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Fiber Shortening (fiber + shortening)
Selected AbstractsAcute Cardiac Effects of Nicotine in Healthy Young AdultsECHOCARDIOGRAPHY, Issue 6 2002Catherine D. Jolma M.D. Background: Nicotine is known to have many physiologic effects. The influence of nicotine delivered in chewing gum upon cardiac hemodynamics and conduction has not been well-characterized. Methods: We studied the effects of nicotine in nonsmoking adults (6 male, 5 female; ages 23,36 years) using a double-blind, randomized, cross-over study. Subjects chewed nicotine gum (4 mg) or placebo. After 20 minutes (approximate time to peak nicotine levels), echocardiograms and signal-averaged electrocardiograms (SAECG) were obtained. After 40 minutes, subjects were again given nicotine gum or placebo in cross-over fashion. Standard echocardiographic measurements were made from two-dimensional images. We then calculated end-systolic wall stress (ESWS), shortening fraction (SF), systemic vascular resistance (SVR), velocity for circumferential fiber shortening corrected for heart rate (Vcfc), stroke volume, and cardiac output. P wave and QRS duration were measured from SAECG. Results: Significant differences (P < 0.05) from control or placebo were found for ESWS, mean blood pressure, cardiac output, SVR, heart rate, and P wave duration. No significant changes were seen in left ventricular ejection time (LVET), LV dimensions, SF, contractility (Vcfc), or QRS duration. Conclusions: These results suggest that nicotine chewing gum increases afterload and cardiac output. Cardiac contractility does not change acutely in response to nicotine gum. Heart rate and P wave duration are increased by chewing nicotine gum. [source] Relationship Between Regional Shortening and Asynchronous Electrical Activation in a Three-Dimensional Model of Ventricular ElectromechanicsJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2003TARAS P. USYK Ph.D. Introduction: Asynchronous electrical activation can cause abnormalities in perfusion and pump function. An electromechanical model was used to investigate the mechanical effects of altered cardiac activation sequence. Methods and Results: We used an anatomically detailed three-dimensional computational model of the canine ventricular walls to investigate the relationship between regional electrical activation and the timing of fiber shortening during normal and ventricular paced beats. By including a simplified Purkinje fiber network and anisotropic impulse conduction in the model, computed electrical activation sequences were consistent with experimentally observed patterns. Asynchronous time courses of regional strains during beats stimulated from the left or right ventricular epicardium showed good agreement with published experimental measurements in dogs using magnetic resonance imaging tagging methods. When electrical depolarization in the model was coupled to the onset of local contractile tension development by a constant time delay of 8 msec, the mean delay from depolarization to the onset of systolic fiber shortening was 14 msec. However, the delay between the onset of fiber tension and initial shortening varied significantly; it was as late as 60 msec in some regions but was also as early as ,50 msec (i.e., 42 msec before depolarization) in other regions, particularly the interventricular septum during free-wall pacing. Conclusion: The large variation in delay times was attributable to several factors including local anatomic variations, the location of the site relative to the activation wavefront, and regional end-diastolic strain. Therefore, we conclude that these factors, which are intrinsic to three-dimensional ventricular function, make the regional sequence of fiber shortening an unreliable surrogate for regional depolarization or electromechanical activation in the intact ventricles. (J Cardiovasc Electrophysiol, Vol. 14, pp. S196-S202, October 2003, Suppl.) [source] Relation Between the Pacing Induced Sequence of Activation and Left Ventricular Pump Function in AnimalsPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 4 2002FRITS W. PRINZEN PRINZEN, F.W., et al.: Relation Between the Pacing Induced Sequence of Activation and Left Ventricu-lar Pump Function in Animals. The main goal of this article was to review animal experimental work on the effect of asynchronous activation on ventricular pump function. During normal sinus rhythm and atrial pacing, the Purkinje system contributes significantly to the rapid electrical activation of the ventricles. In contrast, during ventricular pacing the impulse is almost exclusively conducted through the normal myocardium. As a