A fast algorithm for spatiotemporal signals recovery using arbitrary dictionaries with application to electrocardiographic imaging.

This paper presents a method to solve a linear regression problem subject to grouplassoand ridge penalisation when the model has a Kronecker structure. This model was developed to solve the inverse problem of electrocardiography using sparse signal representation over a redundant dictionary or frame. The optimisation algorithm was performed using the block coordinate descent and proximal gradient descent methods. The explicit computation of the underlying Kronecker structure in the regression was avoided, reducing space and temporal complexity. We developed an algorithm that supports the use of arbitrary dictionaries to obtain solutions and allows a flexible group distribution.

Sex differences on the electrocardiographic pattern of cardiac repolarization: possible role of testosterone.

BACKGROUND: Cardiac repolarization has been shown to be shorter and faster in men compared with women. In this study, we examined the electrocardiographic pattern of repolarization in patients with abnormal plasma levels of testosterone to gain insight into the role that this hormone plays in modulating repolarization. METHODS AND RESULTS: Repolarization was measured in 27 castrated men, 26 women with virilization, and 53 control subjects pair-matched for age and sex. Repolarization in castrated men was slower and longer than that of normal men. Women with virilization exhibited a shorter and faster repolarization than normal women and castrated men. These differences are the opposite of those found in the normal population. Finally, the changes observed in castrated men may be reverted by testosterone. CONCLUSIONS: We conclude that testosterone plays an important role in modulating cardiac repolarization.

Effect of electrode impedance in improved buffer amplifier for bioelectric recordings.

We analysed the effects of electrode impedance on the transfer response of a one-stage improved buffer amplifier. The electrode DC resistance (R(d)) modifies the one-stage buffer transfer response. We found a limit electrode resistance (R(d(lim))) which depends on the transfer damping factor (epsilon). If R(d) is lower than 86.5 komega, the transfer response of the buffer fulfils American Heart Association (AHA) recommendations, but when R(d) is greater than R(d(lim)) it must be cautiously weighed up because its influence in the transfer response becomes appreciable. The maximum R(d) that can be driven by the buffer is 1.2 Momega. Higher values do not fulfil AHA recommendations. Therefore, electrodes with higher impedance should not be used with this kind of buffer. In contrast, when this buffer is used to build in an instrumentation amplifier (IA) for bipolar recording, the common-mode rejection ratio (CMRR) is sensitive to the electrode type used.

Cardiac risk assessment: when and who? [Retrospectroscope].

Think about the above lines taken from the Old Testament: At 130 years of age, Adam begat a son and at 800 he kept going, quitting this earthly life at 930. These numbers surpass by far the limits our current experience teaches us, however, perhaps a life span into the hundreds of years is ? What if, in the future, science were to do away with disease? What then would cause people to die: accidents, killings, wars? How old would old age be? Aging has always been a hot topic for research (with considerable quackery, too). For example, animals with a slow metabolism tend to live longer than those with a fast metabolism. Compare the average life span of a mouse with that of a turtle. Apparently, meditators are able to slow their metabolism down [1].

Differential channeling of sensory stimuli onto a motor neuron in the leech.

We studied a specific sensory-motor pathway in the isolated leech ganglia. Pressure-sensitive mechanosensory neurons were stimulated with trains of action potentials at 5-20 Hz while recording the responses of the annulus erector motorneurons that control annuli erection. The response of the annulus erector neurons was a succession of excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials. The excitatory postsynaptic potentials had a brief time-course while the inhibitory postsynaptic potentials had a prolonged time-course that enabled their temporal summation. Thus, the net effect of pressure-sensitive neuron stimulation on the annulus erector neurons was inhibitory. Both phases of the response were mediated by chemical transmission; the excitatory postsynaptic potentials were transmitted via a monosynaptic pathway, and the inhibitory postsynaptic potentials via a polysynaptic one. The pattern of expression of this dual response depended on the field of innervation of the sensory neuron and it was under the influence of cell 151, a non-spiking interneuron, that could regulate the expression of the hyperpolarization. The interaction between pressure-sensitive neurons and annulus erector neuron reveals how sensory specificity, connectivity pattern and regulatory elements interplay in a specific sensory-motor network.

