CARDIAC CYCLE

DR RAKESH JAINSR Cardiology

Govt. Medical College, Calicut.

Cardiac Cycle

Def: The cardiac events that occur from beginning of one heart beat to the beginning of the next.

first assembled by Lewis in 1920 but first conceived by Wiggers in 1915

Atria act as PRIMER PUMPS for ventricles & ventricles provide major source of power for moving the blood through the vascular system.

Initiated by spontaneous generation of AP in SA node (located in the superior lateral wall of the right atrium near the opening of the superior vena cava)

Electrical System: Brief

Action potentials originating in the sinus node travel to AV node (1m/s) in 0.03 sec.

1. AV nodal delay of 0.09 sec before the impulse enters the penetrating portion of the A-V bundle2. A final delay of another 0.04 sec occurs mainly in this penetrating A-V bundle total delay in the A-V nodal and A-V bundle system is about 0.13 sec

A total delay of 0.16 sec occurs before the excitatory signal finally reaches the contracting muscle of the ventricles from its origin in sinus node.

Delay in AV node (0.13sec)

Why delay? Diminished numbers of gap junctions Between

successive cells in the conducting pathways.

Significance? Delay allows time for the atria to empty their blood

into the ventricles before ventricular contraction begins

Rapid Transmission in the Purkinje System (1.5 to 4.0 m/sec)

i.e. • About 6x that in ventricular muscle • About 150x that in A-V nodal fibers

allowing almost instantaneous transmission of the cardiac impulse throughout the ventricular muscle

(B/c of very high level of permeability of the gap junctions)

Summary of Cardiac Impulse Transmission

Mechanical Phase

Cardiac cycle – basically describes…

1. Pressure2. Volume, and3. Flow phenomenon in ventricles as a function of time

Basics

1 Beat = 0.8 sec (800 msec) Systole = 0.3 sec Diastole = 0.5 sec In tachycardia, Diastolic phase decreases

more than systolic phase

Phases of cardiac cycle

LV Contraction   Isovolumic contraction (b)

  Maximal ejection (c)LV Relaxation   Start of relaxation and reduced ejection (d)

   Isovolumic relaxation (e)LV Filling   Rapid phase (f)

  Slow filling (diastasis) (g)  Atrial systole or booster (a)

Time Intervals

Total ventricular systole  0.3 sec Isovolumic contraction (b) 0.05 sec (0.015sec for

RV) Maximal ejection (c)  0.1 sec Reduced ejection (d) 0.15 secTotal ventricular diastole 0.5 sec Isovolumic relaxation (e)   0.1 sec Rapid filling phase (f) 0.1 sec Slow filling (diastasis) (g) 0.2 sec Atrial systole or booster (a) 0.1 sec GRAND TOTAL (Syst+Diast) = 0.8 sec

Physiologic Versus Cardiologic Systole and Diastole

PHYSIOLOGIC SYSTOLE

CARDIOLOGIC SYSTOLE

Isovolumic contraction

Maximal ejection

From M1 to A2, including:

Major part of isovolumic contractionMaximal ejectionReduced ejection

PHYSIOLOGIC DIASTOLE

CARDIOLOGIC DIASTOLE

Reduced ejectionIsovolumic relaxationFilling phases

A2-M1 interval (filling phases included)

20msec

Physiological systole

cardiologic systole, demarcated by

heart sounds rather than by physiologic events, starts fractionally later than physiologic systole and ends significantly later.

Cardiologic systole> physiologic systole

Description of Cardiac cycle phases

1. Pressure & Volume events2. ECG correlation3. Heart sounds4. Clinical significance

Atrial SystoleA-V Valves Open; Semilunar Valves Closed

Blood normally flows continually from great veins into atria

80% flows directly thr atria into ventricle before the atria contracts.

20% of filling of ventricles – atrial contraction

Atrial contraction is completed before the ventricle begins to contract.

