Same Structurally Abnormal Subepicardial RVOT Area but Have a Different Mechanism.

BACKGROUND: Brugada syndrome (BrS) is characterized by a typical ECG pattern. We aimed to determine the pathophysiologic basis of the ST-segment in the BrS-ECG with data from various epicardial and endocardial right ventricular activation mapping procedures in 6 BrS patients and in 5 non-BrS controls. METHODS AND RESULTS: In 7 patients (2 BrS and 5 controls) with atrial fibrillation, an epicardial 8×6 electrode grid (interelectrode distance 1 mm) was placed epicardially on the right ventricular outflow tract (RVOT) before video-assisted thoracoscopic surgical pulmonary vein isolation. In 2 other BrS patients, endocardial, epicardial RV (CARTO), and body surface mapping was performed. In 2 additional BrS patients, we performed decremental preexcitation of the RVOT before endocardial RV mapping. During video-assisted thoracoscopic surgical pulmonary vein isolation and CARTO mapping, BrS patients (n=4) showed greater activation delay and more fractionated electrograms in the RVOT region than controls. Ajmaline administration increased the region with fractionated electrograms, as well as ST-segment elevation. Preexcitation of the RVOT (n=2) resulted in ECGs that supported the current-to-load mismatch hypothesis for ST-segment elevation. Body surface mapping showed that the area with ST-segment elevation anatomically correlated with the area of fractionated electrograms and activation delay at the RVOT epicardium. CONCLUSIONS: ST-segment elevation and epicardial fractionation/conduction delay in BrS patients are most likely related to the same structural subepicardial abnormalities, but the mechanism is different. ST-segment elevation may be caused by current-to-load mismatch, whereas fractionated electrograms and conduction delay are expected to be caused by discontinuous conduction in the same area with abnormal myocardium.

Disparate response of high-frequency ganglionic plexus stimulation on sinus node function and atrial propagation in patients with atrial fibrillation.

BACKGROUND: In patients with atrial fibrillation (AF), the autonomic nervous system is supposed to play an role in triggering AF; however, little is known of the effect on atrial conduction characteristics. OBJECTIVE: The purpose of this study was to study the effect of ganglionic plexus (GP) stimulation during sinus rhythm on atrial and pulmonary vein conduction in patients during thoracoscopic surgery for AF METHODS: In 25 patients, the anterior right ganglionic plexus (ARGP) was stimulated (16 Hz, at 1, 2, and 5 mA). Epicardial electrograms were recorded using a 48-electrode map from the right pulmonary vein (RPV) or right atrial (RA). Intra-atrial activation time (IAT), local activation time (LAT), and inhomogeneity of conduction (IIC) were determined. ECG parameters (P-P, P-R interval) were measured. RESULTS: P-P interval was 956 ± 157 ms (range 768-1368 ms), and P-R interval was 203 ± 37 ms (range 136-280 ms). After ARGP stimulation, a short-lasting increase of P-P interval was observed, more prominent at higher output (1 mA = 82 ms, 2 mA = 180 ms, 5 mA = 268 ms, all P <.01 vs baseline). P-R interval remained unchanged. IAT was 34.4 ms (range 5.6-50.3 ms) at the RA and 105.8 ms (range 79.7-163.3 ms) at the RPV. After 1-mA stimulation IAT increased, in patients taking beta-blockers (P = .001), or it decreased, and this change persisted after subsequent stimulation at higher current (1 mA, P = .001; 2 mA, P = .401; 5 mA, P = .593). Similar changes were observed for LAT and IIC. CONCLUSION: ARGP stimulation results in a short-lasting, output-dependent decrease in sinus node frequency due to a parasympathetic response. Stimulation of the ARGP induced a prolonged increase or decrease in conduction characteristics in patients with AF, consistent with a persistent differential parasympathetic and/or sympathetic response.

Health status and fatigue of postpartum anemic women: a prospective cohort study.