Differential modulation of electrocardiographic indices of ventricular repolarization dispersion depending on the site of pacing during premature stimulation.

INTRODUCTION: Dispersion of ventricular repolarization has been shown to increase with premature stimulation. Moreover, a straight correlation between the amount of dispersion of repolarization and the vulnerability to ventricular fibrillation was reported. On the other hand, differences between right ventricular (RV) and left ventricular (LV) fibrillation threshold have been reported. However, no data exist regarding the influence of the site of stimulation on modulation of dispersion of repolarization. METHODS AND RESULTS: In the present study, several ECG indices of dispersion of repolarization, as a function of the coupling interval and the site of stimulation, were evaluated in a modified Langendorff-perfused rabbit heart (n = 12), with a 5 x 8 array of a simulated body surface unipolar lead system. As the coupling interval was shortened, a biphasic modulation of dispersion of repolarization was found when stimuli were elicited at the LV. In contrast, when the heart was paced from the RV, the dispersion increased monotonically as coupling interval was shortened. CONCLUSION: A differential behavior of the modulation of dispersion of repolarization was found as a function of the site of stimulation.

Influence of filtering techniques on the time-domain analysis of signal-averaged P wave electrocardiogram.

INTRODUCTION: The advent of signal-averaged ECG (SAECG) systems for P wave analysis has made it important to determine if the use of different filtering techniques in these systems is diagnostically equivalent. METHODS AND RESULTS: Three different high-pass filtering techniques and two cutoff frequency values were used: 29- and 40-Hz Butterworth bidirectional filter (BB29, BB40), 29- and 40-Hz Butterworth unidirectional filter (UB29, UB40), and 29- and 40-Hz least mean square filter (LMS29, LMS40). Normal healthy volunteers (n = 36) and patients with documented paroxysmal atrial fibrillation (n = 23) were analyzed. A custom-built SAECG system and standard bipolar orthogonal leads were used. Noise was reduced to < 0.3 microV. P wave total duration, root mean square voltage of the terminal 20, 30, and 40 msec of the filtered vector magnitude, and the area under the curve between the onset and offset of averaged unfiltered and filtered P wave vector magnitude were analyzed. Only the duration of the P wave showed statistically significant differences between groups, being longer in the PAF group for all filters and cutoff frequencies studied. A bias increment of approximately 20 msec was detected in unidirectional and least mean square filters as compared to the bidirectional filter. Sensitivity, specificity, and predictive accuracy were > 70% for all filters; the BB40 filter yielded the best performance. CONCLUSION: The normality limits derived from one filter cannot be applied directly to recordings obtained from the other filters. Critical limits must be established individually for different software settings.

Sex-dependent electrocardiographic pattern of cardiac repolarization.

BACKGROUND: Although sex-dependent differences in cardiac repolarization have been known for many years, few attempts have been carried out to define the individual contribution of each electrocardiographic (ECG) repolarization variable to the sex-dependent pattern. METHOD AND RESULTS: We analyzed several ECG repolarization variables that reflect both the duration and the rate of repolarization in 500 normal healthy subjects between the ages of 20 and 80 years (250 men and 250 women) and distributed into 5 groups according to age. Cardiac repolarization, measured in the precordial lead exhibiting the highest T-wave amplitude, was found to be shorter and faster in normal men compared with normal women (P <.001). The parameters with the highest individual weight in determining these sex differences were the J point and the ST angle, as indicated by nonlinear (logistic) multivariate regression analysis. CONCLUSION: We conclude that changes in the duration and rate of early repolarization are determinants for these sex-dependent ECG pattern differences.