Cardiac cycle

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

Variation of lateral ventricular volume during the cardiac cycle observed by MR imaging.

Abstract: CSF pulsation suggests variation in the size of the cerebral ventricles during the cardiac cycle. The arterial blood flow and venous outflow are two major components that contribute to the variation. High-resolution MR imaging with cardiac gating provides sharp delineation of the cerebral ventricles with clear boundaries. Subtle changes in the size of the ventricles during the cardiac cycle are measurable with high precision and accuracy by using a sophisticated automated edge-detection algorithm. In 12 normal individuals, the cerebral ventricles were examined, and the size of the lateral ventricles showed a 10–20% change during the cardiac cycle. The pattern is complex but similar in appearance to the intracranial pressure pulse waveform. The variation suggests that the choroid plexus may play a greater role as a source of CSF pulsation than currently acknowledged.

Implantable cardiac device providing repetitive non-reentrant ventriculo-atrial synchronous (RNRVAS) rhythm therapy using VA interval extension and method

Abstract: A system and method detects and terminates a repetitive non-reentrant ventriculo-atrial synchronous (RNRVAS) rhythm. The system and method is particularly adapted for use in an implantable cardiac stimulation device including a pulse generator that delivers atrial and ventricular pacing stimulation pulses to a heart which implements an AV delay and an atrial escape interval. The system includes a sensing circuit that senses cardiac activity of the heart and a detector responsive to the sensing circuit that determines if an RNRVAS rhythm is present. When an RNRVAS rhythm is present, a therapy control circuit lengthens the atrial escape interval for at least one cardiac cycle. In addition, the VA delay interval may be shortened by the same amount to maintain a consistent ventricular pacing rate.

His-bundle capture verification and monitoring

Abstract: This document discusses, among other things, a system and method for generating a stimulation energy to provide His-bundle stimulation for a cardiac cycle, receiving electrical information from the heart over at least a portion of the cardiac cycle, determining a characteristic of at least a portion of the received electrical information for the cardiac cycle, and classifying the cardiac cycle using the determined characteristic.

Delayed depolarization of the cog-wheel valve and pulmonary-to-systemic shunting in alligators.

Abstract: SUMMARY Alligators and other crocodilians have a cog-wheel valve located within the subpulmonary conus, and active closure of this valve during each heart beat can markedly and phasically increase resistance in the pulmonary outflow tract. If this increased resistance causes right ventricular pressure to rise above that in the systemic circuit, right ventricular blood can flow into the left aorta and systemic circulation, an event known as pulmonary-to-systemic shunting. To understand better how this valve is controlled, anaesthetized American alligators ( Alligator mississippiensis ) were used to examine the relationships between depolarization of the right ventricle, depolarization/contraction of the cog-wheel valve muscle and the resultant right ventricular, pulmonary artery and systemic pressures. Depolarization swept across the right ventricle from the apex towards the base (near where the cog-wheel valve muscle is located) at a velocity of 91±23 cm s -1 (mean ± S.E.M., N =3). The cog-wheel valve electrocardiogram (ECG) (and thus contraction of the valve) trailed the right ventricular ECG by 248±28 ms ( N =3), which was equivalent to 6-35 % of a cardiac cycle. This long interval between right ventricular and valve depolarization suggests a nodal delay at the junction between the base of the right ventricle and the cog-wheel valve. The delay before valve closure determined when the abrupt secondary rise in right ventricular pressure occurred during systole and is likely to strongly influence the amount of blood entering the pulmonary artery and thus to directly control the degree of shunting. Left vagal stimulation (10-50 Hz) reduced the conduction delay between the right ventricle and cog-wheel valve by approximately 20 % and reduced the integrated cog-wheel ECG by 10-20 %. Direct application of acetylcholine (1-2 mg) also reduced the integrated cog-wheel ECG by 10-100 %; however, its effect on the conduction delay was highly variable (-40 to +60 %). When the cog-wheel valve muscle was killed by the application of ethanol, the cog-wheel ECG was absent, right ventricular and pulmonary pressures remained low and tracked one another, the secondary rise in right ventricular pressure was abolished and shunting did not occur. This study provides additional, direct evidence that phasic contraction of the cog-wheel valve muscle controls shunting, that nervous and cholinergic stimulation can alter the delay and strength of valve depolarization and that this can affect the propensity to shunt.