OBJECTIVE: The incidence of postpartum anemia is high. Current therapy consists of iron supplementation or blood transfusions, based on the assumption that these treatments improve health status (HS) and reduce fatigue. The aim of this study was to compare HS and fatigue in postpartum women with and without anemia. STUDY DESIGN: This prospective cohort study was performed in The Netherlands between April 2008 and August 2010 and involved 112 anemic (hemoglobin [Hb]<10.5g/dL) and 108 non-anemic (Hb≥10.5g/dL) women. The anemic women received oral iron supplementation. Within 48h and 5 weeks after delivery, HS was measured using the 36 item Short-Form Health Survey (SF-36) and fatigue was measured using the Checklist Individual Strength (CIS). ANOVA for repeated measures was used to compare HS and fatigue scores among groups and across time. RESULTS: After adjustment for confounding variables, there were no differences in any of the HS and fatigue scores. HS and fatigue seem to be more influenced by a complicated delivery than by anemia. HS and fatigue scores significantly improved over time in all women. CONCLUSION: HS and fatigue were not different among women with and without postpartum anemia.

A randomized controlled trial examining the addition of folic acid to iron supplementation in the treatment of postpartum anemia.

OBJECTIVE: To evaluate the efficacy of adding folic acid to oral iron supplementation in postpartum women with anemia. METHODS: A randomized controlled trial was conducted in the Netherlands between April 8, 2008, and August 31, 2010. A total of 112 postpartum women with anemia (hemoglobin <10.5 g/dL) were randomly allocated to receive 600 mg/day ferrous fumarate plus 1mg/day folic acid (FFFA group) or 600/day ferrous fumarate alone (FF group) for 4 weeks. Primary outcome measures were hemoglobin and health status. Secondary outcome measures were fatigue, compliance, and adverse reactions. RESULTS: No between-group differences were observed in hemoglobin and health status after treatment, and no differences were found in fatigue scores. Approximately 75% of all women reported having at least one symptom resulting from ferrous fumarate use. Constipation caused by ferrous fumarate was significantly associated with non-compliance (P=0.014). CONCLUSION: The addition of folic acid to iron supplementation is not beneficial in women with postpartum anemia, as it has no effect on hematologic or health status parameters. CLINICAL TRIAL REGISTRATION: CCMO website NL21797.028.08 and Netherlands Trial Register NTR2232.

Electrocardiographic T wave and its relation with ventricular repolarization along major anatomical axes.

BACKGROUND: The genesis of the electrocardiographic T wave is incompletely understood and subject to controversy. We have correlated the ventricular repolarization sequence with simultaneously recorded T waves. METHODS AND RESULTS: Nine pig hearts were Langendorff-perfused (atrial pacing, cycle length 650 ms). Local activation and repolarization times were derived from unipolar electrograms sampling the ventricular myocardium. Dispersion of repolarization time was determined along 4 anatomic axes: left ventricle (LV)-right ventricle (RV), LV:apico-basal, LV:anterior-posterior, and LV:transmural. The heart was immersed in a fluid-filled bucket containing 61 electrodes to determine Tp (Tpeak in lead of maximum integral), TpTe (Tp to Tend), and TpTe_total (first Tpeak in any lead to last Tend in any lead). Repolarization was nonlinearly distributed in time. RT25 (time at which 25% of sites were repolarized, 288±26 ms) concurred with Tp. TpTe was 38±8 ms, and TpTe_total was 75±9 ms. TpTe_total correlated with dispersion of repolarization time in the entire heart (73±18 ms), but not with dispersion of repolarization times along individual axes (LV-RV, 66±17 ms; LV:apico-basal, 51±18 ms; LV:anterior-posterior, 51±27 ms; mean LV:transmural, 14±7 ms; all n=9). CONCLUSIONS: We provide a correlation between local repolarization and T wave in a pseudo-ECG. Repolarization differences along all anatomic axes contribute to the T wave. TpTe_total represents total dispersion of repolarization. At Tp, ≈25% of ventricular sites have been repolarized.

Complex fractionated electrograms in the right atrial free wall and the superior/posterior wall of the left atrium are affected by activity of the autonomic nervous system.