Atrial contraction normally accounts for about 10%-15% of LV filling at rest, however, At higher heart rates, atrial contraction may account for up to 40% of LV filling referred to as the "atrial kick”

The atrial contribution to ventricular filling varies inversely with duration of ventricular diastole and directly with atrial contractility

Atrial SystolePressures & Volumes

‘ a ‘ wave – atrial contraction, when atrial pressure rises.

Atrial pressure drops when the atria stop contracting.

After atrial contraction is complete LVEDV typically about 120 ml

(preload) End-diastolic pressures of LV = 8-12 mmHg and

RV = 3-6 mmHg AV valves floats upward (pre-

position)

Abnormalities of “a” wave

Elevated a wave Tricuspid stenosis Decreased ventricular compliance (ventricular failure,

pulmonic valve stenosis, or pulmonary hypertension)

Cannon a wave    Atrial-ventricular asynchrony (atria contract against a closed tricuspid

valve) complete heart block, following premature ventricular

contraction, during ventricular tachycardia, with ventricular pacemaker

Absent a wave    Atrial fibrillation or atrial standstill

Atrial flutter

Why blood does not flow back in to SVC/PV while atria contracting, even though no valve in between?

Wave of contraction through the atria moves toward the AV valve thereby having a "milking effect."

Inertial effects of the venous return.

Atrial SystoleECG

p wave – atrial depolarization impulse from SA node results in

depolarization & contraction of atria ( Rt before Lt )

PR segment – isoelectric line as depolarization proceeds to AV node.

This brief pause before contraction allows the ventricles to fill completely with blood.

Atrial SystoleHeart Sounds

S4 (atrial or presystolic gallop) - atrial emptying after forcible atrial contraction.

appears at 0.04 s after the P wave (late diastolic) lasts 0.04-0.10 s Caused by vibration of ventricular wall during

rapid atrium emptying into non compliant ventricle

Causes of S4

Physiological; >60yrs (Recordable, not audible)

Pathological; All causes of concentric LV/RV hypertrophy

Coronary artery disease Acute regurgitant lesionsAn easily audible S4 at any age is generally

abnormal.

Clinical Facts about S4

In contrast to S3, which may mean ventricular failure, the presence of S4 does not indicates heart failure. It only signify “hardworking ventricle”.

The presence of S4 correlate with a gradient of at least 50mmHg across LVOT in suspected LVOT obstruction.

(This correlation is not applicable in HCM)

In setting of MI, an audible S4 indicates that at least 10% of myocardium is at jeopardy.

In presence of Shock, S4 indicates that hypovolemia is unlikely as PCWP will be >18mmHg.

S4 can be heard when RVEDP >12mmHg on Rt or LVEDP > 15mmHg on Lt side. If EDP is very high i.e. >25 mmHg, S4 may be absent b/c of insufficient atrial functions.

JVP: x descent

Prominent x descent    1    Cardiac tamponade

  2    Constrictive pericarditis  3    Right ventricular ischemia with preservation of atrial

contractility

Blunted x descent    1    Atrial fibrillation

  2    Right atrial ischemia

Beginning of Ven.SystoleIsovolumetric ContractionAll Valves Closed

Isovolumetric ContractionPressure & Volume Changes The AV valves close when

the pressure in the ventricles (red) exceeds the pressure in the atria (yellow).

As the ventricles contract isovolumetrically -- their volume does not change (white) -- the pressure inside increases, approaching the pressure in the aorta and pulmonary arteries (green).

JVP: c wave- d/t Right ventricular contraction pushes the tricuspid valve into the atrium and increases atrial pressure, creating a small wave into the jugular vein. It is normally simultaneous with the carotid pulse.

Ventricular chamber geometry changes considerably as the heart becomes more spheroid in shape; circumference increases and atrial base-to-apex length decreases.

Early in this phase, the rate of pressure development becomes maximal. This is referred to as maximal

dP/dt. Ventricular pressure increases rapidly LV ~10mmHg to ~ 80mmHg (~Aortic pressure) RV ~4 mmHg to ~15mmHg (~Pulmonary A pressure)

At this point, semilunar (aortic and pulmonary) valves open against the pressures in the aorta and pulmonary artery

LV Torsion

Figure: Schematic Drawing of LV TorsionThe image on the left shows the myofiber directions. Solid lines epicardial region; dashed lines endocardial region. The image on the right shows untwisting. ED end-diastole; ES end-systole; LV left ventricle.

