Cardiac cycle

What is the cardiac cycle?

It refers to all events that occur from the beginning of one heartbeat to the beginning of the next.

What is diastole?

The phase of the heartbeat where the heart ventricles are relaxed and fill with blood.

What is systole?

The phase of the heartbeat where the heart ventricles contract and pump blood into the: aorta (LV) and pulmonary artery (RV).

How do you calculate the cardiac cycle time?

Reciprocal of heart beat= 1/72=0.1388 mins/beat= 0.83 secs/beat. Signup and view all the answers

If the heart rate is 72 beats per minute, what is the duration of the cardiac cycle including the systole and diastole?

1/72=0.01388 mins/beat= 0.833 secs/beat. Systole= 0.5, Diastole= 0.3 approx. Signup and view all the answers

What are the stages of the cardiac cycle?

<ol> <li>Filling phase- diastole and atrial systole</li> <li>Isovolumetric contraction- systole</li> <li>Outflow phase- systole/ early diastole</li> <li>Isovolumetric relaxation- diastole</li> </ol> Signup and view all the answers

What happens during the filling phase of the cardiac cycle?

<ol> <li>Passive filling - atria and ventricles relaxed, blood flows from the vena cava and pulmonary veins into the right and left atria and then into the ventricles.</li> <li>Atrial contraction - atrial depolarization (P wave) causes the atria to contract, forcing blood into the ventricles and completing the EDV.</li> </ol> Signup and view all the answers

What happens during the isovolumetric contraction- systole?

<ol> <li>As atrial contraction completes, atrial pressure begins to fall.</li> <li>This reverses the pressure gradient across the AV valves, causing them to close (S1).</li> <li>At this point, ventricular depolarization (QRS complex) is halfway through and the ventricles contract, rapidly building up pressures inside the ventricles.</li> <li>This phase is referred to isovolumetric contraction because no blood is ejected (all valves are closed) and ventricular volume is unchanged.</li> </ol> Signup and view all the answers

What happens during the outflow phase?

<ol> <li>Once the pressure in the ventricles exceeds the pressure in the aorta/pulmonary trunk the aortic and pulmonary valves open, allowing blood to be pumped from the heart into the great arteries.</li> <li>At the end of systole ventricles begin to relax which decreases the pressure in the ventricles compared to in the aorta - the aortic and pulmonary valves close (S2)</li> </ol> Signup and view all the answers

What happens during the isovolumetric diastole?

<ol> <li>At the end of the outflow phase both sets of valves are closed again.</li> <li>Then ventricles begin to relax, reducing the pressure in the pressure in the ventricles so the AV valves open.</li> <li>Ventricles begin to fill with blood and the cycle starts again.</li> </ol> Signup and view all the answers

What does the S1 sound (lub sound) signify?

It is caused by the closure of mitral and tricuspid valves, marks the beginning of systole. Signup and view all the answers

What does the S2 sound (dub) signify in the cardiac cycle?

It is caused by closure of aortic and pulmonary valves, marks the end of systole and beginning of diastole. Signup and view all the answers

What is the physiological splitting of the S2 heart sound?

<ol> <li>During inspiration, the intrathoracic pressure drops, which increases the venous return to the right side of the heart.</li> <li>This increased volume increases right ventricular ejection time during contraction, thus meaning that the pulmonary valve may take longer to shut than the aortic valve.</li> <li>This causes a split in the valve sounds during inspiration.</li> </ol> Signup and view all the answers

What is the S3 sound in the cardiac cycle?

<ol> <li>It is an early diastolic low frequency filling sound which occurs immediately after S2; best heard at the apex.</li> <li>It is related to the acceleration and deceleration of blood during early passive filling of the ventricle.</li> <li>It is referred to as a diastolic murmur in some cases.</li> </ol> Signup and view all the answers

What is the clinical significance of the S3 sound?

<ol> <li>In a healthy child or young adult with no evidence of heart disease, it is physiological and a normal finding.</li> <li>In an older patient with previous history of heart disease, it could be pathological- due to left ventricular dysfunction. They should be referred for an ECG.</li> </ol> Signup and view all the answers

What is the clinical significance of the S2 sound?

If there is a physiological splitting of the S2 sound during inspiration only, it means the finding is physiological- meaning normal. Signup and view all the answers

What is the S4 heart sound?

<ol> <li>It is a late diastolic low frequency filling sound which occurs shortly before S1; best heard at the apex.</li> <li>Due to atrial contraction causing rapid blood flow to a stiff ventricle (decreased compliance)</li> <li>Common causes include MI, hypertension and aortic stenosis (almost always pathological).</li> </ol> Signup and view all the answers

What conditions are the causes for the S4 heart sound?

Myocardial ischaemia, hypertension and aortic stenosis (almost always pathological) Signup and view all the answers

What is the point of auscultation of the aortic valve?

2nd right intercostal space, sternal edge Signup and view all the answers

What is the point of auscultation of the pulmonary valve?

2nd left intercostal space, sternal edge Signup and view all the answers

What is the point of auscultation of the tricuspid valve?

4th left intercostal space, sternal edge Signup and view all the answers

What is the point of auscultation of the mitral valve?

5th left intercostal space, midclavicular line. - Apex beat can be palpated here <ul> <li>Cardiomegaly often shifts the apex beat to the left</li> </ul> Signup and view all the answers

What is the jugular venous pulse?

Stretch and recoil of arteries keep the blood moving forward in diastole and prevent the arterial pressure from falling, despite ventricular pressure being close to 0. Signup and view all the answers

What is the pathway of jugular venous contraction pulsation?

<ol> <li>‘a’ - atrial contraction</li> <li>‘c’ - bulging of tricuspid valve into atrium during ventricular contraction</li> <li>‘v’ - rise of atrial pressure during atrial filling: release as AV valves open</li> </ol> Signup and view all the answers

How do you estimate Jugular venous pulse? What does it indicate?

<ol> <li>A normal JVP is no more than 3 cm vertically above the sternal angle when the patient is lying at a 45 degree angle.</li> <li>The estimation of Jugular venous pressure (JVP) is an indirect estimate of right atrial pressure (central venous pressure).</li> <li>An elevated JVP is one of the sign of heart failure.</li> </ol> Signup and view all the answers