Cardiac cycle

About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.

Maximal Rate of Tachycardia Development: Sinus Tachycardia with Sudden Exercise vs. Spontaneous Ventricular Tachycardia

Abstract: In addition to providing basic physiologic information, knowledge of the maximal rate of sinus tachycardia development may be helpful in developing algorithms permitting new generations of antitachycardia pacemakers to distinguish accurately between sinus and ventricular tachycardia. To determine the maximal rate of sinus tachycardia development, 50 normal subjects rushed up 100 stairs as rapidly as possible, with continuous electrocardiographic monitoring. During the first second of exercise, the mean cardiac cycle length shortened from 709 to 570 ms, equivalent to an increase in heart rate from 85 to 105 beats per minute, or 20 beats per minute per second. Thereafter, a more gradual decrease in cycle length occurred. Differences between men and women, smokers and non-smokers, and sedentary compared to active subjects were all insignificant. Analysis of 50 spontaneous episodes of ventricular tachycardia also revealed a sequential but more abrupt decrease in the cycle length during the first second from 757 to 360 ms, equivalent to a rate increase from 79 to 167 beats per minute, or 88 beats per minute per second. After approximately 1 1/4 seconds, the ventricular tachycardia cycle length remained virtually constant. Baseline cycle lengths were similar in the sinus and ventricular tachycardia groups, but differed in all subsequent beats, although overlap for individual subjects did occur.

Assessment of left atrial dimensions by cross sectional echocardiography in patients with mitral valve disease.

Abstract: Left atrial dimensions were measured using cross sectional echocardiography in 37 patients with mitral valve disease and 30 normal subjects of similar ages. The anteroposterior (AP), superior-inferior (SI), and medial-lateral (ML) left atrial dimensions were determined at the end of ventricular systole using parasternal long and short axis and apical four chamber views (for SIa and MLa). To assess the reliability of these measurements cross sectional echocardiographic and angiographic left atrial volumes were compared in 19 patients with mitral valve disease, giving an excellent correlation. A moderate correlation was found between the anteroposterior dimension of the left atrium obtained using M mode echocardiography and that obtained using the parasternal short axis and long axis projections. In normal subjects a good correlation was found between SI and ML dimensions, while a lower correlation was found between SI and AP, and ML and AP dimensions. The SI dimension was the major axis of the left atrium and AP dimension the minor axis. In patients with mitral valve disease a good correlation was found between SI and ML dimensions, while SI and ML dimensions had a low correlation with AP dimensions. The AP dimension was the minor axis of the left atrium, while the SI and ML dimensions were not significantly different. All left atrial dimensions were significantly greater in patients with mitral valve disease than in normal subjects. Of 30 patients with at least one dimension increased, all three dimensions were abnormal in 16, two dimensions were increased in 10, and only one dimension was increased in four. AP, SI, and ML dimensions were abnormal in 25, 20, and 27 patients, respectively. Cross sectional echocardiography may provide a reliable estimate of left atrial dimensions. In patients with mitral valve disease a thorough examination of the left atrium using multiple cross sectional views is necessary to detect asymmetric left atrial enlargement and to measure the degree of left atrial dilatation.

A novel counterpulsation mode of rotary left ventricular assist devices can enhance myocardial perfusion

Abstract: The effect of rotary left ventricular assist devices (LVADs) on myocardial perfusion has yet to be clearly elucidated, and several studies have shown decreased coronary flow under rotary LVAD support. We have developed a novel pump controller that can change its rotational speed (RS) in synchronization with the native cardiac cycle. The aim of our study was to evaluate the effect of counterpulse mode, which increases the RS in diastole, during coronary perfusion. Experiments were performed on ten adult goats. The EVAHEART LVAD was installed by the left ventricular uptake and the descending aortic return. Ascending aortic flow, pump flow, and coronary flow of the left main trunk were monitored. Coronary flow was compared under four conditions: circuit-clamp, continuous mode (constant pump speed), counterpulse mode (increased pump speed in diastole), and copulse mode (increased pump speed in systole). There were no significant baseline changes between these groups. In counterpulse mode, coronary flow increased significantly compared with that in continuous mode. The waveform analysis clearly revealed that counterpulse mode mainly resulted in increased diastolic coronary flow. In conclusion, counterpulse mode of rotary LVADs can enhance myocardial perfusion. This novel drive mode can provide great benefits to the patients with end-stage heart failure, especially those with ischemic etiology.

Dynamic morphology of the secundum atrial septal defect evaluated by three dimensional transoesophageal echocardiography.

Abstract: OBJECTIVE—To define by three dimensional echocardiography the pattern and potential determinants of contraction of a secundum atrial septal defect through the cardiac cycle, and to evaluate the possibility of using cross sectional transthoracic and transoesophageal imaging to assess the dynamic nature of the defect. DESIGN—Three dimensional echocardiography was performed using a multiplane transoesophageal probe on 50 patients with a secundum atrial septal defect (median age 9.8 years). Nine patients were excluded because of poor images or morphological features that precluded defect measurement. In 41 cases, defect area, long and short axis length, and distance of the attenuated anterior rim were measured in their largest and smallest dimensions. RESULTS—Defect area changed significantly through the cardiac cycle (mean change 61%, p < 0.0001; range 17% to 86%). The defect contracted symmetrically and was not related to patient age, defect size, heart rate, Qp/Qs ratio, the presence of an aneurysmal atrial septum, or attenuated anterior rim. In all cases with an attenuated anterior rim (n = 13), the length of the rim significantly decreased (p = 0.001) during atrial systole. Dynamic changes measured by either transthoracic or transoesophageal cross sectional images did not correlate with those obtained by three dimensional imaging. CONCLUSIONS—Three dimensional echocardiography shows dynamic features of defects in the atrial septum. This information may lead to an improved understanding of the pathophysiology of atrial shunting. Keywords: echocardiography; atrial septal defect; congenital heart disease