(J Am Coll Cardiol Img 2009;2:648–55)

left-handed helix in subepicardiumright-handed helix in subendocardium

Isovolumetric ContractionECG

The QRS complex is due to ventricular depolarization, and it marks the beginning of ventricular systole.

Isovolumetric ContractionHeart Sounds

S1 is d/t closure and after vibrations of AV Valves. (M1 occurs with a definite albeit 20 msec delay after the LV-LA pressure crossover.)

S1 is normally split (~0.04 sec) because mitral valve closure precedes tricuspid closure.

(Heard in only 40% of normal individuals)

S1 heart sound

low pitch and relatively long-lasting

lasts ~ 0.12-0.15 sec frequency ~ 30-100 Hz appears 0.02 – 0.04 sec after the

beginning of the QRS complex

Some Clinical facts about S1

S1 is a relatively prolonged, low frequency sound, best heard at apex.

Normally split of S1 (~40%)is heard only at tricuspid area.(As tricuspid component is heard only here.)

If S1 is equal to or higher in intensity than S2 at base, S1 is considered accentuated.

Variable intensity of S1 and jugular venous pulse are highly specific and sensitive in the diagnosis of ventriculoatrial dissociation during VT, and is helpful in distinguishing it from supraventricular tachycardia with aberration.

Value of physical signs in the diagnosis of ventricular tachycardia. C J Garratt, M J Griffith, G Young, N Curzen, S Brecker, A F Rickards and A J Camm, Circulation. 1994;90:3103-3107

Causes of

Loud S1 Soft S1

1. Exercise2. Emotinal excitibility3. Mitral stenosis4. Hyperkinetic circulation5. Atrial septal defect6. Sinus tachycardia7. Short P-R interval

1. Sinus tachycardia2. Mitral regurgitation3. Severe AR4. Ventricular aneurysm5. Acute MI6. Myocarditis7. Cardiomyopathy8. Prolonged P-R interval9. Calcific MS

EjectionAortic and Pulmonic Valves Open; AV Valves Remain Closed

The Semilunar valves ( aortic , pulmonary ) open at the beginning of this phase.

Two Phases• Rapid ejection - 70% of the blood ejected during the first 1/3 of

ejection• Slow ejection - remaining 30% of the blood emptying occurs during the latter 2/3 of ejection

Rapid Ejection Pressure & Volume Changes

When ventricles continue to contract , pressure in ventricles exceed that of in aorta & pul arteries & then semilunar valves open, blood is pumped out of ventricles & Ventricular vol decreases rapidly.

Ventricular contraction: RV v/s LV

Rapid Ejection ECG & Heart Sounds

In rapid ejection part of the ejection phase there no specific ECG changes / heart sounds heard.

Slow EjectionAortic and Pulmonic Valves Open; AV Valves Remain Closed

Blood flow from the left ventricle to the aorta rapidly diminishes but is maintained by aortic recoil, the “Windkessel effect “

At the end of ejection, the semilunar valves close. This marks the end of ventricular systole mechanically.

Slow Ejection ECG & Heart Sounds

T wave – slightly before the end of ventricular contraction

it is d/t ventricular repolarization

heart sounds : none

Beginning of DiastoleIsovolumetric relaxationAll Valves Closed

At the end of systole, ventricular relaxation begins, allowing intraventricular pressures to decrease rapidly (LV from 100mmHg to 20mmHg & RV from 15mmHg to 0mmHg), aortic and pulmonic valves abruptly close (aortic precedes pulmonic) causing the second heart sound (S2)

Valve closure is associated with a small backflow of blood into the ventricles and a characteristic notch (incisura or dicrotic notch) in the aortic and pulmonary artery pressure tracings

After valve closure, the aortic and pulmonary artery pressures rise slightly (dicrotic wave) following by a slow decline in pressure

Isovolumetric relaxation Volumes remain constant because all

valves are closed volume of blood that remains in a

ventricle is called the end-systolic volume (LV ~50ml).

pressure & volume of ventricle are low in this phase .

