Effect of myocardial fiber direction on epicardial potentials.

BACKGROUND Understanding the relations between the architecture of myocardial fibers, the spread of excitation, and the associated ECG signals is necessary for addressing the forward problem of electrocardiography, that is, predicting intracardiac and extracardiac ECGs from known intracardiac activity. So far, these relations have been studied experimentally only in small myocardial areas. In this study, we tested the hypothesis that potential distributions measured over extensive epicardial regions during paced beats reflect the direction of superficial and intramural fibers through which excitation is spreading in both the initial and later stages of ventricular excitation. We also tried to establish whether the features of the epicardial potential distribution that correlate with fiber direction vary as a function of pacing site, intramural pacing depth, and time elapsed after the stimulus. An additional purpose was to compare measured epicardial potentials with recently published numerical simulations depicting the three-dimensional spread of excitation in the heart muscle and the associated potential fields. METHODS AND RESULTS The hearts of 18 mongrel dogs were exposed and 182 to 744 unipolar electrograms were recorded from epicardial electrode arrays (2.3 x 3.0 to 6.5 x 6.5 cm). Hearts were paced at various intramural depths through an intramural needle. The overall number of pacing sites in 18 dogs was 241. Epicardial potential distributions, electrographic waveforms, and excitation time maps were displayed, and fiber directions in the ventricular wall underlying the electrodes were determined histologically. During the early stages of ventricular excitation, the position of the epicardial maxima and minima revealed the orientation of myocardial fibers near the pacing site in all cases of epicardial and intramural pacing and in 60% of cases of endocardial or subendocardial pacing. During later stages of propagation, the rotation and expansion of the positive areas correlated with the helical spread of excitation through intramurally rotating fibers. Marked asymmetry of potential patterns probably reflected epicardial-endocardial obliqueness of intramural fibers. Multiple maxima appeared in the expanding positive areas. CONCLUSIONS For 93% of pacing sites, results verified our hypothesis that epicardial potential patterns elicited by ventricular pacing reflect the direction of fibers through which excitation is spreading during both the initial and later stages of propagation. Epicardial potential distributions provided information on the site of origin and subsequent helical spread of excitation in an epicardial-endocardial, endocardial-epicardial, or double direction. Results were in agreement with previously published numerical simulations except for the asymmetry and fragmentation of the positive areas. </jats:sec

Potential health economic impact of intravenous iron supplementation to erythropoiesis-stimulating agent treatment in patients with cancer- or chemotherapy-induced anemia

Background: Intravenous (i.v.) iron supplementation significantly improves the response to erythropoiesis-stimulating agent (ESA)-based therapies in patients with cancer- or chemotherapy-induced anemia. The economic implications of adding i.v. iron to ESA treatment are less well investigated. Published randomized controlled trials do not provide sufficient data for a comprehensive cost-effectiveness analysis. Methods: Preliminary cost calculations from the Swiss health care system perspective based on a meta-analysis and published results of eight randomized controlled trials without correction for decreased ESA need provide a conservative cost-effectiveness estimate. Results: The additional total cost of i.v. iron supplementation ranged from EUR 417 to EUR 901 per patient depending on the evaluated iron-carbohydrate complex. Considering a 24% absolute increase in the proportion of ESA responders, the incremental cost-effectiveness ratios per additional responder are EUR 1,704-3,686. In routine practice, better values may be achieved due to ESA dose savings. Conclusion: Supplementation of ESAs with i.v. iron appears to be an economically viable treatment option in anemic cancer patients. Additional research on ESA dose savings and cost-effectiveness is required