WINDSOR UNIVERSITY SCHOOL OF MEDICINE

1. WINDSOR UNIVERSITYSCHOOL OF MEDICINE Mechanical Action of the Heart: The Cardiac Cycle Dr.VishalSurender .MD.

2. Learning Objectives After reading this chapter you should be able to: 1. Describe the organization of the cardiovascular system. 2. Describe the sequence of events that occur during one cardiac cycle. Explain how pressures and volumes within the heart chambers change. 3. Describe the pressure – volume loop. 4. List the approximate values for mean pressures found at various stages of the cardiac cycle. 5. Explain how an increase in heart rate would affect various stages of the cardiac cycle. 6. Describe and explain the atrial and central venous pressure waves. 7. Explain the ECG in terms of the cardiac cycle. 8. Describe and explain when sounds are heard during the cardiac cycle. 9. Explain why S2 is split. 10. List and explain the common types of heart murmurs.

3. To understand the Mechanical event you must recall: Anatomy of the Heart • The atrioventricular (AV) valves prevent from flow from the ventricles back into the atria • The pulmonary and aortic valves prevent backflow from the pulmonary trunk into the right ventricle and from the aorta into the left ventricle respectively • Cardiac- muscle cells are joined by gap junctions that permit action potentials to be conducted from cell to cell • The myocardium also contains specialized muscle cells that constitute the conducting system of the heart, initiating the cardiac action potentials and speeding their spread through the heart

4. Cardiac cycle describes the sequence of electrical and mechanical events that occur in the heart during one single beat • The cycle is divided into two major phases, both named for events in the ventricles:the period of ventricular contraction and blood ejection, systole, followed by the period of ventricular relaxation and blood filling, diastole. • At an average heart rate of 72 beats/min, each cardiac cycle lasts approximately 0.8 s, with 0.3 s in systole and 0.5 s in diastole

5. Cardiac valves operation. They open when pressure gradient across the valves is increasing in the direction that blood normally flows (forward pressure gradient) (A). A reverse pressure gradient (B) will force the valve closed, which prevents reverse blood flow in response to reverse pressure gradient that occur as a result of the pumping action. (C). A forward pressure gradient forces the semilunar valve to open. Darker colors correspond to higher pressure

6. Fig. 7. Divisions of the cardiac cycle: (a) systole; (b) diastole

7. Cardiac pressures during phases of cardiac cycle Major difference between the right and left side of the heart is the pressure values: the right side operates at much lower pressures because the pulmonary system is a low resistance circulation.

8. Late diastole: both sets of chambers are relaxed and ventricles fill passively. 1 START Isovolumic ventricular relaxation: as ventricles relax, pressure in ventricles falls, blood flows back into cups of semilunar valves and snaps them closed. 5 Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. 2 Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. 3 Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. 4 Mechanical Events Mechanical events of the cardiac cycle

9. Late diastole: both sets of chambers are relaxed and ventricles fill passively. 1 START Mechanical Events

10. Late diastole: both sets of chambers are relaxed and ventricles fill passively. 1 START Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. 2

11. Late diastole: both sets of chambers are relaxed and ventricles fill passively. 1 START Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. 2 Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. 3

12. Late diastole: both sets of chambers are relaxed and ventricles fill passively. 1 START Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. 2 Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. 3 4

13. Isovolumic ventricular relaxation: as ventricles relax, pressure in ventricles falls, blood flows back into cups of semilunar valves and snaps them closed. Late diastole: both sets of chambers are relaxed and ventricles fill passively. 1 START 5 Atrial systole: atrial contraction forces a small amount of additional blood into ventricles. 2 Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. 3 Ventricular ejection: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected. 4

15. The heart at rest: atrial and ventricular diastole. The atria are filling with blood from the veins, and the ventricles are relaxing – the AV valves between the atria and ventricles open. Blood is flowing by gravity into the ventricles. The relaxing ventricles expand to accommodate the entering blood. At this moment the ventricles are ~ 80 – 90% filled with blood. This is the section to the left of atrial systole on the diagram.

16. 1. Atrial systole and completion of ventricular filling. The generation of an action potential by the SA node results in a wave of depolarization spreading through the atria P wave on the ECG. Atrial muscle contracts (atrial systole) and atrial pressure rises (a wave). A little more blood (10 – 20%), sometimes called the‘atrial kick’ is pushed into the almost full ventricles. However, a small amount of blood is forced backwards into the great veins (there are no oneway valves between the veins and the atria) causing a similar a wave in the central veins (vena cava). This wave can be seen as a pulse in the jugular vein of a person who is semirecumbent with the head and chest elevated ~ 30 degrees . If a pulse is seen higher up the jugular vein in a person who is upright it indicates that the right atrial pressure is higher than normal.

17. End Diastolic Volume, end-systolic volume and stroke volume • The amount of blood in the ventricles just before systole is the end-diastolic volume. The volume remaining after ejection is the end-systolic volume, and the volume ejected is the stroke volume • Pressure changes in the systemic and pulmonary circulation have similar patterns, but the pulmonary pressures are much lower

18. 2. Ventricular systole A. Isovolumetric Contraction The wave of depolarization reaches ventricles and we have the QRS complex on the ECG, which denotes ventricular depolarization. Shortly thereafter the ventricles contract and squeeze the blood upward and towards the base. As soon as the pressure in the ventricles rises above the atrial pressure, the AV valves close causing the first heart sound. Since the aortic and pulmonary valves are already closed each ventricle is now a closed chamber. They continue to contract and because they are closed, the pressure within them rises very steeply (more in the LV than the RV). This is called the isovolumetric contraction phase -c wave in the RA pressure tracing.