Isovolumetric relaxation

Throughout this and the previous two phases, the atrium in diastole has been filling with blood on top of the closed AV valve, causing atrial pressure to rise gradually

JVP - "v" wave occurs toward end of ventricular contraction – results from slow flow of blood into atria from veins while AV valves are closed .

Isovolumetric relaxationECG & Heart Sounds

ECG : no deflections

Heart Sounds : S2 is heard when the semilunar vlaves close.

A2 is heard prior to P2 as Aortic valve closes prior to pulmonary valve.

Why A2 occurs prior to P2 ?

“Hangout interval” is longer for pulmonary side (~80msec),compared to aortic side (~30msec).

Hangout interval is the time interval from crossover of pressures (ventricle with their respective vessel) to the actual occurrence of sound.

Due to lower pressure and higher distensibility, pulmonary artery having longer hangout interval causing delayed PV closure and P2.

S2 heart sound

Appears in the terminal period of the T wave

lasts 0.08 – 0.12s

Some clinical facts about S2

Normal split: Two components heard during inspiration and is single sound during expiration.

(A2-P2 ~20- 50 msec in inspiration)

Clinically split is defined as wide, if it is heard well in standing position, in expiration (normally not heard as the split is 15 msec, which can not be heard by human ears)

Single S2: absence of audible split in either phase of respiration.

Fixed split: two components fails to move with respiration.

Reverse split: Inaudible split during inspiration and audible split during expiration. (recognized by wider split in expiration)

Common causes of wide split S2

RBBB Sev PAH ASD Idiopathic dilatation of pul artery Sev right heart failure Moderate to severe PS Severe MR Normal variant

Common causes of wide fixed split S2

ASD All causes of wide split with

associated severe right ventricular failure.

Common causes of single S2

Truncus arteriosus Pulmonary atresia Aortic atresia TGA AS, PS Single loud P2 in extreme PAH

Causes of reverse split S2

LBBB RV pacing RV ectopy Severe AS Acute MI WPW type B Severe TR Aneurysm of ascending aorta Severe systemic hypertension

JVP: V wave

Elevated v wave    1    Tricuspid regurgitation

  2    Right ventricular heart failure  3    Reduced atrial compliance (restrictive myopathy)

a wave equal to v wave    1    Tamponade

  2    Constrictive pericardial disease  3    Hypervolemia

Rapid Inflow ( Rapid Ven. Filling) A-V Valves Open

Once AV valves are open the blood that has accumulated in atria flows into the ventricle.

Rapid Inflow

Volume changes

Despite the inflow of blood from the atria, intraventricular pressure continues to briefly fall because the ventricles are still undergoing relaxation

JVP: Seen as y-descent.

Rapid Inflow ( Rapid Ven. Filling)ECG & Heart Sounds

ECG : no deflections Heart sounds : S3 is heard,

lasts 0.02-0.04 sec (represent tensing of chordae

tendineae and AV ring during ventricular relaxation and filling)

Whatever the mechanism, a sudden inherent limitation in the long axis filling movement of the LV is consistently observed.

Clinical facts about S3

In presence of HF, S3 correlates well with ventricular end diastolic pressure and is usually >25mmHg on left side.

Right sided S3 correlate well with rapid y descend in neck veins.

Normal A2-S3 interval is between 120-160 msec.

Correlates of S3

Anatomical Dilated ventricle

Functional Systolic dysfunction(EF<40%)

Hemodynamics LVEDP Cardiac index Symptoms Doppler flow across AV valve

>25 mmHg<2 L/min/m2

Dyspnea, PND, Orthopnea

Tall E wave compare to A wave

Gallop rhythm

A gallop rhythm is a grouping of three heart sounds that together sound like hoofs of a galloping horse.