consequence, electrical activation of the ventricles becomes asynchronous and has an abnormal sequence. The abnormal impulse conduction causes considerable disturbances to occur in regional systolic fiber shortening, mechanical work, blood flow, and oxygen consumption; low values occurring in early activated regions and values above normal being present in late activated regions. Many animal studies have now shown that the abnormal electrical activation, induced by ventricular pacing, leads to a depression of systolic and diastolic LV function. Pacing at the right ventricular apex (the conventional pacing site) reduces LV function more than pacing at the high ventricular septum or at LV sites. In canine hearts with experimental LBBB, LV pacing significantly improves LV pump function. Differences in LV pump function between (combinations of) pacing sites are poorly correlated with QRS duration. Therefore, the cause of the depression of LV function during abnormal electrical activation appears to be a combination of the asynchrony and the sequence of activation. These experimental findings justify continuing attention for optimizing the site(s) of ventricular pacing in patients with normal and abnormal ventricular impulse conduction. [source] B-type natriuretic peptide as a marker for cardiac dysfunction in anthracycline-treated childrenPEDIATRIC BLOOD & CANCER, Issue 6 2007Sanjeev Aggarwal MD Abstract Background Anthracyclines (AC) are useful antineoplastic agents, whose utility is limited by progressive cardiotoxicity. Our purpose was to evaluate plasma B-type natriuretic peptide (BNP), as a screening test for detecting late cardiac dysfunction in AC-treated children and to determine the prevalence of late cardiac dysfunction at low cumulative AC doses. Materials and Methods This was a prospective study in which patients who had completed AC therapy at least 1 year earlier, underwent a detailed echocardiogram and a simultaneous BNP level. Cardiac dysfunction was defined as any one of the following: shortening fraction (FS) <29%, rate corrected velocity of circumferential fiber shortening (VCFc) <0.9 c·sec,1, end systolic wall stress (ESWS) >60 g·cm,2, abnormal VCFc: ESWS ratio or decreased mitral inflow velocity (E/A) ratios, compared to age-specific norms. Results The cohort (n,=,63) included 37 males with a median age of 13.1 years (range, 6.5,26.5 years). Cardiac dysfunction was found in 26 (41%) patients and in 40% of patients who received cumulative doses <150 mg·m,2. ESWS was the most common abnormality. Mean BNP levels in the subset with abnormal function were significantly higher than the normal group (23.4,±,25.3 vs. 14.2,±,8.9 pg·ml,1, P,=,0.02). Conclusions Plasma BNP was significantly elevated in AC-treated patients with late cardiac dysfunction, although there was considerable overlap of levels between groups with and without cardiac dysfunction. BNP may need further evaluation as a serial index of cardiac function in this population. Cardiac dysfunction was observed in a significant proportion of patients, even at low cumulative AC doses. Pediatr Blood Cancer 2007;49:812,816. © 2006 Wiley-Liss, Inc. [source] Subclinical Left Ventricular Dysfunction in Migraine AttacksHEADACHE, Issue 1 2006Manuel Vidalón MD Objective.,The aim of the present study was to evaluate cardiac performance of patients with migraine attacks during the overload produced by phenylephrine infusion. Background.,It is known that circulatory changes occur during migraine. However, the relationship between this finding and transient cardiac dysfunction is still unknown. Methods.,By means of two-dimensional direct M-mode echocardiography, we measured fractional shortening, ejection fraction, and mean velocity of circumferential fibers shortening in 18 patients with migraine and in 10 normal subjects as a control group. These measures were performed in two different periods: during attack-free intervals and during attacks. Pain intensity of typical migraine attack was evaluated on a 0 to 10 scale. Results.,Cardiac size and function were normal at rest in both groups. However, during migraine attacks, phenylephrine infusion provoked significant decrease in fractional shortening, EF, and mean velocity of circumferential fibers shortening, followed by concomitant increase of headache severity. On the other hand, during the attack-free interval and in the control group phenylephrine infusion did not show significant changes in cardiac function parameters. Conclusions.,Our data suggest that left ventricular dysfunction during the phenylephrine test could participate in the complex pathophysiological mechanism of migraine attacks. [source] | ||||||||||