Cardiac bicycle of the left side of the heart. The electrocardiogram (EKG) below the diagram mirrors the corresponding waves v each step of the cardiac cycle. The bottom heat represents the first and 2nd heart sounds.

You are watching: When do the av valves close


The cardiac cycle to represent the hemodynamic and electric alters that take place in systole and also diastole. It has numerous phases.

Phases of the Cardiac Cycle

Isovolumetric ventricular contraction (a-b): This step marks the beginning of systole and also starts through the appearance of the QRS complicated on the EKG and the closure that the AV valves at suggest (a). V all valves closed, the ventricle generates positive pressure without any change in the volume (isovolumetric) to get over the semilunar valves resistance that open at point (b). This phase normally lasts for 6% of the cardiac cycle.Rapid ejection (b-c): as the semilunar valves open up at suggest (b), over there is a fast ejection of blood because of increased ventricular contractility. The arterial pressure rises until reaching its maximum at point (c). This phase generally lasts for 13% the the cardiac cycle.Reduced ejection (c-d): This step marks the start of ventricular repolarization as depicted by the beginning of the T wave on the EKG. Repolarization leads to a rapid decline in ventricular pressures and hence the lessened rate of ejection. However, part forward flow of blood continues an additional to remnant kinetic power from the vault phase. This phase generally lasts for 15% of the cardiac cycle.Isovolumetric relaxation (d-e): when the ventricular pressures drop below the diastolic aortic and pulmonary pressure (80 mmHg and also 10 mmHg respectively), the aortic and also pulmonary valves close producing the second heart sound (point d). This marks the start of diastole. The ventricles generate an adverse pressure without an altering their volume (isovolumetric) so the the ventricular pressure becomes reduced than the atrial pressure. This phase commonly lasts because that 8% the the cardiac cycle.Ventricular pour it until it is full (e-a): as the AV valves open up at allude (e), ventricular filling starts. The initial fast filling is mainly augmented by ventricular suction which outcomes from ventricular untwisting and the return of each ventricular muscle fiber to its slack length. The ventricular pressure gradually increases till it amounts to the atrial pressure and the AV valves nearby (point a). This phase normally lasts for 44% the the cardiac cycle.Atrial contraction: Finally, close to the finish of ventricular diastole, the atrial contraction contributes around 10% the the ventricular pour it until it is full volume. This is stood for by the P wave on the EKG the the following cycle. This phase commonly lasts for 14% that the cardiac cycle.

Heart Sounds

*
regular pressures in miscellaneous chambers of the heart

*
*

The an initial heart sound (S1)represents closure the the atrioventricular (mitral and tricuspid) valves together the ventricular pressures exceed atrial pressures at the start of systole (point a). S1 is usually a single sound due to the fact that mitral and also tricuspid valve closure occurs virtually simultaneously. Clinically, S1 corresponds to the pulse.

The 2nd heart sound (S2) represents closure that the semilunar (aortic and pulmonary) valves (point d). S2 is normally split since the aortic valve (A2) closes before the pulmonary valve (P2). The closing push (the diastolic arterial pressure) ~ above the left is 80 mmHg as compared to just 10 mmHg on the right. This greater closing press leads to previously closure that the aortic valve. In addition, the an ext muscular and also stiff "less compliant" left ventricle (LV) empties previously than the right ventricle. The venous return to the best ventricle (RV) increases throughout inspiration due to an unfavorable intrathoracic pressure and P2 is even much more delayed, so it is typical for the split of the 2nd heart sound to widen during inspiration and also to narrow throughout expiration. Clinically, this is much more remarkable with slow heart rates.

The third heart sound (S3)represents a transition from quick to sluggish ventricular pour it until it is full in beforehand diastole. S3 may be heard in regular children.

The 4th heart sound (S4) is an abnormal so late diastolic sound brought about by forcible atrial contraction in the visibility of diminished ventricular compliance.

*
*

Abnormally large splitting of S2 may take place in:

a) RV volume overload, such as atrial septal defect (ASD) and also anomalous pulmonary venous connection. In these cases, the split is usually vast and "fixed" v no difference in between inspiration and also expiration because of fixed RV volume (see ASD section)

b) RV outflow obstruction, such as pulmonary stenosis (PS)

c) delayed RV depolarization together as finish right bundle branch block

*

Narrow dividing of S2 wake up in:

a) Pulmonary hypertension as the pulmonary valve close the door earlier because of high pulmonary resistance

b) Mild come moderate aortic stenosis as the A2 is delayed

*

Single S2 may occur:

a) If one of the semilunar valves is missing, as in pulmonary or aortic valve atresia and also truncus arteriosus

b) If both valves close at the same time as in pulmonary hypertension with equal pulmonary and also aortic arterial pressures

c) If both valves close concurrently as in double outlet solitary ventricle or in big VSD with equal ventricular pressures

d) Posterior displacement the the pulmonary valve far from the chest wall surface as in d-TGA

Paradoxical separating of S2 (P2 is heard before A2) occurs in:

a) significant aortic stenosis

b) Left bundle branch block

In both conditions, the aortic valve (A2) closes after the pulmonary valve (P2). Because the respiration only affects P2, its result in paradoxical separating is opposing of normal, i.e. Inspiration causes narrow dividing while expiration causes wide splitting that S2.

Heart Murmurs

Murmurs are extr sounds produced by unstable blood circulation in the heart and blood vessels. Murmurs may be systolic, diastolic or continuous.

Grading the systolic mumers based upon thier intensityI/VI: proper audibleII/VI: Faint however easily audibleIII/VI: loud murmur without a palpable thrillIV/VI: loud murmur with a palpable thrillV/VI: really loud murmur heard with stethoscope lightly on chestVI/VI: an extremely loud murmur that have the right to be heard there is no a stethoscope

Systolic murmurs room the many common types of murmurs in children and based on their timing within systole, they space classified into:

a) Systolic ejection murmurs (SEM, crescendo-decrescendo) an outcome from stormy blood flow due to obstruction (actual or relative) throughout the semilunar valves, outflow tracts or arteries. The murmur is heard quickly after S1 (pulse). The soot of the murmur rises as more blood flows throughout an obstruction and then reduce (crescendo-decrescendo or diamond shaped). Chaste murmurs are the many common cause of SEM (see below). Other causes include stenotic lesions (aortic and also pulmonary stenosis, coarctation of the aorta, Tetralogy that Fallot (TOF)) or loved one pulmonary stenosis due to increased circulation from an ASD

*
Crescendo decrescendo murmur

b) Holosystolic (regurgitant) murmurs start at the beginning of S1 (pulse) and continue to S2. Examples: ventricular septal defect (VSD), mitral and also tricuspid valve regurgitation.

*
Holosystolic murmur

c) Decrescendo systolic murmur is a subtype that holosystolic murmur that may be heard in patient with small VSDs. In the latter part of systole, the little VSD might close or end up being so tiny to not enable discernible circulation through and the murmur is no longer audible.

See more: Consider The Following Situation: Percy Is Using Hexagonal Writing Can Help You

*
Decrescendo murmur

Diastolic murmurs room usually abnormal, and may it is in early, mid or late diastolic.