Protodiastolic gallop or ventricular gallop or S3 gallop addition of an S3 to the physiological S1 and S2

creates a three-sound sequence, S1-S2-S3. Presystolic gallop rhythm or atrial gallop addition of an S4 to the physiological S1 and S2

creates a three-sound sequence, S4-S1-S2. (during tachycardia S4-S1 can fuse, producing a summation

gallop )

Causes of S3

Physiological: Childrens & young adults <40 yrs (nearly 25%)

(Not heard in normal infants & adult >40 yrs.)

Pathological: Ventricular failure Hyperkinetic state (anemia, thyrotoxicosis, beri-beri) MR, TR AR, PR Systemic AV fistula

JVP: y descent

Prominent y descent    1    Constrictive pericarditis

  2    Restrictive myopathies  3    Tricuspid regurgitation

Blunted y descent    1    Tamponade

  2    Right ventricular ischemia  3    Tricuspid stenosis

DiastasisA-V Valves Open

remaining blood which has accumulated in atria slowly flows into the ventricle.

DiastasisVolume changes

Ventricular volume increases more slowly now. The ventricles continue to fill with blood until they are nearly full.

Diastasis ECG & Heart Sounds

ECG : no deflections Heart Sounds : none

The Lewis or wiggers cycle, Guyton & Hall. Textbook of Medical Physiology, 11th Edition

Volumes

End diastolic vol : During diastole, filling of ventricle increases vol of each ventricle to

~ 110 -120 ml Stroke Vol : amount of blood pumped

out of ventricle during systole. ~ 70 ml End systolic vol : the remaining amount

of blood in ventricle after the systole. ~40 -50 ml

Pressure-Volume Loop

Pressure-volume loop of RV is same as that of LV, however the area is only 1/5th of LV because pressures are so much lower on right

RV v/s LV

Rt Ventricular• Pressure wave 1/5th • dp/dt is less• Isovolumic

contraction & relaxation phases are

short.

Timing of Cardiac EVENTS

1. RA start contracting before LA

2. LV start contracting before RV

3. TV open before MV, so RV filling start before

LV.4. RV peak pressure 1/5th of

LV.5. RV outflow velocity smooth rise & fall, while Lt side

initial peak followed by quick

fall.

The First cardiac catheterization

Cardiac catheterization was first attempted by Dr Werner Forssmann in 1929, at the age of 25 yrs only, when he was a resident in a hospital at Eberswalde, near Berlin. He was his own subject. A fellow resident who agreed to pass the catheter, got scared and abandoned the effort by the time the catheter reached the axilla. Forssmann completed the task himself with radiographer holding the mirror infront of screen. Forssmann catheterize his heart safely nine times till he had no more peripheral veins left to try. But this was not enough to convince the medical world about the safety of the procedure. After being banished from academics, frustrated Forssmann settled for medical practice in a small town.

It was extensive studies with catheterization by Dr Andre Cournand & Dr Dickinson Richard Jr. and eventually the novel prize for physiology & medicine was awarded jointly to Forssmann, Cournand & Richard in 1956.

The history of cardiac catheterization illustrates what reckless idealism of youth can achieve and the long time (here 27 yrs) might take the world to realize the value of even something of great significance.

References

1. Guyton and Hall Textbook of Medical Physiology, 11th Ed. Arthur C. Guyton, John E. Hall.

2. Cardiovascular Physiology Concepts Second Edition, Lippincott Williams & Wilkins, 2011

3. Clinical Methods in Cardiology By Soma Raju, Second Edition, orient longman

4. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, ninth edition

5. Harrison's Principles of Internal Medicine, 19th edition, McGraw-Hill Book Co

6. Understanding Medical Physiology: A Textbook for Medical Students: By R.L. Bijlani, M.D., RL Bijlani MD SM DSc (Hon Causa) FAMS, S. Manjunatha,4th edition

7. Medical Physiology E-Book: By Walter F. Boron, Emile L.Boulpaep, Second Edition

8. Value of physical signs in the diagnosis of ventricular tachycardia. C J Garratt, M J Griffith, G Young, N Curzen, S Brecker, A F Rickards and A J Camm, Circulation. 1994;90:3103-3107

9. Color Atlas of Physiology. Stefan Silbernagel, Agamemnon Despopoulos. 6th Edition.

10. Jacc: cardiovascular imaging, Vol.2 No. 5, 2009. May 2009: 648-55.

QUIZ1. Which letter indicates the point in

the cardiac cycle that the mitral valve opens?