BACKGROUND: Complex fractionated atrial electrograms (CFAEs) are supposed to be related to structural and electrical remodeling. Animal studies suggest a role of the autonomic nervous system (ANS). However, this has never been studied in humans. OBJECTIVE: The goal of this study was to investigate the influence of ANS on CFAEs in patients with idiopathic atrial fibrillation (AF). METHODS: Thirty-six patients (28 men, 55 ± 9 years) were included before undergoing catheter ablation. In the 24 hours preceding the procedure, 20 patients were in AF (group 1) and 16 were in sinus rhythm (SR, group 2). With 2 decapolar catheters, 1 in the right atrium (RA) and 1 in the left atrium (LA), 20 unipolar electrograms were simultaneously recorded during a 100-second AF-period (in group 2 after induction of AF). After atropine and metoprolol administration, a second 100-second AF-period was recorded 30 minutes later. Five patients of group 2 served as controls and did not receive atropine and metoprolol prior to the second recording. CFAEs were assessed and the prevalence of CFAEs was expressed as percentage of the recording time. RESULTS: The prevalence of CFAEs was greater in group 1 than in group 2 in both RA and LA (P = 0.026, P < 0.001, respectively). Atropine and metoprolol significantly reduced CFAEs in group 1 (P < 0.001) and prevented the time-dependent increase of CFAEs in group 2. CONCLUSION: The prevalence of CFAEs is greater in long-lasting AF episodes. Atropine and metoprolol administration reduces CFAEs in both atria. Thus, CFAEs are at least partly influenced by the ANS.

Drug-induced torsade de pointes arrhythmias in the chronic AV block dog are perpetuated by focal activity.

BACKGROUND: The electrically remodeled canine heart after chronic AV block (CAVB) has a high susceptibility for drug-induced torsade de pointes (TdP) arrhythmias. Although focal mechanisms have been considered for initiation, there is still controversy about whether reentry is the dominant mechanism for perpetuation of TdP. In this animal model with known nonuniform prolongation of repolarization, the mechanism of perpetuation of TdP arrhythmia was explored. METHODS AND RESULTS: Seventeen TdP-sensitive CAVB and 10 sinus rhythm (SR) dogs were studied. In 6 animals, 66 needle electrodes were evenly distributed transmurally to record 240 unipolar local electrograms simultaneously. Activation times and activation recovery intervals were determined before and during ibutilide-induced TdP. In 12 CAVB and 9 SR dogs, left ventricular (LV) and right ventricular (RV) epicardial electrograms were recorded with a 208-point multiterminal grid electrode allowing conduction velocity (CV) and ventricular effective refractory period (VERP) measurements. Biopsy specimens were processed for connexin43 (Cx43) expression and collagen content. Ventricular myocytes were isolated to determine sodium current (I(Na)) density and cell dimensions. Computer simulations were used to assess the effects of changes therein. In CAVB, VERP and ARI were increased, whereas CV was unaltered in LV. Transversal but not longitudinal CV was increased in RV. I(Na) was reduced by 37% in LV but unaltered in RV. LV and RV cell size were increased, but collagen and Cx43 content remained unchanged. Simulations showed increase in CV of RV as a consequence of increased cell size at normal I(Na). Ibutilide increased ARI, ERP, and maximal transmural dispersion of ERP (45 ± 25 to 120 ± 65 ms; P < 0.05). Twenty-eight of 47 episodes of self-terminating TdP (43 ± 72 beats) were analyzed. The majority (> 90%) of beats were focal; reentry was observed only occasionally. CONCLUSIONS: Focal activity is the dominant mechanism involved in perpetuation of ibutilide-induced TdP in CAVB dogs based on detailed 3D mapping. This conclusion is in line with unaltered conduction and documented increase in VERP.

Evaluation of the biological activity of the molluscicidal fraction of Solanum sisymbriifolium against non target organisms.

