Cardiac cycle ppt (2)

Definition

• Cardiac cycle is defined as the sequence of
coordinated events which take place during
heartbeat.

• Each heartbeat consists of two major
periods called systole and diastole.

• During systole there is contraction of the
cardiac muscle and pumping of blood from

• • During diastole, there is relaxation of cardiac
muscle and filling of blood.
• Various changes occur in different chambers
of heart during each heartbeat.
• These changes are repeated during every
heartbeat in a cyclic manner.

Divisions of cardiac cycle

• The contraction and relaxation of atria are
called atrial systole and atrial diastole
respectively. The contraction and relaxation of
ventricles are called ventricular systole and
ventricular diastole respectively.

• It is named after Dr. Carl J. Wiggers, M.D.
• A Wiggers diagram is a standard diagram used in
cardiac physiology
• The X axis is used to plot time, while the Y axis
contains all of the following on a single grid:
• Blood pressure
Aortic pressure
Ventricular pressure
Atrial pressure
• Ventricular volume
• Electrocardiogram
• Arterial flow (optional)

• The cardiac cycle, fully delineated by Lewis but
first conceived by Wiggers.
• It yields important information on the temporal
sequence of events in the cardiac cycle.
• The three basic events are
(1)LV contraction
(2) LV relaxation
(3) LV filling

Systolic intervals[0.27]
Isometric 0.05
contraction

Ejection period 0.22

Diastolic intervals[0.53]
Proto diastole 0.04
Isometric relaxation 0.08
Rapid filling 0.11
Slow filling 0.19
Atrial systole 0.11

L.v.contraction.
• LV pressure starts to build up when
the arrival of calcium ions at the
contractile proteins starts to trigger
actin-myosin interaction.
• On the electrocardiogram (ECG), the
advance of the wave of
depolarization is indicated by the
peak of the R wave .
• Soon after, LV pressure in the early
contraction phase builds up and
exceeds that in the left atrium .
(normally, 10 to 15 mm Hg).
• followed about 20 milliseconds later
by M1, the mitral component of the
first heart sound.

cardiac cycle
• Mitral valve closure is often thought to coincide
with the crossover point at which the Lvpressure
starts to exceed the left atrial pressure.
• In reality mitral valve closure is delayed because
the valve is kept open by the inertia of the blood
flow.
• Shortly thereafter, pressure changes in the right
ventricle, similar in pattern but lesser in magnitude
to those in the left ventricle, cause the tricuspid
valve to close.there by creatingT1, the second
component of the first heart sound.

cardiac cycle
• During this phase of contraction between
mitralvalve and aortic valve opening, the LV
volume is fixed (isovolumic contraction)
because aortic and mitral valves are shut.
• As more and more myofibers enter the
contracted state, pressure development in the
left ventricle proceeds.
• The interaction of actin and myosin increases
and cross-bridge cycling rises.

cardiac cycle
• When the pressure in the left ventricle
exceeds that in the aorta, the aortic valve
opens, usually a clinically silent event.
• Opening of the aortic valve is followed by the
phase of rapid ejection.
• The rate of ejection is determined not only by
the pressure gradient across the aortic valve,
but also by the elastic properties of the aorta
and the arterial tree, which undergoes systolic
expansion.
• LV pressure rises to a peak and then starts to

• In the 1960s, the duration of isovolumetric
contraction (IVCT) and preejection period
(PEP) were studied extensively as a measure
of cardiac systolic function.

• LV ejection time (LVET) was used as a
measure of LV stroke volume.

• myocardial dysfunction prolongs PEP and
shortens LVET.
• These intervals are also influenced by many
hemodynamic and electrical variables.
• Weissler et al. derived an index (PEP/LVET)
called "systolic time interval“.
• This is less heart rate dependent as a
measure of LV systolic function.

IVCT and IVCTindex in mitral stenosis
• In severe pure or predomnnant mitral stenosis
there is a prolongation in the first component
(C-Mi interval).

• a diminution in the second (Mi-E interval).

• the total IVCT remains practically unaltered.

In Aortic stenosis

• the Q-Mi interval was moderately prolonged
(mean= 66-3 msec).
• It seems possible that left ventricular
hypertrophy may be responsible for the delay
of the intraventricular spread of the electric
stimulus.

