Are plasma natriuretic peptide levels influenced by automatic pacemaker algorithms for ventricular pacing minimization?

BACKGROUND: Automatic atrioventricular search hysteresis (AVSH) is designed to reduce the cumulative percentage of potentially deleterious right ventricular apical pacing (VP%) in dual-chamber pacemakers. We investigated whether minimizing VP% by AVSH can, in turn, reduce ventricular wall stretching/stress, as assessed by plasma concentrations of the amino-terminal fragment of the pro-B-type natriuretic peptide (NT-proBNP). METHODS: After dual-chamber pacemaker implantation in 81 patients (age: 69 ± 11 years; males: 55.6%), the fixed atrioventricular delay of 225 ms was programmed and AVSH was turned off for 1 month. The patients were thereafter randomly assigned to standard AVSH for 1 month, followed by an enhanced AVSH for another month, or vice versa. At the 1-, 2-, and 3-month follow-ups, VP% values were retrieved from the pacemaker memory, and venous blood samples were taken for NT-proBNP measurements. RESULTS: Both standard and enhanced AVSH reduced the median VP% value from 38.5% (for the fixed atrioventricular delay) to 2.1% (P < 0.001). However, plasma NT-proBNP concentrations for the fixed atrioventricular delay (median, 253 pg/mL), standard AVSH (225 pg/mL), and enhanced AVSH (276 pg/mL) did not differ significantly on the intrapatient basis (paired Wilcoxon tests) between any pair of these modalities. CONCLUSION: Minimizing ventricular pacing by AVSH during 1 month had no influence on plasma NT-proBNP levels (i.e., ventricular wall stretching/stress) compared with a constant, moderately prolonged atrioventricular delay.

Reduction of right ventricular pacing with advanced atrioventricular search hysteresis: results of the PREVENT study.

BACKGROUND: Right ventricular pacing predisposes to the development of heart failure and atrial fibrillation. Automatic atrioventricular search hysteresis (AVSH) is a commonly used strategy to decrease the percentage of right ventricular pacing (%VP) in patients without permanent AV block, but the results have not been optimal. METHODS: The randomized, crossover PREVENT study evaluated whether an enhanced AVSH with two new features can reduce %VP compared with standard AVSH. The new features are the repetitive hysteresis [switch from extended to basic AV delay after a consistent loss of intrinsic AV conduction (IAVC) lasting for six consecutive atrial cycles] and the scan hysteresis (periodic IAVC search extension over six consecutive atrial cycles). Both standard AVSH and enhanced AVSH performed a periodic IAVC search every 180 cardiac cycles and operated with a basic AV-delay of 225 ms and a rate-independent maximum AV-delay of 300 ms for paced and sensed atrial events. RESULTS: Among 178 patients, 53.4% had no evidence of AV block at enrollment and 46.6% had history of intermittent AV block. The median %VP was decreased by enhanced AVSH compared to standard AVSH (4.0% vs 5.5%, P < 0.001), particularly in patients with a history of AV block (21.4% vs 25.5%, P < 0.001). The primary study hypothesis that 25% of all patients would experience > 20% relative %VP reduction was not met as 46 (25.8%) patients (95% confidence interval, 20.5-31.8%) presented such relative reduction. CONCLUSION: The enhanced AVSH algorithm reduces %VP compared with standard AVSH in patients with intermittent AV block.

Undetected malignancies of the breast: dynamic contrast-enhanced MR imaging at 1.0 T.

PURPOSE: To assess the prevalence and characteristics of malignant breast lesions not identified with magnetic resonance (MR) imaging. MATERIALS AND METHODS: Breast tissue specimens were obtained in 464 of 967 patients who had undergone dynamic gadolinium-enhanced T1-weighted fast low-angle shot three-dimensional MR imaging of both breasts. A comparison of sensitivity, specificity, and predictive values of the prospectively recorded findings of mammography, ultrasonography (US), and MR imaging with the histopathologic results was performed with receiver operating characteristic (ROC) curve analysis. MR imaging examination findings that caused a false-negative diagnosis were reviewed to identify possible sources of error. RESULTS: Histopathologic analysis revealed 244 benign and 354 malignant lesions. The sensitivity values for mammography, mammography combined with US, MR imaging alone, and the combination of all three modalities were 73.7%, 88.1%, 88.4%, and 95.5%, and the areas under the ROC curves were 0.744, 0.829, 0.850, and 0.876, respectively. Twenty-eight (8.4%) of 334 invasive and 13 (65%) of 20 intraductal carcinomas were missed with MR imaging. In eight cases, motion artifacts (n = 1), tumor location near or beyond the outer boundary of the field of view (n = 3), inadequate infusion of the contrast material (n = 1), and masking of the tumors by intensively enhanced surrounding glandular tissue (n = 3) were identified as adequate explanations for the false-negative results. The remaining missed breast cancers (n = 33) exhibited very diffuse growth patterns or were 5 mm or smaller. CONCLUSION: MR imaging did not depict 41 of 354 malignant tumors for several reasons.

New determination of the electron's mass.

A new independent value for the electron's mass in units of the atomic mass unit is presented, m(e) = 0.000 548 579 909 2(4) u. The value is obtained from our recent measurement of the g factor of the electron in (12)C(5+) in combination with the most recent quantum electrodynamical (QED) predictions. In the QED corrections, terms of order alpha(2) were included by a perturbation expansion in Zalpha. Our total precision is three times better than that of the accepted value for the electron's mass.