The evaluation of the biocidal activity of the fruit of Solanum sisymbriifolium involving non target organisms such as aquatic insects, fish and snails lead to the isolation of the steroidal alkaloids, solamargine and ß-solamarine, from the active fractions. The fractions A3 and C, with biological activity against fish, snail and aquatic insect and larvae, are able to affect the good functioning of ecosystem found on alimentary chain. The fraction B seems to be less toxic to fish and aquatic insect and larvae. The fraction B could thus be used as molluscicide in the future.

Mechanism of right precordial ST-segment elevation in structural heart disease: excitation failure by current-to-load mismatch.

BACKGROUND: The Brugada sign has been associated with mutations in SCN5A and with right ventricular structural abnormalities. Their role in the Brugada sign and the associated ventricular arrhythmias is unknown. OBJECTIVE: The purpose of this study was to delineate the role of structural abnormalities and sodium channel dysfunction in the Brugada sign. METHODS: Activation and repolarization characteristics of the explanted heart of a patient with a loss-of-function mutation in SCN5A (G752R) and dilated cardiomyopathy were determined after induction of right-sided ST-segment elevation by ajmaline. In addition, right ventricular structural discontinuities and sodium channel dysfunction were simulated in a computer model encompassing the heart and thorax. RESULTS: In the explanted heart, disappearance of local activation in unipolar electrograms at the basal right ventricular epicardium was followed by monophasic ST-segment elevation. The local origin of this phenomenon was confirmed by coaxial electrograms. Neither early repolarization nor late activation correlated with ST-segment elevation. At sites of local ST-segment elevation, the subepicardium was interspersed with adipose tissue and contained more fibrous tissue than either the left ventricle or control hearts. In computer simulations entailing right ventricular structural discontinuities, reduction of sodium channel conductance or size of the gaps between introduced barriers resulted in subepicardial excitation failure or delayed activation by current-to-load mismatch and in the Brugada sign on the ECG. CONCLUSION: Right ventricular excitation failure and activation delay by current-to-load mismatch in the subepicardium can cause the Brugada sign. Therefore, current-to-load mismatch may underlie the ventricular arrhythmias in patients with the Brugada sign.

Differences in the pattern of ventricular activation in small rodents determined by morphological organization of the cardiac ventricular conduction system.

Ventricular activation of the mouse heart differs significantly compared to activation in larger mammals. Knowledge of structural and functional characteristics of laboratory animals is essential for evaluation of results obtained from experiments. The present study was performed to evaluate whether the different pattern of activation is common to small rodents or unique for mice. Hearts of adult Wistar rats were isolated and Langendorff perfused. After removing the right and left ventricular free wall, extracellular activity of the septum and bundle branches (BB) was determined using a multi-terminal electrode harboring 247 terminals. Immunolabeling on cryosections was performed to assess expression and distribution of the gap junction proteins Connexin40 (Cx40), Cx43, Cx45, contractile (Desmin, alpha-actinin) and intercalated disk-related (N-cadherin, beta-catenin) proteins. Collagen distribution was assessed by Sirius Red staining. Reconstruction of the left and right bundle branch (LBB and RBB) using immuno-labeling revealed that the LBB spreads all over the septal surface. The RBB too is broad, albeit to a lesser extend than LBB. A sheet of connective tissue electrically separates the common bundle and proximal BB from the septal working myocardium. Immunolabeling revealed clear differences between the conduction system and the working myocardium with respect to expression level and distribution of the different proteins analyzed. The morphological organization of the area resulted in an electrical activation pattern of the septum comparable to what is common in larger mammals: earliest activation at the midseptum via the bundle branches. From our data we conclude that the pattern of ventricular activation in the rat heart and the structure of the conduction system fit to data described for larger mammals and differ from the different pattern previously found in mouse heart.

Dominant frequency of atrial fibrillation correlates poorly with atrial fibrillation cycle length.

