Predictors of successful complex catheter ablation for persistent atrial fibrillation despite failure of targeted procedural arrhythmia termination.

INTRODUCTION: Procedural atrial fibrillation (AF) termination is considered as a predictor of long-term success after catheter ablation for persistent AF (persAF). However, some patients remain free of arrhythmia recurrences despite failure to achieve AF termination. The objective of this study was to assess long-term outcome and prognostic factors in patients undergoing complex ablation without procedural AF termination. METHODS AND RESULTS: This study comprised 419 patients (63.8 ± 10.2 years, 63.4% male) undergoing complex ablation for persAF. Patients without procedural AF termination (n = 137, 64.2 ± 9.7 years, 63.5% male) were categorized into patients who remained in sinus rhythm (SR) in long-term outcome (SR-group) and patients with recurrence of AF or atrial tachycardia (AT) (AR-group). During a follow-up (FU) of 19.6 ± 14.6 months, the SR-group consisted of 65 (47.5%) and the AR-group of 69 (50.4%) patients. Three patients (2.2%) were lost to FU. Left atrial appendage (LAA) flow velocity and left atrium volume index (LAVI) could be identified as predictors for long-term success. LAA flow velocity and baseline AF cycle length (AFCL) were significantly associated with the type of arrhythmia recurrence (AF vs AT), ie, higher values of both are predictive for AT rather than AF recurrences. Patients with a LAVI < 34.4 mL/m² and significant AFCL increase during the ablation procedure had rather AT than AF recurrences. CONCLUSION: Patients with an arrhythmia-free outcome despite failure of procedural AF termination during complex ablation for persAF are characterized by specific morphological and functional properties that are easy to obtain.

Crucial role for Nox2 and sleep deprivation in aircraft noise-induced vascular and cerebral oxidative stress, inflammation, and gene regulation.

Aims: Aircraft noise causes endothelial dysfunction, oxidative stress, and inflammation. Transportation noise increases the incidence of coronary artery disease, hypertension, and stroke. The underlying mechanisms are not well understood. Herein, we investigated effects of phagocyte-type NADPH oxidase (Nox2) knockout and different noise protocols (around-the-clock, sleep/awake phase noise) on vascular and cerebral complications in mice. Methods and results: C57BL/6j and Nox2-/- (gp91phox-/-) mice were exposed to aircraft noise (maximum sound level of 85 dB(A), average sound pressure level of 72 dB(A)) around-the-clock or during sleep/awake phases for 1, 2, and 4 days. Adverse effects of around-the-clock noise on the vasculature and brain were mostly prevented by Nox2 deficiency. Around-the-clock aircraft noise of the mice caused the most pronounced vascular effects and dysregulation of Foxo3/circadian clock as revealed by next generation sequencing (NGS), suggesting impaired sleep quality in exposed mice. Accordingly, sleep but not awake phase noise caused increased blood pressure, endothelial dysfunction, increased markers of vascular/systemic oxidative stress, and inflammation. Noise also caused cerebral oxidative stress and inflammation, endothelial and neuronal nitric oxide synthase (e/nNOS) uncoupling, nNOS mRNA and protein down-regulation, and Nox2 activation. NGS revealed similarities in adverse gene regulation between around-the-clock and sleep phase noise. In patients with established coronary artery disease, night-time aircraft noise increased oxidative stress, and inflammation biomarkers in serum. Conclusion: Aircraft noise increases vascular and cerebral oxidative stress via Nox2. Sleep deprivation and/or fragmentation caused by noise triggers vascular dysfunction. Thus, preventive measures that reduce night-time aircraft noise are warranted.

Cardiac arrhythmias in patients with Danon disease.

