Cardiac Cycle and Heart SoundsPart I

Mary Beth Fontana

Block Objectives

• Diagram the cardiac cycle, relating electrical and mechanical events to chamber and great artery pressures and ventricular volume; identify systole and diastole

• Describe the mechanism of production of normal and abnormal heart sounds: relate them to the electrical and pressure events of the cardiac cycle

Objectives

• Describe the use of the stethoscope– Auscultatory areas– Use of bell and diaphagm– Interpret the meaning of the auscultatory

findings

Resources• Lilly 5th edition Chapter 2 pp. 28-36,

Table 2.2 P. 42• Blaufuss.org. – heart sound tutorial quiz• There will be auscultation practice

sessions in week 7• The Blaufuss Sound Builder program used

in the practice sessions is available in the App store for a fee

Always Keep In Mind---

• The history and physical examination of the cardiovascular system make the vast majority of the diagnoses!!!!!!!

Auscultation Requires…….

• A quiet environment• A stethoscope with a bell for low pitched

sounds and diaphragm for high pitched sounds, well fitting ear pieces and short tubing 

• A thinking auscultator who-– knows where to place the stethoscope to hear

specific sounds-based on anatomic relationships of the heart and great vessels to chest wall landmarks

•  

Auscultatory Areas

Auscultatory Areas

Aortic Pulmonic

MitralTricuspidAortic 2nd ICS RSB

Pulmonic 2nd ICS LSB

Tricuspid LLSB

Mitral Apex 5th ICS MCL

A Thinking Auscultor

– Can describe the events in the cardiac cycle responsible for the production of the normal and abnormal heart sounds.

– can reproduce the diagram below relating electrical events, mechanical events and heart sounds. This cardiac cycle diagram will be the reference for the discussion of all of the heart sounds.

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Cardiac Cycle

Chamber and Arterial Pressures

Electrical activation causes chamber contraction which raises pressure. Chamber relaxation and emptying cause pressure to fall

ECG

Generation of Heart Sounds• The opening and closing of the heart valves

are determined by pressure differences between the chambers and great vessels on either side of the valves

• Most of the heart sounds discussed in these 2 lectures are related to opening and closing of the cardiac valves

• The sounds occur when the valve leaflets, vessel or ventricular walls tense when they stop moving

Normal Heart Sounds

• First Heart Sound (S1) occurs when the mitral and tricuspid valves close

• Second Heart Sound occurs when the aortic and pulmonic valves close

• Opening of normal cardiac valves is silent

Descriptors of Heart Sounds

• Intensity or loudness• Frequency (high pitched or low pitched)• Splitting– clinically important for the

second heart sound

Intensity Depends Upon…..

• Mobility of the valve leaflets• The distance the leaflets move• The rate of pressure generation driving the

leaflet movement• Mass of the valve leaflets• Source to stethoscope distance

Cardiac Cycle

Chamber and Arterial Pressures

Left heart pressures and velocities are higher than in the right heart, so the contributions to S1 and S2 are louder, higher in frequency

ECG

LV 140/12

Ao 140/90

RV 30/8

PA 30/10

LA (12)

RA (8)

Mitral valve closes

Tricuspid valve closes

First Heart Sound S1

Ventricular depolarization causes ventricular contraction. S1 occurs when ventricular pressure exceeds atrial pressure. Mitral closes before tricuspid

S1LLSB and Apex with the diaphragm

Increased First Heart Sound

• Short PR interval• High cardiac output or tachycardia• Mobile valve leaflets with increased mass

– Scarred stenotic mitral valve– Redundant prolapsing mitral valve

Decreased First Heart Sound

• Long PR interval• Mitral regurgitation– murmur obscures S1,

lack of leaflet coaptation, slow closing velocity

• Decreased leaflet mobility from scarring, calcification– atrioventricular valve stenosis

• Noncompliant LV – high diastolic pressure “precloses” leaflets

Second Heart Sound S2

Aortic valve closes A2

Pulmonic valve closes P2

S1 S2

LV and RV pressures drop below aortic and PA pressures after ejection and relaxation. A2 is louder, best at 2RSB; normal P2 only heard at 2LSB

Increased A2, P2

• Arterial hypertension• Mobile leaflets with increased mass• Increased pulmonary blood flow (P2)

Decreased A2,P2

• Decrease mobility in severe valve stenosis• Calcification of aortic valve may restrict

mobility so severely that A2 is absent

Normal Splitting of S2

• A2 and P2 normally superimposed in expiration

• Inspiration delays P2 due to…..– Negative intrathoracic pressure increases

right heart filling. The RV takes longer to eject the increased volume

– Negative intrathoracic pressure increases pulmonary capacitance, delaying the back flow to close the pulmonic valve

Abnormal Splitting of S2

• Widened splitting – electrical or mechanical delay of the RV delays P2. Split S2 in expiration widens with inspiration

• Fixed splitting – atrial septal defect continuously increases right heart filling, delaying P2, unaffected by respiration

• Paradoxical splitting – electrical or mechanical delay in LV delays A2 so it follows P2. P2 moves out to meet A2 with inspiration

Cardiac Cycle and Heart Sounds Part II

Mary Beth Fontana

Extra Systolic Heart Sounds

Ejection Clicks

Aortic valve opens

Pulmonic valve opens

Audible opening of mobile congenitally stenotic aortic or pulmonic valves, also dilated aorta or PA

S1EC

Follows S1 by duration of isovolumic contraction

High pitched, best at LSB

S2

Nonejection Clicks

S1 A2SC Prolapsing mitral or tricuspid valve leaflets reach limit of motion and tense later in systole

Extra Diastolic Heart Sounds

Opening Snaps

Mitral valve opens

Tricuspid valve opens

Audible opening of mobile stenotic mitral or tricuspid valves; high pitched at LLSB or apex

Ventricular pressure drops below atrial pressure

S1

S2

OS

Third Heart Sound S3

LV early diastolic filling S3

RV early diastolic filling S3

S1

S2

S3

Early diastole after S2. Low pitched-with the bell, left lateral decubitus

Dilated ventricle with poor function and/or increased early diastolic filling

Fourth Heart Sound S4

Atrial contraction S4

S4S1

S2Atrial contraction empties blood into a noncompliant ventricle

In late diastole before S1. Low pitched with the bell LLSB, apex

Summary of Heart Sounds

S4 S1

EC

SC A2

P2

OS

S3