BACKGROUND: Localized sites of high frequency during atrial fibrillation (AF) are used as target sites to eliminate AF. Spectral analysis is used experimentally to determine these sites. The purpose of this study was to compare dominant frequencies (DF) with AF cycle length (AFCL) of unipolar and bipolar recordings. METHODS AND RESULTS: Left and right atrial endocardial electrograms were recorded during AF in 40 patients with lone AF, using two 20-polar catheters. Mean age was 53+/-9.9 years. Unipolar and bipolar electrograms were recorded simultaneously during 16 seconds at 2 right and 4 left atrial sites. AFCLs and DFs were determined. QRS subtraction was performed in unipolar signals. DFs were compared with mean, median, and mode of AFCLs; 4800 unipolar and 2400 bipolar electrograms were analyzed. Intraclass correlation was poor for all spectral analysis protocols. Best correlation was accomplished with DFs from unipolar electrograms compared with median AFCL (intraclass correlation coefficient, 0.67). A gradient in median AFCL of >25% was detected in 16 of 40 patients. In 13 of 16 patients (81%) with a frequency gradient of >25%, the site with highest frequency was located in the left atrium (posterior left atrium in 8 patients). The site with shortest median AFCL and highest DF corresponded in 25% if unipolar and in 31% if bipolar electrograms were analyzed. CONCLUSIONS: DFs from unipolar and bipolar electrograms recorded during AF correlated poorly with mean, median, and mode AFCL. If a frequency gradient >25% existed, the site with highest DF corresponded to the site of shortest median AFCL in only 25% of patients. Because spectral analysis is being used to identify ablation sites, these data may have important clinical implications.

Combined reduction of intercellular coupling and membrane excitability differentially affects transverse and longitudinal cardiac conduction.

AIMS: Reduced excitability and gap junction expression are commonly found in electrically remodelled diseased hearts, but their contribution to slow conduction and arrhythmias is unclear. In this study, we have investigated the effect of isolated and combined reductions in membrane excitability and intercellular coupling on impulse propagation and arrhythmogeneity in genetically modified mice. METHODS AND RESULTS: Cx43 and Scn5a(1798insD/+) heterozygous (HZ) mice were crossbred to create a mixed offspring: wild-type (WT, n = 15), Cx43 HZ (n = 14), Scn5a(1798insD/+) (Scn5a) HZ (n = 17), and Cx43/Scn5a(1798insD/+) (Cx43/Scn5a) HZ (n = 15) mice. After ECG recording, epicardial activation mapping (208 recording sites) was performed on Langendorff-perfused hearts. Arrhythmia inducibility was tested by one to three premature stimuli and burst pacing. Conduction velocity longitudinal (CV(L)) and transverse (CV(T)) to fibre orientation and dispersion of conduction were determined during S1-S1 pacing (150 ms). Connexin43 (Cx43) and sodium channel Nav1.5 protein expression and myocardial tissue collagen content were determined by immunohistology. Compared with WT animals, P, QRS, and QTc intervals were prolonged in Scn5a HZ and Cx43/Scn5a HZ, but not in Cx43 HZ animals. Scn5a HZ mice showed decreased CV(L) in right ventricle (RV) but not in left ventricle compared with WT. In the RV of Cx43/Scn5a HZ, CV(T) was reduced, but CV(L) was not different from WT. Arrhythmia inducibility was low and not increased in either single- or double-mutant mice. CONCLUSION: Reduction of both electrical coupling and excitability results in normal conduction velocity parallel to fibre orientation but in pronounced conduction slowing transverse to fibre orientation in RV only, although this does not affect arrhythmogeneity.

Effect of anakinra on functional status in patients with active rheumatoid arthritis receiving concomitant therapy with traditional disease modifying antirheumatic drugs: evidence from the OMEGA Trial.