AIMS: Different cardiac arrhythmias have been suggested to be associated with Danon disease, e.g. Wolff-Parkinson-White syndrome. However, a systematic electrophysiological investigation of patients with Danon disease is lacking thus far. METHODS AND RESULTS: Seven patients with Danon disease (4 males, 35.8 ± 10.8 years; 3 females, 51.3 ± 19.9 years) from 3 different families were studied. In all patients, the presence of Danon disease was confirmed by western blot of biopsy material or genetic testing. The patients were characterized by 12-lead electrocardiogram (ECG), Holter ECG, echocardiography, and serial implantable cardioverter defibrillator (ICD) interrogations (in ICD recipients). All male patients underwent electrophysiological investigation (EP study). Asymptomatic ventricular tachyarrhythmias were documented in six of the seven patients. Moreover, 5 of the 7 patients suffered from atrial fibrillation (AF), with 1 of them experiencing thromboembolic stroke at the age of 30 years. In male patients, the initial QRS complex was characterized by a slurring upstroke and shortened PQ interval mimicking ventricular pre-excitation. One male patient showed initial QRS complex slurring with prolonged PR interval. However, the presence of an accessory pathway was excluded by an EP study in all patients. In female patients, initial QRS complex slurring was significantly less distinct. In four patients, ICD implantation was performed for primary prevention of sudden cardiac death. However, sustained ventricular arrhythmias were not documented in any of the patients. CONCLUSIONS: The present study indicates that the distinct surface ECG pattern in Danon disease is not associated with ventricular pre-excitation. Atrial fibrillation is frequently observed in these patients and may be associated with thromboembolic events in the young, while sustained ventricular arrhythmias occur less frequently than previously reported.

Primary Persistent Atrial Fibrillation: A Distinct Arrhythmia Subentity of an Ablation Population.

INTRODUCTION: Persistent atrial fibrillation (persAF) can occur either as a sustained arrhythmia that has progressed from initially paroxysmal AF or as primary persAF without a history of any spontaneously terminated episode. There is a paucity of data differentiating between the 2 different persAF entities. Thus, we prospectively evaluated baseline characteristics, electrophysiological features, and ablation outcome in these 2 patient cohorts. METHODS AND RESULTS: A total number of 154 consecutive persAF patients (63 ± 10 years, f = 42, longstanding persAF = 60) were characterized in terms of having primary persAF (P-persAF group) or persAF that secondarily progressed from paroxysmal AF (S-persAF group). All patients underwent de novo catheter ablation using the stepwise approach. PersAF entities were characterized by detailed patient history, sequential Holter monitoring, and reports of documented modes of AF conversion, respectively. The P-persAF group had a higher number of young patients (<50 years), a shorter AF history, and a higher number of congestive heart failure. The HATCH score did not differ between the groups. Procedural AF termination rate was significantly higher in S-persAF than in P-persAF patients (n = 55 [81%] vs. n = 58 [68%], P = 0.043). At 1-year follow-up, the arrhythmia-free survival after a single procedure was significantly lower in patients with P-persAF (26% vs. 43%, P = 0.016). Categorization to P-persAF was the strongest independent predictor of arrhythmia recurrence. CONCLUSIONS: P-persAF seems to be a specific arrhythmia entity that is associated with a lower AF-termination rate and a worse outcome after catheter ablation as compared to S-persAF.

The Incidence of Audible Steam Pops Is Increased and Unpredictable With the ThermoCool® Surround Flow Catheter During Left Atrial Catheter Ablation: A Prospective Observational Study.

INTRODUCTION: Open irrigated radiofrequency (RF) ablation catheters with a porous tip (56 holes, TC-SF) permit delivering RF energy in a temperature-controlled mode without temperature rise. This prospective observational study investigated the association of different catheter parameters on the occurrence of audible steam pops during left atrial (LA) ablation. METHODS AND RESULTS: A total of 226 patients underwent TC-SF catheter ablation for atrial fibrillation. RF power delivery, impedance and catheter tip temperature were continually recorded throughout the ablation. Pulmonary vein isolation was performed with a maximum of 27 W and LA electrogram-guided or linear ablation with a maximum of 30 W. A total of 59 audible steam pops occurred, 2 of them resulting in pericardial tamponade. In the initial 89 patients, with an irrigation flow rate of 10 mL/min, 18 steam pops with one tamponade occurred in 12 (14%) patients. Subsequently, the irrigation flow rate was increased to 20 mL/min in the following 137 patients, resulting in the occurrence of 41 steam pops including one case of tamponade in a total of 30 (22%) patients. The maximal power was significantly higher in RF applications associated with a pop than those that did not. In only 12 (20%) steam pops, a significant impedance change occurred immediately before pop occurrence (4 [7%] impedance rise >10 ohm, 8 [13%] impedance drop >15 ohm). CONCLUSIONS: The TC-SF catheter does not provide sufficient feedback from the ablated tissue to prevent steam popping.

