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cardiac cycle lecture
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CARDIAC CYCLEDR RAKESH JAIN
SR CardiologyGovt. 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 cycleLV 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 IntervalsTotal 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 phases1. 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 ofLoud S1 Soft S11. 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 S3Anatomical 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.
References1. Guyton and Hall Textbook of Medical Physiology, 11th
Ed. Arthur C. Guyton, John E. Hall.2. Cardiovascular Physiology Concepts Second Edition,
Lippincott Williams & Wilkins, 20113. Clinical Methods in Cardiology By Soma Raju, Second
Edition, orient longman4. Braunwald's Heart Disease: A Textbook of
Cardiovascular Medicine, ninth edition5. 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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