A. AB. BC. CD. D

2. In a normal cardiac cycle , true is

A. RA ejection precedes LA ejection

B. RV contraction starts before LV contraction

C. LV ejection starts before RV ejection

D. Pulmonary valve closes before aortic valve

3. Which letter in the image represents the isovolumic contraction of the left ventricle in the heart?

A. FB. BC. HD. D

2.

4. Which of the following pairs is INCORRECT?

A. P wave: atrial depolarizationB. QRS complex: ventricular depolarizationC. T wave: ventricular repolarizationD. QT interval: Measure of duration of atrial action

potential

5. Isovolumic contraction phase correspond to

A. AV opening to AV Closure

B. MV closure to MV opening

C. MV closure to AV opening

D. AV opening to MV opening

6. Left ventricular end-diastolic volume is:

A. 30-50 mls

B. 50-70 mls

C. 70-120 mls

D. 120-150 mls

7. Prominent y descent in JVP seen in all except    A.    Constrictive pericarditis

  B.    Restrictive cardiomyopathies  C.    Tricuspid regurgitation

D. Cardiac temponade

8. All are true about S3 except A. Right sided S3 correlate well with rapid y descend in neck veins. B. S3 normally heard in normal infants C. S3 usually indicates systolic dysfunction D. S3 correlates well with ventricular end diastolic pressure usually >25mmHg on left side

9. Cardiac apex is palpable during which phase of cardiac cycle

A. Isovolumic contraction phase B. Isovolumic relaxation phase C. Rapid ejection phase D. Atrial systole phase

10. Sensitive & specific sign of ventricularterial dissociation in VT are A. Variable intensity of S1 B. Variable jugular venous pulse C. Both A & B D. None of the above

Answers1. Which letter indicates the point in

the cardiac cycle that the mitral valve opens?

A. AB. BC. CD. D

2. In a normal cardiac cycle , true is

A. RA ejection precedes LA ejection

B. RV contraction starts before LV contraction

C. LV ejection starts before RV ejection

D. Pulmonary valve closes before aortic valve

3. Which letter in the image represents the isovolumic contraction of the left ventricle in the heart?

A. FB. BC. HD. D

2.

4. Which of the following pairs is INCORRECT?

A. P wave: atrial depolarizationB. QRS complex: ventricular depolarizationC. T wave: ventricular repolarizationD. QT interval: Measure of duration of atrial action

potential

5. Isovolumic contraction phase correspond to

A. AV opening to AV Closure

B. MV closure to MV opening

C. MV closure to AV opening

D. AV opening to MV opening

6. Left ventricular end-diastolic volume is:

A. 30-50 mls

B. 50-70 mls

C. 70-120 mls

D. 120-150 mls

7. Prominent y descent in JVP seen in all except    A.    Constrictive pericarditis

  B.    Restrictive cardiomyopathies  C.    Tricuspid regurgitation

D. Cardiac temponade

8. All are true about S3 except A. Right sided S3 correlate well with rapid y descend in neck veins. B. S3 normally heard in normal infants C. S3 usually indicates systolic dysfunction D. S3 correlates well with ventricular end diastolic pressure usually >25mmHg on left side

9. Cardiac apex is palpable during which phase of cardiac cycle

A. Isovolumic contraction phase B. Isovolumic relaxation phase C. Rapid ejection phase D. Atrial systole phase

10. Sensitive & specific sign of ventricularterial dissociation in VT are A. Variable intensity of S1 B. Variable jugular venous pulse C. Both A & B D. None of the above

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