Reduction of ICD shock burden by eliminating back-up pacing induced ventricular tachyarrhythmias.

INTRODUCTION: Implantable cardioverter defibrillators (ICD) may have the capacity to provoke or worsen ventricular tachyarrhythmias (VT). It has been reported that ICD shocks by itself can increase mortality. This study aimed to determine the role of back-up pacing-induced VT (PIT) in the overall ICD shock burden by avoiding pause-related ventricular back-up pacing. METHODS AND RESULTS: A population of 550 single-chamber ICD patients was studied. Of them, 17 (3%, 69 ± 16 years, 14 male) patients had documented episodes of PIT. A total of 431 VT episodes were documented including 89 (21%) due to PIT. In 3 patients, VT events were exclusively PITs. After ≥2 documented PITs, the pacing output for VVI pacing was set to a subthreshold level resulting in noncapturable ventricular back-up pacing. All other device parameters remained unchanged to prove a potential proarrhythmic effect of pause related back-up pacing. During a follow-up of 99 ± 39 months after reducing the pacing output to a subthreshold level, no further episodes of PIT were observed (P < 0.001). Moreover, with the prevention of PITs, the ICD shock burden decreased significantly (pre: 150 vs. post: 18, P < 0.001). However, a single event of pause-induced VT occurred due to missing back-up pacing. CONCLUSIONS: PIT is a frequent mechanism of VTs in ICD patients resulting in a substantially increased shock burden. Elimination of pause-related back-up pacing by subthreshold pacing output effectively abolishes PIT and thus significantly reduces ICD shock burden.

Automated three-dimensional activation versus conventional mapping for catheter ablation of atrial tachycardia - A prospective randomized trial.

Background: The automated NavX Ensite Precision latency-map (LM) algorithm aims to identify atrial tachycardia (AT) mechanisms. However, data on a direct comparison of this algorithm with conventional mapping are scarce. Methods: Patients scheduled for AT ablation were randomized to mapping with the LM- algorithm (LM group) or to conventional mapping (conventional only group: ConvO), using entrainment and local activation mapping techniques. Several outcomes were exploratively analyzed. Primary endpoint was intraprocedural AT Termination. If AT termination with only automated 3D-Mapping failed, additional conventional methods were applied (conversion). Results: A total of 63 patients (mean 67 years, 34 % female) were enrolled. In the LM group (n = 31), the correct AT mechanism was identified in 14 patients (45 %) using the algorithm alone compared to 30 patients (94 %) with conventional methods. Time to termination of the first AT was not different between groups (LM group 34 ± 20 vs. ConvO 43.1 ± 28.3 min; p = 0.2). However, when AT termination did not occur with LM algorithm, time to termination prolonged significantly (65 ± 35 min; p = 0.01). After applying conventional methods (conversion), procedural termination rates did not differ between LM group (90 %) vs. ConvO (94 %) (p = 0.3). During a follow-up time of 20 ± 9 months, no differences were observed in clinical outcomes. Conclusion: In this small prospective, randomized study, the use of the LM algorithm alone may lead to AT termination, but less accurate than conventional methods.

Durable pulmonary vein isolation but not complex substrate ablation determines the type of arrhythmia recurrence after persistent atrial fibrillation ablation.

BACKGROUND: Complex ablation for persistent atrial fibrillation (AF) aims to modify the arrhythmogenic substrates to become incapable to perpetuate the arrhythmia. Ablation-associated determinants of atrial tachycardia (AT) rather than AF recurrences are unknown. The aim of the study was to evaluate the association between the type of arrhythmia recurrence and electrophysiological findings during redo procedures. METHODS: A total number of 384 consecutive patients with persistent AF underwent complex ablation consisting of PV isolation (PVI), biatrial electrogram-guided ablation, and linear ablation with the desired procedural endpoint of AF termination. Electrophysiological findings during redo procedures and its relation to AR type are the subject of this study. RESULTS: Overall, 177 (46%) patients underwent a second procedure. Patients with AT recurrences had significantly more often persistent PVI (47 vs. 25%; P = 0.002). Moreover, a higher number of recovered PVs were associated with AF recurrence (3 PVs recovered, AF = 16.1% vs. AT = 5.2%; P = 0.02; 4 PVs recovered, AF = 18.5% vs. AT = 6.3%; P = 0.01), regardless of the extent of substrate ablation during the first procedure. CONCLUSIONS: Durable PV isolation but not the extent of atrial substrate ablation determines the type of arrhythmia recurrence. Thus, the PVs may represent dominant perpetuators (and not only triggers) of persistent AF even in the presence of a significantly modified atrial substrate.

