A Review of Automatic Cardiac Segmentation using Deep Learning and Deformable Models
Kayvan Najarian, Delaram Kahrobaei, Enrique Domínguez, Reza Soroushmehr in Artificial Intelligence in Healthcare and Medicine, 2022
The cardiac cycle is defined as a sequence of alternating contractions and relaxations of the atria and ventricles in order to pump blood throughout the body. This cycle starts at the beginning of one heartbeat and ends at the start of the next. Each cardiac cycle has a diastolic phase (also called diastole) and a systolic phase (also called systole). Diastole occurs when the heart muscles relax, and the chambers are able to fill with blood. Systole occurs when the ventricles contract, pushing blood out of the right and left ventricles into the lungs and the rest of the body, respectively. Since manual delineation of ventricle contours in all cardiac phases is not possible, physicians focus only on end-diastole and end-systole phases for assessment of the cardiovascular system.
The transport and exchange systems: respiratory and cardiovascular
Nick Draper, Helen Marshall in Exercise Physiology, 2014
The ECG trace is normally described according to the three common deflections in the trace, the P wave, QRS complex and T wave. The P waverepresents the depolarisation of the atria, i.e. the spreading of an electrical impulse from the SA node that stimulates the atria to contract. The QRS complexdepicts the depolarisation of the ventricles propagated from the AV node via the Purkinje fibres to the ventricular muscle fibres. The T waverepresents the repolarisation of the ventricles ready for the next contraction. The repolarisation of the atria which takes place during the depolarisation of the ventricles is masked by the QRS complex and as such does not form an identifiable trace on an ECG. The period between the P and the R wave, called the P-R interval, represents the time for the atria to contract and then begin to relax (R is used rather than Q for this interval because the Q wave is often small). The same phase for the ventricles, from the start of contraction to the start of relaxation is known as the Q-T interval. The contraction phase of the cardiac cycle is known as systole and the relaxation phase as diastole.
Perfusion
Philip Woodrow in Nursing Acutely Ill Adults, 2015
Ventricles fill during diastole; during systole, valves between atria and ventricles should close, while active contraction prevents filling. Systole is the active phase of the cardiac cycle; diastole is whatever time is left between systoles. While the time of each systole will reduce with tachycardia, reduction in each systolic time is disproportionately less that increase in rate. Barrett et al. (2010) suggest that with heart rates of 60 bpm diastolic time is 0.62 seconds, while at rates of 200 bpm diastolic time is 0.14 seconds. So tripling heart rate reduces diastolic time (ventricular filling time) by three quarters. At heart rates of 200 bpm there will be much less blood in the ventricles each time they contract, therefore stroke volume will be far smaller.
Left atrial remodelling may predict exercise capacity in obstructive sleep apnoea patients
Published in Acta Cardiologica, 2018
Süha Çetin, Mustafa Vural, Ramazan Akdemir, Hikmet Fırat
Speckle tracking echocardiography (STE) was assessed off-line with commercially available software (Phillips Medical System, Bothell, Washington, USA). All STE images were obtained at a frame rate of 50–80 frames per second. The investigator marked the border of the LA endocardium and epicardium on an end-systolic frame. The software automatically traced the borders on subsequent frames. The verification of adequate tracking was performed in real-time and corrected by adjusting the area of interest or manually re-tracking the border to ensure optimal boundaries. End-systole has been identified through aortic valve closure measured by Doppler. The software QLAB 6.0 is also able to show deformation values in time-strain graphs. Consequently it is possible to identify different phases of the cardiac cycle.
Coronary CT angiography: a guide to examination, interpretation, and clinical indications
Published in Expert Review of Cardiovascular Therapy, 2021
Filippo Cademartiri, Giancarlo Casolo, Alberto Clemente, Sara Seitun, Cesare Mantini, Eduardo Bossone, Luca Saba, Nicola Sverzellati, Stefano Nistri, Bruna Punzo, Carlo Cavaliere, Ludovico La Grutta, Giovanni Gentile, Erica Maffei
The retrospective reconstructions use a reference point which is the R-wave of the QRS-complex of the ECG that corresponds to electrical wave that triggers contraction of the cardiac muscle. From this point, we can use a relative phase calculation by means of a percentage of the R-R interval approach or we can use an absolute forward or reverse approach in milliseconds. Usually, the best images are obtained in mid-to–end diastolic phase when the heart is at the end of diastolic filling and therefore motion is minimized. This particularly with heart rates below 65 bpm. This phase of the cardiac cycle is identifiable in the range of 55–85% (relative percentage approach) or −450/−250 ms (absolute reverse approach). When heart rates are progressively above 65 bpm it becomes more and more required to perform the so–called ‘systolic reconstructions’. This phase of the cardiac cycle is identifiable in the range of 25–40% (relative percentage approach) or +250/+400 ms (absolute forward approach) and corresponds to isovolumetric relaxation of the left ventricle (normal duration 70–100 ms).
Complications associated with myocardial bridging in four children without underlying cardiac disease: a case series
Published in Paediatrics and International Child Health, 2021
Federica Brancato, Donato Rigante, Marco Piastra, Alessandro Gambacorta, Claudia Aurilia, Gabriella De Rosa
One of the most important triggers of symptomatic MB is intense physical activity which through tachycardia and increased contractility can facilitate myocardial ischaemia. During tachycardia, systole occupies a greater proportion of the cardiac cycle because of shortening of the diastolic filling period. Other pathophysiological factors that might reveal or exacerbate MB are age, left ventricular hypertrophy and coronary atherosclerosis, since all of these may worsen the supply-demand mismatch imposed by the bridge, reducing the coronary reserve [15]. Symptomatic patients may also present with clinical manifestations of myocardial ischaemia such as acute coronary syndrome, coronary spasm, exercise-induced dysrhythmias, myocardial stunning, transient ventricular dysfunction and syncope [15]. Only patients with symptomatic MB or those with objective signs of ischaemia require treatment. In most cases, beta-blockers, ivabradine and calcium channel blockers are effective in reducing symptoms [15]. In adults, myotomy, coronary artery by-pass surgery and stenting may be used to improve symptoms in patients with MB who are refractory to medical therapy [2,20,22,23]. MB is diagnosed by coronary or CT angiography, but it is sometimes established intra-operatively or at post-mortem examination. Another relevant diagnostic test is the stress ECG: the main objective of stress testing for myocardial ischaemia is to demonstrate the mismatch between myocardial oxygen demand and myocardial perfusion [22].