19. When Ventricular pressures exceed aortic and pulmonary trunk pressure, the aortic and pulmonary valves open, and V ejection of blood occurs • When the ventricles relax at the beginning of the diastole, the V pressures fall significantly below those in the aorta and pulmonary trunk, and the aortic and pulmonary valves close. Because the AV valves are also still closed, no change in V volume occurs during this isovolumetric ventricular relaxation The vibrations due to closure of the semilunar valves give rise to the second heart sound.

20. When ventricular pressures fall below the pressures in the right and the left atria, the AV valves open, and the ventricular filling phase of diastole begins • Filling occurs very rapidly at first so that atrial contraction, which occurs at the very end of diastole, usually adds only a small amount of additional blood to the ventricles

21. Table of events in the cardiac cycle

22. The Atrial and Central Venous Pressure (CVP) waves • Since there are no valves between the jugular veins (JV), v. cavae ant the RA, the right JV are communicated with the RA. • Changes in pressure in the RA produces a series of pressure changes which are reflected in the central veins and recorded from the JV: a, c and v waves. • CVP is the pressure in the vein at the entrance of the RA • a wave is due to increase in pressure caused by atrial systole • av descent (minimum) is due to relaxation of the right atrium and closure of the tricuspid valve • c wave is caused in the RA by the tricuspid valve bulging back into the atrial chamber as it closes. In the internal JV the c wave (c = carotid) is caused partly by expansions of the carotid artery

23. X descent is a sharp fall in the pressure caused by atrial relaxation • v wave. As the atria fill, A pressure rises producing v wave (v = ventricular systole which is occurring at the same time) • Y descent is a fall in pressure due to the rapid emptying of the atria after the AV valve opens Fig. 13. Jugular venous pressure changes caused by cardiac cycle

24. Clinical examination of the JVP • JP of the internal jugular vein can be assessed by expecting the right side of the neck of a recumbent subject. Two sudden venous collapses (the X and Y descent) should be seen and measured externally on the right side of the neck- positive JVP • Certain cardiac diseases produce characteristic abnormalities in the JVP, e.g. tricuspid incompetence produces exaggerated v waves in the neck, because V systole forces blood back into the RA & JV • In right-side cardiac failure there is also a positive JVP due to accumulation of blood into the failing RV and RA

25. Fig. 8. Pressure-volume loop of the cardiac V at rest and during exercise

26. Fig. 9. Events in the left atrium, left V, and aorta during the cardiac cycle

27. Fig. 10. Pressures in the right ventricle and pulmonary artery during the cardiac cycle. The fig. is done in the same scale as the previous to facilitate comparison

28. Fig.11. Stroke volume. R. Rhodes & R. Pflanzer, Human Physiology

29. Fig. 12. Cardiac cycle again with identification of the jugular venous pulse (a, c and v waves)

30. Heart Sounds. The common heart sound are: • The first heart sound is due to the closing of the AV valves • The second heart sound is due to the closing of the aortic and pulmonary valves

31. Heart Sounds Note that a physiological S3 sound is present in some normal individuals, particularly children. Occurs in early diastole with rapid filling of the ventricles; When present S4 coincides with atrial contraction but usually it is abnormal

32. Location of the sounds on the chest Each valve is best heard by a stethoscope from 4 distinct areas: Mitral valve: Mid clavicular line of the 5th left intercostal space Tricuspid valve: 5th interspace at the left sternal edge Aortic valve: 2nd interspace at the right sternal edge Pulmonary valve: 2nd interspace at the left sternal edge

33. Heart Murmurs: Abnormal heart sounds heard on auscultation which are due to faulty valves. • Incompetence: Failure of the valve to seal properly (valve may be torn, perforated, affected by rheumatic fever or a failing heart may be enlarged) such that it becomes leaky allowing blood to regurgitate through it • Stenosis: The open valve is narrowed so that a higher pressure gradient is needed to drive blood through (cicatrization after rheumatic or other infection) • Defective valves can be congenital or acquired. Abnormal valve causes blood turbulence which sets up high frequency vibrations which are heard as murmurs through the stetoscope

34. Fig. 14. Common valvular abnormalities

35. Heart Murmurs (cont.) • Benign Systolic Murmur is common in the young. Caused by turbulence in the ventricular outflow tract. Also during pregnancy, strenuous exercise and anemi • Aortic stenosis: Systolic murmur. Due to narrowing of the aortic valve when the flow during ejection becomes turbulent. Heard during ejection (systolic murmur) as ejection waxes and wanes (a crescendo – decrescendo murmur). Loudest over aortic area • Mitral incompetence: Pan systolic murmur. During V systole blood regurgitates through the mitral valve back into LA resulting a murmur that extends throughout ventricular contraction

36. Aortic Incompetence: Diastolic murmur When aortic valve does not close completely blood regurgitates back into the V during diastole. The turbulence is upstream of the aortic valve and the murmur begins at the time of S2 and lasts through the early part of diastole • Mitral Stenosis: Diastolic murmur Blood is forced through the narrowed mitral valve during the phase of ventricular filling – ventricular diastole • Listen to these murmurs at various websites e.g. www.med.ucla.edu/wilkes/intro.html

37. Summary of the Cardiac Cycle Assessed at the bedside by noting: • Peripheral pulse at radial artery (heart rate and force) • Systolic and diastolic blood pressure (will be discussed later) • Jugular venous pulse observation • Apex beat (displacement on the left identifies left V hypertrophy) • Heart sounds When pathology is suspected more specialized tests are carried out: • Echocardiography (non-invasive): Observing movement of the valves and walls of the heart (valve lesions, myocardial infarction, cardiac hypertrophy of different origin) • Cardiac catheterization (invasive)

38. Valve positions during the Cardiac cycle

39. Mean Pressures During Cardiac Cycle