In vitro comparison of platinum-iridium and gold tip electrodes: lesion depth in 4 mm, 8 mm, and irrigated-tip radiofrequency ablation catheters.

AIMS: We compared a newly developed irrigated gold tip electrode ablation catheter and a gold tip 4 and 8 mm catheter with the corresponding platinum-iridium (Pt) tip catheters in an in vitro setting. METHODS AND RESULTS: In a flow chamber simulating physiological flow conditions, radiofrequency catheter ablation was performed on tissue samples of porcine endomyocardium and liver. Lesion depth, energy and temperature delivery, and popping frequency were determined. Two hundred and fifty-three ablations were conducted. Four and eight millimetre, gold tip electrode catheters produced significantly deeper lesions compared with the Pt tip electrode (liver 4 mm: 4.67 +/- 1.7 vs. 2.9 +/- 1.0 mm, P < 0.0001; endomyocardium 4 mm: 3.88 +/- 1.1 vs. 2.81 +/- 0.7 mm, P < 0.001; liver 8 mm: 3.98 +/- 1.0 vs. 2.03 +/- 1.1 mm, P < 0.001; endomyocardium 8 mm: 4.00 +/- 0.9 vs. 3.39 +/- 0.8 mm, P < 0.001) and correlated with the amount of energy delivery. Popping frequency was significantly higher in gold tip electrodes. In irrigated tip electrodes, there was no difference in the lesion depth comparing gold with Pt (liver: 5.18 +/- 0.7 vs. 5.01 +/- 0.7 mm, P = ns; endomyocardium: 4.89 +/- 0.7 vs. 4.78 +/- 0.8 mm, P = ns). There was a trend towards less popping in the gold tip electrode. CONCLUSION: Both 4 and 8 mm not-irrigated gold tip catheters produced deeper lesions than the corresponding Pt tip catheter. In irrigated tip catheters, gold and Pt tip material did not show differences in the lesion depth.

Heme oxygenase-1: a novel key player in the development of tolerance in response to organic nitrates.

OBJECTIVE: Nitrate tolerance is likely attributable to an increased production of reactive oxygen species (ROS) leading to an inhibition of the mitochondrial aldehyde dehydrogenase (ALDH-2), representing the nitroglycerin (GTN) and pentaerythrityl tetranitrate (PETN) bioactivating enzyme, and to impaired nitric oxide bioactivity and signaling. We tested whether differences in their capacity to induce heme oxygenase-1 (HO-1) might explain why PETN and not GTN therapy is devoid of nitrate and cross-tolerance. METHODS AND RESULTS: Wistar rats were treated with PETN or GTN (10.5 or 6.6 microg/kg/min for 4 days). In contrast to GTN, PETN did not induce nitrate tolerance or cross-tolerance as assessed by isometric tension recordings in isolated aortic rings. Vascular protein and mRNA expression of HO-1 and ferritin were increased in response to PETN but not GTN. In contrast to GTN therapy, NO signaling, ROS formation, and the activity of ALDH-2 (as assessed by an high-performance liquid chromatography-based method) were not significantly influenced by PETN. Inhibition of HO-1 expression by apigenin induced "tolerance" to PETN whereas HO-1 gene induction by hemin prevented tolerance in GTN treated rats. CONCLUSIONS: HO-1 expression and activity appear to play a key role in the development of nitrate tolerance and might represent an intrinsic antioxidative mechanism of therapeutic interest.

Does nitric oxide mediate the vasodilator activity of nitroglycerin?

