Background-The relative contribution of the atrial septum and interatrial connections to biatrial activation is a fundamental concept of human cardiac electrophysiology that has yet to be fully characterized. The purpose of the present study was to determine how both atria are coupled electrically. Methods and Results-Twenty patients (16 men; mean age 54Ϯ11years) with a history of symptomatic atrial fibrillation (AF) underwent simultaneous biatrial noncontact mapping before catheter ablation of AF. The multiple electrode array catheters were positioned, respectively, in the left atrium (LA; transseptally) and the right atrium (RA). In all but 2 patients, isopotential maps revealed that endocardial septal activations of the RA and LA were separate, independent, and asynchronous of each other. Interatrial conduction was related to the site of initial atrial depolarization, revealing conduction over Bachmann's bundle in all patients during sinus rhythm, high RA pacing, and pacing from the LA appendage. Pacing from the coronary sinus was associated with conduction over the interatrial connection at the level of the coronary sinus in all patients, and conduction over Bachmann's bundle also occurred in 5 (26%) of 19 patients. Interatrial conduction over the fossa ovalis occurred in only 2 (2%) of the 116 segments analyzed. Conclusions-Electrical coupling of the RA and LA in humans is predominantly provided by muscular connections at the level of Bachmann's bundle and the coronary sinus. The true septum (the fossa ovalis and its limbus) of the RA and LA is asynchronous and discordant, usually without contralateral conduction during sinus rhythm or atrial pacing.

NavX(TM) mapping reduced ablation fluoroscopy times for accessory pathways during pediatric catheter ablation.

The heart rate (HR)-minute ventilation (VE) relationship has been shown to be nonlinear and can be expressed as two distinct straight lines. This study is to assess the correlation of the initial HR-VE slope to clinical parameters. Maximum treadmill exercise tests were performed in 100 healthy volunteers (age 19-77 years) using a ramp protocol in which work-rate increases linearly with exercise. Breath-by-breath VO2, VCO2, and VE were measured, and HR and BP were monitored throughout the exercise. The HR-VE curve demonstrated nonlinearity with a breakpoint determined by a change point analysis. This breakpoint was significantly higher than that of the anaerobic threshold. The VE at the HR-VE breakpoint was 56.4 +/- 19.4 and VE at the VE-VO2-VO2 breakpoints were 48.0 +/- 18.3 (P < 0.0001) and 40.1 +/- 16.5 (P < 0.0001), respectively. The HR at this HR-Ve breakpoint was 77.7 +/- 12.9% of the HR range. The first slope, S1 (1.76 +/- 0.64) was steeper than the second slope, S2 (0.66 +/- 0.39). Although there was a gender difference for S1, the best clinical predictor on a stepwise multiple regression analysis was body surface area (BSA) which explained 47% of the variance. It was concluded that nonlinearity of the HR-VE curve can be expressed as two straight lines. The breakpoint is beyond the anaerobic threshold and can be estimated to be approximately 75% of the maximal predicted HR. BSA is the only clinical parameter that significantly predicts the initial slope of the HR-VE curve. This can be of great importance in the programming of rate-adaptive pacemakers using a VE.

Transforming growth factor-1 expression in dilated cardiomyopathyTransforming growth factor-1 (TGF-1 ) is a multifunctional cytokine that has an important role in the regulation of cell growth, differentiation, and repair in a variety of tissues. 1In addition to its role in the cell cycle and apoptosis, TGF-1 induces the synthesis of extracellular matrix (ECM) and is upregulated by angiotensin II.1 2 Dilated cardiomyopathy is characterised by myocyte loss, hypertrophy of residual myocytes, increased interstitial fibrosis, and abnormalities of the cytoskeleton.3 Cytotoxic lymphocytes and macrophages are also present in the myocardium in increased numbers which may provide a source of TGF-1 . 4 Therefore in this study we have investigated whether patients with chronic heart failure caused by idiopathic dilated cardiomyopathy have increased plasma concentrations of TGF-1 , and whether this is associated with increased macrophage gene expression for TGF-1 compared to those with normal left ventricular function. Patients with ischaemic or hypertensive heart disease were excluded because of the potential confounding eVects on TGF-1 concentrations of atherosclerosis and pressure overload with left ventricular hypertrophy.Twenty patients who presented with symptoms and signs of chronic heart failure with no obvious cause and with the clinical diagnosis of dilated cardiomyopathy (by the World Health Organization criteria) were studied. All patients had right and left cardiac catheterisation with standard haemodynamic measurements, and coronary angiography was performed to exclude significant valvar, coronary artery disease, hypertensive heart failure, as well as constrictive pericardial disease or restrictive cardiomyopathy before proceeding to right ventricular biopsy. Twenty age and sex matched healthy controls with no evidence of cardiac disease (all with normal echocardiograms) were also studied. Serum TGF-1 was assayed with an enzyme linked immunosorbent assay (ELISA) (R & D System, Minneapolis, USA) The intra-and interassay coeYcient of variation was < 15%. Peripheral blood mononuclear cells were isolated and were resuspended in medium for total cell counting. CD14 cells were isolated using dynabeads M-450 CD14 (Dynal, AS, Oslo, Norway). The cells were incubated at 37°C in a humidified 5% carbon dioxide atmosphere, in the presence of phytohaemagglutinin (10 µg/ml) and Phorbol 12-myristate 13 acetate (1 ng/ml). The cells were harvested at time 0 and 24 hours after stimulation for total RNA extraction. After RNA extraction TGF-1 gene expression was quantified by the PCR MIMIC method (Clontech, Palo Alto, California, USA). Clontech, primers sequences are: 5' GCC CTG GAC ACC AAC TAT TGC T 3' and 5' AG GCT CCA AAT GTA GGG GCA GG 3'. The PCR product generated from MIMIC fragment has 270 bp while those from target cDNA has 161 bp, and were separated by 1.7-2% agarose gels and stained with ethidium bromide. Densitometry was performed and a standard curve was established by plotting the log value of the band intensity ratio...

No abstract