OBJECTIVE: To assess changes in functional status in patients with rheumatoid arthritis (RA) receiving the interleukin-1 receptor antagonist anakinra in addition to a disease modifying antirheumatic drug (DMARD). METHODS: In this large, multicenter, open-label, single-arm study, adult patients with RA receiving methotrexate, sulfasalazine, or hydroxychloroquine for > or = 3 months were given anakinra 100 mg once daily for up to 36 weeks. The primary objective was to evaluate changes from baseline to week 36 in the Health Assessment Questionnaire (HAQ) disability index and subscales. Changes in the 28-joint Disease Activity Score (DAS28), proportion of patients meeting European League Against Rheumatism (EULAR) response criteria, and the safety of each combination regimen were also assessed. RESULTS: A total of 1207 patients were enrolled, received > or = 1 dose of anakinra, and were included in the efficacy and safety analyses. A statistically significant change in the HAQ disability index was observed (p = 0.0001); no significant differences were seen among the 3 DMARD groups. A clinically meaningful improvement in HAQ (> 0.22) was observed in 51% of patients. Mean improvement in DAS28 was 1.5 (p < 0.0001), and 64% of patients achieved a good or moderate EULAR response score. Injection site reaction was the most frequently (62%) reported adverse event. The incidence of infections (24%), most commonly respiratory infection, was similar across treatment groups. No notable changes were observed in laboratory findings and vital signs. CONCLUSION: These findings indicate that anakinra 100 mg/day in combination with DMARD therapy safely improved functional status in patients with active RA.

Slow and discontinuous conduction conspire in Brugada syndrome: a right ventricular mapping and stimulation study.

BACKGROUND: Brugada syndrome (BrS) is associated with lethal arrhythmias, which are linked to specific ST-segment changes (type-1 BrS-ECG) and the right ventricle (RV). The pathophysiological basis of the arrhythmias and type-1 BrS-ECG is unresolved. We studied the electrophysiological characteristics of the RV endocardium in BrS. METHODS AND RESULTS: RV endocardial electroanatomical mapping and stimulation studies were performed in controls (n=12) and BrS patients with a type-1 (BrS-1, n=10) or type-2 BrS-ECG (BrS-2, n=12) during the studies. BrS-1 patients had prominent impairment of RV endocardial impulse propagation when compared with controls, as represented by: (1) prolonged activation-duration during sinus rhythm (86+/-4 versus 65+/-3 ms), (2) increased electrogram fractionation (1.36+/-0.04 versus 1.15+/-0.01 deflections per electrogram), (3) longer electrogram duration (83+/-3 versus 63+/-2 ms), (4) activation delays on premature stimulation (longitudinal: 160+/-26 versus 86+/-9 ms; transversal: 112+/-5 versus 58+/-6 ms), and (5) abnormal transversal conduction velocity restitution (42+/-8 versus 18+/-2 ms increase in delay at shortest coupling intervals). Wider and more fractionated electrograms were also found in BrS-2 patients. Repolarization was not different between groups. CONCLUSIONS: BrS-1 and BrS-2 patients are characterized by wide and fractionated electrograms at the RV endocardium. BrS-1 patients display additional conduction slowing during sinus rhythm and premature stimulation along with abnormal transversal conduction velocity restitution. These patients may thus exhibit a substrate for slow and discontinuous conduction caused by abnormal active membrane processes and electric coupling. Our findings support the emerging notion that BrS is not solely attributable to abnormal electrophysiological properties but requires the conspiring effects of conduction slowing and tissue discontinuities.

Monophasic action potentials and activation recovery intervals as measures of ventricular action potential duration: experimental evidence to resolve some controversies.

BACKGROUND: Activation recovery intervals (ARIs) and monophasic action potential (MAP) duration are used as measures of action potential duration in beating hearts. However, controversies exist concerning the correct way to record MAPs or calculate ARIs. We have addressed these issues experimentally. OBJECTIVES: To experimentally address the controversies concerning the correct way to record MAPs or calculate ARIs. METHODS: Left ventricular local electrograms were recorded in isolated pig hearts with an exploring electrode grid, with a KCl reference electrode on the left ventricular myocardium, the aortic root, or the left atrium. Local activation was determined from calculated Laplacian electrograms. RESULTS: With the KCl electrode on the aortic root, local electrograms represented local activation. However, with the KCl electrode on the myocardium remote from the exploring electrode, a combined electrogram emerged consisting of local activation recorded from the grid and remote activation recorded from the reference electrode. The remote, inverted monophasic component did not show propagation and did not correlate with the Laplacian complex. When the KCl electrode was placed on the atrium during AV block, remote atrial monophasic components were completely dissociated from local, ventricular deflections. At left ventricular sites with a positive T wave, the Laplacian signal showed that the end of the T wave was caused by remote repolarization. During cooling-induced regional action potential prolongation, the T wave became negative, whereby the positive flank of the T wave remained correlated with repolarization (recorded with a MAP at the same site). CONCLUSIONS: MAPs are recorded from the depolarizing electrode. In both negative and positive T waves, the moment of maximum dV/dt corresponds to local repolarization.