Nitroglycerin (glyceryl trinitrate, GTN) relaxes blood vessels primarily via activation of the soluble guanylyl cyclase (sGC)/cGMP/cGMP-dependent protein kinase (cGK-I) pathway. Although the precise mechanism of sGC activation by GTN in the vascular wall is unknown, the mediatory role of nitric oxide (NO) has been postulated. We tested the GTN/NO hypothesis in different types of isolated rat and rabbit blood vessels using two novel approaches: (1) EPR spin trapping using colloid Fe(DETC)2 and (2) analysis of cGK-I-dependent phosphorylation of the vasodilator-stimulated phosphoprotein at Ser239 (P-VASP). For comparison, another organic nitrate, isosorbide dinitrate (ISDN), and endothelium-dependent vasodilator, calcium ionophore A23187, were tested. We found a marked discrepancy between GTN's strong vasoactivity (vasodilation and augmentation of P-VASP) and its poor NO donor properties. In aortas precontracted with phenylephrine, GTN, ISDN, and A23187 induced nearly full relaxations (>80%) and doubling of vascular P-VASP content at concentrations of 100 nmol/L, 100 micromol/L, and 1 micromol/L, respectively. GTN applied in vasorelaxant concentrations (10 to 1000 nmol/L) did not significantly increase the basal vascular NO production, in contrast to ISDN and A23187. The absence of GTN-derived NO was confirmed in rabbit vena cava and renal artery. A significant increase in vascular NO formation was observed only at suprapharmacological GTN concentrations (>10 micromol/L). The concentration dependency of NO formation from GTN was comparable to that of ISDN, although the latter exhibits 100-folds lower vasorelaxant potency. We conclude that GTN activates the sGC/cGMP/cGK-I pathway and induces vasorelaxation without intermediacy of the free radical NO. The full text of this article is available online at http://www.circresaha.org.

Effects of angiotensin II infusion on the expression and function of NAD(P)H oxidase and components of nitric oxide/cGMP signaling.

Angiotensin II infusion causes endothelial dysfunction by increasing NAD(P)H oxidase-mediated vascular superoxide production. However, it remains to be elucidated how in vivo angiotensin II treatment may alter the expression of the gp91(phox) isoforms and the endothelial nitric oxide synthase (NOS III) and subsequent signaling events and whether, in addition to the NAD(P)H oxidase, NOS III contributes to vascular superoxide formation. We therefore studied the influence of in vivo angiotensin II treatment (7 days) in rats on endothelial function and on the expression of the NAD(P)H oxidase subunits p22(phox), nox1, nox4, and gp91(phox) and NOS III. Further analysis included the expression of NO-downstream targets, the soluble guanylyl cyclase (sGC), the cGMP-dependent protein kinase I (cGK-I), and the expression and phosphorylation of the vasodilator-stimulated phosphoprotein (VASP) at Ser239 (P-VASP). Angiotensin II caused endothelial dysfunction and increased vascular superoxide. Likewise, we found an increase in vascular protein kinase C (PKC) activity, in the expression of nox1 (6- to 7-fold), gp91(phox) (3-fold), p22(phox) (3-fold), NOS III mRNA, and protein. NOS-inhibition with N(G)-nitro-L-arginine decreased superoxide in vessels from angiotensin II-treated animals, compatible with NOS-uncoupling. Vascular NO assessed with electron paramagnetic resonance was markedly reduced. Likewise, a decrease in sGC-expression and P-VASP levels was found. In vivo PKC-inhibition with chelerythrine reduced angiotensin II-induced superoxide production and markedly inhibited upregulation of NAD(P)H oxidase subunits. We therefore conclude that angiotensin II-induced increases in the activity and the expression of NAD(P)H oxidase are at least in part PKC-dependent. NADPH oxidase-induced superoxide production may trigger NOS III uncoupling, leading to impaired NO/cGMP signaling and to endothelial dysfunction in this animal model. The full text of this article is available at http://www.circresaha.org.

Mechanisms of increased vascular superoxide production in an experimental model of idiopathic dilated cardiomyopathy.