• Modification of the elastic properties of the
myocardial fibres in left ventricular
hypertrophy may lead to a delay in the
transformation of the cardiac ovoid into a
sphere.

• hence the preisometric phase of contraction
(Q-Mi) will be prolonged (Warembourg and
Dubar, I967).

LEFT VENTRICULAR RELAXATION.
• As the cytosolic calcium ion concentration
starts to decline because of uptake of calcium
into the SR under the influence of activated
phospholamban, more and more myofibers
enter the state of relaxation and the rate of
ejection of blood from the left ventricle into
the aorta falls. ( phase of reduced ejection)
• During this phase, blood flow from the left
ventricle to the aorta rapidly diminishes but is
maintained by aortic recoil—the Windkessel
effect.

• The pressure in the aorta exceeds the falling
pressure in the left ventricle.
• The aortic valve closes, creating the first
component of the second sound, A2 (the
second component, P2, results from closure of
the pulmonary valve as the pulmonary artery
pressure exceeds that in the right ventricle).
• Thereafter,the ventricle continues to relax.
Because the mitral valve is closed during this
phase, the LVvolume cannot change
(isovolumic relaxation).

• isovolumic relaxation time (IVRT) is also
affected by LV function.
• Mancini et incorporated IVRT into an index
called the "isovolumic index" derived as (IVCT
+ IVRT)/LVET.
• The sum of IVCT and IVRT was measured by
subtracting the LVET from the peak of the R
wave on the electrocardiogram to the onset of
mitral valve opening.

• The isovolumic index was considered more
sensitive for cardiac dysfunction than the
systolic time interval because it contains IVRT
as well as IVCT.

However, the interval from the R wave peak to
the onset of mitral valve opening contains an
interval of electromechanical delay, which can
be pronounced in patients with left bundle
branch block

• With the advent of Doppler echocardiography,
it has become easier to determine cardiac
time intervals more reliably. Tei et al.
proposed a "myocardial performance index"
(or "Tei index") .

• Using Doppler echocardiography to identify
the exact onset of isovolumic contraction.

• Another promising clinical area from
measuring time intervals with TDI is to help
identify patients who might benefit from
cardiac resynchronization therapy.
• This is because TDI can assess the degree of LV
mechanical dyssynergy by precisely
determining the time intervals between peak
systolic contractions of different areas of the
LV wall .

• When the LV pressure
falls to below that in
the leftatrium, the
mitral valve opens
(normally silent) and
the filling phase of the
cardiac cycle restarts.

LEFT VENTRICULAR FILLING PHASES.
• As LV pressure drops below that in the left
atrium, just after mitral valve opening, the
phase of rapid or early filling occurs, which
accounts for most of the ventricular filling.
• Active diastolic relaxation of the ventricle may
also contribute to early filling ( “Ventricular
Suction During Diastole”).
• Such rapid filling may cause the physiological
third heart sound (S3), particularly when there
is a hyperkinetic circulation.

L V FILLING PHASES.
• As pressures in the atrium and ventricle
equalize, LV filling virtually stops (diastasis).
• This is achieved by atrial systole (or the left
atrial booster), which is especially important
when a high cardiac output is required, as
during exercise, or when the LV fails to relax
normally, as in left ventricular hypertrophy.

Definitions of Systole and Diastole
• The start of systole can be
regarded as the beginning
of isovolumic contraction,
when LV pressure exceeds
the atrial pressure, or as
mitral valve closure (M1).
• These correspond
reasonably well, because
mitral valve closure
actually occurs only about
20 milliseconds after the
crossover point of the
pressures.

• Physiological systole lasts from the start of
isovolumic contraction (whenLV pressure crosses
over atrial pressure ) to the peak of the ejection
phase, so that physiological diastole commences as
LV pressure starts to fall .
• Physiological diastole commences as calcium ions
are taken up into the sarcoplasmic reticulum.
• In contrast, cardiological systole is demarcated by
the interval between the first and second heart
sounds, lasting from the first heart sound (M1) to
the closure of the aortic valve(A2).