Antimony-induced cardiomyopathy in guinea-pig and protection by L-carnitine.

Antimony (Sb) is the mainstay for the treatment of Leishmaniasis. It has serious, often lethal, cardiovascular side effects. The objective of this study was to examine the effects of Sb treatment upon the electrocardiogram (ECG), myocyte contractility (assessed by monitoring sarcomere length during field stimulation), whole-cell action potential (AP) and calcium current (I(Ca)) of the guinea-pig and to evaluate L-carnitine as a cardioprotective agent. Guinea-pigs received daily injections of either saline, Sb(V), Sb(III), L-carnitine or L-carnitine with Sb(III). Eight lead ECGs were recorded under halothane anaesthesia every 4 days. At the end of each treatment regime, animals were killed and ventricular myocytes were enzymatically isolated. Treatment with Sb(V) for 26 days prolonged the QT interval of the ECG. Treatment with Sb(III) was lethal within 2 days for approximately 50% of the animals. The survivors showed ECG alterations similar to those described in man: T wave flattening and/or inversion, depression of the ST segment, and elongation of RR and QT intervals. Their ventricular myocytes showed impaired contraction responses to changes in stimulus frequency, elongated AP and reduced I(Ca). Combined treatment with L-carnitine and Sb(III) delayed mortality. Prior treatment with L-carnitine followed by combined treatment with L-carnitine and Sb(III) reduced mortality to <10% over 12 days and these animals showed normal ECG. Their myocytes showed normal contractility and AP. It is concluded that L-carnitine has a preventive cardioprotective role against antimony-induced cardiomyopathy. The mechanism of action of L-carnitine may be to counter oxidative stress caused by Sb(III).

On the atrial response to focal discharges in man.

INTRODUCTION: Triggers and vulnerability are key factors for the occurrence of atrial fibrillation (AF). The aim of this study was to assess spatial dispersion of atrial refractoriness and vulnerability in response to both focal discharges as well as programmed electrical stimulation in patients undergoing ablation of atrial arrhythmogenic foci. METHODS AND RESULTS: Twenty-nine patients were studied, and 12 right atrial unipolar electrograms were recorded. Inducibility of AF was assessed by a pacing protocol that started with one extrastimulus, followed by more aggressive pacing until AF was obtained. Mean fibrillatory intervals were used to assess the local refractoriness of each recording site. Spatial dispersion of refractoriness was calculated as the coefficient of dispersion (CD value: standard deviation of the mean of all local mean fibrillatory intervals as a percentage of the overall mean fibrillatory interval). Based on our previous study, a CD value 3.0 was considered enhanced spatial dispersion of refractoriness. Fifteen of 29 patients had normal dispersion of refractoriness (mean CD value 1.65 +/- 0.43), and AF was inducible with burst pacing only. These patients had focal discharges causing rapid atrial tachycardia with a focal activation pattern. Activation mapping of focal activity was possible in 14 of 15 patients. Focal triggering of AF occurred in only 1 of 15 patients. Fourteen of 29 patients had enhanced dispersion (mean CD value 4.2 +/- 0.72). AF was inducible with a single extrastimulus in 11 of 14 patients (P < 0.001). Focal triggering of AF occurred in all 14 patients. CONCLUSION: Spatial dispersion of atrial refractoriness determines whether focal atrial discharges trigger AF with disorganized activity or, alternatively, only rapid atrial tachycardia.