OBJECTIVE: In the present study, we sought to identify mechanisms underlying increased oxidative stress in vascular tissue in an experimental animal model of chronic congestive heart failure (CHF). METHODS AND RESULTS: Superoxide and nitric oxide (NO) was measured in vessels from cardiomyopathic hamsters (CHF hamsters) and golden Syrian hamsters. We also determined expression of endothelial nitric oxide synthase (NOSIII), the soluble guanylyl cyclase, the cGMP-dependent kinase, and the NADPH oxidase. To analyze the contribution of the renin-angiotensin system to oxidative stress, CHF hamsters were treated with the angiotensin-converting enzyme inhibitor captopril for 200 days (120 mg . kg(-1) . d(-1)). CHF led to increased superoxide production by NOSIII and the NADPH oxidase. Decreased NO production in CHF was associated with a decrease in the expression of NOSIII and an inhibition of NO downstream signaling in the aorta. NOSIII expression was increased within the left ventricle. Captopril treatment normalized NOSIII expression in vessels and the myocardium, reduced superoxide levels, and prevented NOSIII uncoupling. Accordingly, endothelial function, NO production, and downstream signaling were improved in CHF vessels. CONCLUSIONS: Oxidative stress in CHF is mediated by NADPH oxidase and an uncoupled NOSIII secondary to an activation of the renin-angiotensin system leading to impaired NO downstream signaling.

Mitochondrial oxidative stress and nitrate tolerance--comparison of nitroglycerin and pentaerithrityl tetranitrate in Mn-SOD+/- mice.

BACKGROUND: Chronic therapy with nitroglycerin (GTN) results in a rapid development of nitrate tolerance which is associated with an increased production of reactive oxygen species (ROS). According to recent studies, mitochondrial ROS formation and oxidative inactivation of the organic nitrate bioactivating enzyme mitochondrial aldehyde dehydrogenase (ALDH-2) play an important role for the development of nitrate and cross-tolerance. METHODS: Tolerance was induced by infusion of wild type (WT) and heterozygous manganese superoxide dismutase mice (Mn-SOD+/-) with ethanolic solution of GTN (12.5 mug/min/kg for 4 d). For comparison, the tolerance-free pentaerithrityl tetranitrate (PETN, 17.5 mug/min/kg for 4 d) was infused in DMSO. Vascular reactivity was measured by isometric tension studies of isolated aortic rings. ROS formation and aldehyde dehydrogenase (ALDH-2) activity was measured in isolated heart mitochondria. RESULTS: Chronic GTN infusion lead to impaired vascular responses to GTN and acetylcholine (ACh), increased the ROS formation in mitochondria and decreased ALDH-2 activity in Mn-SOD+/- mice. In contrast, PETN infusion did not increase mitochondrial ROS formation, did not decrease ALDH-2 activity and accordingly did not lead to tolerance and cross-tolerance in Mn-SOD+/- mice. PETN but not GTN increased heme oxygenase-1 mRNA in EA.hy 926 cells and bilirubin efficiently scavenged GTN-derived ROS. CONCLUSION: Chronic GTN infusion stimulates mitochondrial ROS production which is an important mechanism leading to tolerance and cross-tolerance. The tetranitrate PETN is devoid of mitochondrial oxidative stress induction and according to the present animal study as well as numerous previous clinical studies can be used without limitations due to tolerance and cross-tolerance.

Adverse effects of nitroglycerin treatment on endothelial function, vascular nitrotyrosine levels and cGMP-dependent protein kinase activity in hyperlipidemic Watanabe rabbits.

OBJECTIVE: With the present studies we sought to determine how treatment with nitroglycerin (NTG) affects endothelial function, oxidative stress and nitric oxide (NO)-downstream signaling in Watanabe heritable hyperlipidemic rabbits (WHHL). BACKGROUND: In vitro experiments have demonstrated potent antiatherosclerotic effects of NO suggesting that treatment with NO-donors such as NTG could compensate for the diminished availability of endothelial NO. Nitric oxide may, however, not only be scavenged by reaction with endothelium-derived superoxide but also form the potent oxidant and inhibitor of vascular function, peroxynitrite (ONOO(-)). METHODS: Watanabe heritable hyperlipidemic rabbits were treated for three days with NTG patches. Normolipidemic New Zealand White rabbits (NZWR) served as controls. Endothelial function was assessed ex vivo with organ chamber experiments and vascular superoxide was quantified using lucigenin (5 and 250 microM) and CLA-enhanced chemiluminescence. Vascular ONOO(-) formation was determined using nitrotyrosine antibodies. The activity of the cGMP-dependent kinase (cGK-I) was assessed by determining the phosphorylation of vasodilator-stimulated phosphoprotein VASP (P-VASP). RESULTS: Nitroglycerin treatment caused endothelial dysfunction in NZWR and WHHL, associated with an increase in superoxide and ONOO(-) production and a substantial drop in cGK-I activity. In vivo NTG-treatment decreased lipophilic antioxidants (alpha- and beta-carotene) in NZWR and WHHL. Treatment of NZWR with NTG also decreased plasma extracellular superoxide dismutase (EC-SOD)-activity. CONCLUSIONS: Nitroglycerin treatment of WHHL with exogenous NO worsens rather than improves endothelial dysfunction secondary to increased formation of superoxide and/or peroxynitrite leading to decreased cGK-I activity. The decrease in plasma levels of alpha- and beta-carotene may be at least in part due to a decrease in EC-SOD activity.

Role for peroxynitrite in the inhibition of prostacyclin synthase in nitrate tolerance.

OBJECTIVES: We tested whether in vivo nitroglycerin (NTG) treatment causes tyrosine nitration of prostacyclin synthase (PGI(2)-S), one of the nitration targets of peroxynitrite, and whether this may contribute to nitrate tolerance. BACKGROUND: Long-term NTG therapy causes tolerance secondary to increased vasoconstrictor sensitivity and increased vascular formation of reactive oxygen species. Because NTG releases nitric oxide (NO), NTG-induced stimulation of superoxide production should increase vascular nitrotyrosine levels, compatible with increased formation of peroxynitrite, the reaction product from NO and superoxide. METHODS: New Zealand White rabbits and Wistar rats were treated with NTG (0.4 mg/h for 3 days). Tolerance was assessed with isometric tension studies. Vascular peroxynitrite levels were quantified with luminol-derived chemiluminescence (LDCL) and peroxynitrite scavengers, such as uric acid and ebselen. As a surrogate parameter for the assessment of the activity of cyclic guanosine monophosphate-dependent kinase-I (cGK-I; the final signaling pathway for NO), the phosphorylation of the vasodilator-stimulated phosphoprotein (P-VASP) at serine 239 was analyzed. RESULTS: Nitroglycerin treatment increased LDCL, and the inhibitory effect of uric acid and ebselen on LDCL was augmented in tolerant rings. Immunoprecipitation of 3-nitrotyrosine-containing proteins and immunohistochemistry analysis identified PGI(2)-S as a tyrosine-nitrated protein. Accordingly, conversion of ((14)C)-PGH(2) into 6-keto-PGF(1 alpha) (=PGI(2)-S activity) was strongly inhibited. In vitro incubation of tolerant rings with ebselen and uric acid markedly increased the depressed P-VASP levels and improved NTG sensitivity of the tolerant vasculature. CONCLUSIONS: Nitroglycerin-induced vascular peroxynitrite formation inhibits the activity of PGI(2)-S as well as NO, cGMP, and cGK-I signaling, which may contribute to vascular dysfunction in the setting of tolerance.

The oxidative stress concept of nitrate tolerance and the antioxidant properties of hydralazine.

The hemodynamic and anti-ischemic effects of nitroglycerin (NTG) are rapidly blunted as a result of the development of nitrate tolerance. With initiation of NTG therapy, it is possible to detect neurohormonal activation and intravascular volume expansion. These so-called pseudotolerance mechanisms may compromise the vasodilatory effects of NTG. Long-term nitrate treatment also is associated with decreased vascular responsiveness caused by changes in intrinsic mechanisms of the tolerant vasculature itself. According to the oxidative stress concept, increased vascular superoxide (O2-) production and an increased sensitivity to vasoconstrictors secondary to activation of protein kinase C contribute to the development of tolerance. Nicotinamide adenine dinucleotide phosphate oxidase and the uncoupled endothelial nitric oxide synthase may be O2- -producing enzymes. Nitric oxide (NO) and O2-, both derived from NTG and the vessel wall, form peroxynitrite in a diffusion-limited rapid reaction. Peroxynitrite, O2-, or both may be responsible for the development of nitrate tolerance and cross-tolerance to direct NO donors (eg, sodium nitroprusside, sydnonimines) and endothelium-dependent NO synthase-activating vasodilators. Hydralazine is an efficient reactive oxygen species (ROS) scavenger and an inhibitor of O2- generation. When given concomitantly with NTG, hydralazine prevents the development of nitrate tolerance and normalizes endogenous rates of vascular O2- production. Recent experimental work has defined new tolerance mechanisms, including inhibition of the enzyme that bioactivates NTG (ie, mitochondrial aldehyde dehydrogenase isoform 2 [ALDH2]) and mitochondria as potential sources of ROS. NTG-induced ROS inhibit the bioactivation of NTG by ALDH2. Both mechanisms increase oxidative stress and impair NTG bioactivation, and now converge at the level of ALDH2 to support a new theory for NTG tolerance and NTG-induced endothelial dysfunction. The consequences of these processes for NTG downstream targets (eg, soluble guanylyl cyclase, cyclic guanosine monophosphate-dependent protein kinase), toxic effects contributing to endothelial dysfunction (eg, prostacyclin synthase inhibition) and novel applications of the antioxidant properties of hydralazine are discussed.

Nebivolol prevents vascular NOS III uncoupling in experimental hyperlipidemia and inhibits NADPH oxidase activity in inflammatory cells.

OBJECTIVE: Nebivolol, in contrast to other selective beta1-adrenergic receptor antagonists like atenolol, improves endothelial function in patients with oxidative stress within vascular tissue. With the present studies we sought to determine whether beta receptor blockade with nebivolol may improve endothelial function in hyperlipidemia and whether this is attributable to reductions in vascular oxidative stress. METHODS AND RESULTS: Watanabe heritable hyperlipidemic rabbits (WHHL) were treated with nebivolol (10 mg/kg per day for 8 weeks). New Zealand white rabbits (NZWR) served as controls. Nebivolol improved endothelial function, reduced vascular superoxide and vascular macrophage infiltration, and prevented NO synthase uncoupling in WHHL. Nebivolol treatment did not modify the expression of sGC or cGK-I but improved cGK-I activity (assessed by the phosphorylation state of the VAsodilator Stimulated Phosphoprotein at serine239, P-VASP). NAD(P)H oxidase activity in whole blood and isolated neutrophils was dose-dependently inhibited by nebivolol, whereas atenolol, metoprolol, and carvedilol were markedly less effective. CONCLUSIONS: Nebivolol therapy effectively prevents NO synthase III uncoupling and prevents activation of the neutrophil NAD(P)H oxidase and infiltration of inflammatory cells. These novel antioxidative stress actions of this compound may explain partly the beneficial effects on endothelial function in patients with enhanced vascular oxidative stress.

[Surface ECG characteristics of right and left atrial flutter]. / Oberflächen-EKG-Charakteristika von rechts- und linksatrialem Vorhofflattern.

INTRODUCTION: Atrial tachycardia in virtually all areas of both atria has become more important in the clinical management of patients with previous complex atrial fibrillation ablation. Accurate interpretation of surface electrocardiogram (ECG) characteristics is of paramount importance to localize the origin of atrial tachycardia, particularly for planning interventional treatment. This article highlights the ECG features of different types of right and left atrial tachycardia. DEFINITION: Typical right atrial flutter through the cavotricuspid isthmus conducts septally in a cranial direction and demonstrates sawtooth-like flutter waves which start negative in II, III and aVF and then show a steep slope upwards to the isoelectric line. The flutter rate typically ranges between 240-250 beats/min. In contrast, right atrial flutter in a clockwise rotation, flutter around the vena cava inferior or superior and around a scar (e.g. after cardiac surgery) show positive or biphasic flutter waves (lower or upper loop reentry). Left atrial flutter waves (e.g. around the mitral valve or around the pulmonary veins) are very heterogeneous and are typically positive in V1 as the left atrium is located in the posterior mediastinum. CONCLUSION: Specific knowledge of flutter wave morphology in surface ECG facilitates planning and performance of the ablation strategy.