• The remainder of the cardiac cycle automatically
becomes cardiological diastole. Thus,cardiological
systole, demarcated by heart sounds rather than by
physiological events.
• It starts fractionally later than physiological systole
and ends significantly later.
• For the cardiologist,protodiastole is the early phase
of rapid filling, when the third heart sound (S3) can
be heard.
• This sound probably reflects ventricular wall
vibrations during rapid filling.

Physiological Versus Cardiological
Systole and Diastole

Pressure volume loop in cardiac cycle

Left ventricular rotation: a neglected
aspect of the cardiac cycle
• Rotation of the left ventricle around its
longitudinal axis is an important but thus far
neglected aspect of the cardiac cycle.
• LV rotation during systole maximizes
intracavitary pressures, increases stroke
volume, and minimizes myocardial oxygen
demand.

• Shearing and restoring forces accumulated
during systolic twisting are released during
early diastole and result in diastolic LV
untwisting or recoil promoting early LV filling.

• LV twist and untwist are disturbed in a
number of cardiac diseases and can be
influenced by several therapeutic
interventions by altering preload, afterload,
contractility, heart rate, and/or sympathetic
tone,

L.V and R.v pressure waves
• Right and left ventricular waveforms are
similar in morphology.
• They differ mainly with respect to their
magnitudes.
• The durations of systole and isovolumic
contraction and relaxation are longer and the
ejection period shorter in the left than in the
right ventricle.

GREAT VESSEL PRESSURES.
• The contour of the central aortic and
pulmonary artery pressure tracing consists of
a systolic wave, the incisura (indicating
closure of the semilunar valves), and a
gradual decline in pressure until the
following systole.

Heart sounds in relation to
cardiac cycle

Hemodynamic Correlates of S1

• The first high-frequency component of M1
coincides with the downstroke of the left
atrial c wave and is delayed from the LV–left
atrial pressure crossover by 30 ms.
• Forward flow continues for a short period
following LV–left atrial pressure crossover as a
result of the inertia of mitral flow, with M1
occurring 20 to 40 ms later.

• An even greater delay between the
occurrence of T1 and RV–right atrial pressure
crossover has been shown.
• T1 coincides with the downstroke of the right
atrial c wave.
• These hemodynamic data confirm the prime
role played by the AV valves in the genesis of
S1

The Second Heart Sound
• RV ejection begins prior to LV ejection, has a
longer duration, and terminates after LV
ejection, resulting in P2 normally occurring
after A2.
• the pulmonary artery incisura is delayed
relative to the aortic incisura, primarily a
result of a larger interval separating the
pulmonary artery incisura from the RV
pressure compared with the same left-sided
event.

.
• This interval has been called the hangout
interval, a purely descriptive term coined in
Shaver laboratory more than 30 years ago.
• Its duration is felt to be a reflection of the
impedance of the vascular bed into which the
blood is being received.
• Normally, it is less than 15 ms in the systemic
circulation and only slightly prolongs the LV
ejection time.

• In the low-resistance, high-capacitance
pulmonary bed, however, this interval is
normally much greater than on the left,
varying between 43 and 86 ms.

• Hangout interval contributes significantly to
the duration of ejection.

Normal Physiologic Splitting
• Normally during expiration, A2 and P2 are
separated by an interval of less than 30 ms
and are heard by the clinician as a single
sound
• During inspiration, both components become
distinctly audible as the splitting interval
widens, primarily caused by a delayed P2,
although an earlier A2 contributes to a lesser
degree .

• The absolute value of inspiratory splitting
varies with age and depth of respiration. In
younger subjects, maximal splitting during
inspiration averages 40 to 50 ms.
• with age, this value decreases such that a
single S2 during both phases of respiration can
be normal in subjects older than 40 years of
age.

The Third and Fourth Heart Sounds
• S3 and S4 are low-frequency events related to
early and late diastolic filling of the ventricles .
• When they are heard in disease states, they
are called gallop sounds.
• Their presence gives valuable information to
the clinician regarding the status of ventricular
function and compliance.

• The physiologic S3 is a benign finding
commonly heard in children, adolescents, and
young adults.
• This is a low-frequency sound that follows A2
by 120 to 200 ms and occurs during rapid
filling of the ventricle .
• There are two theories: an external and an
internal production theory.

• In the internal production theory the S3 is due
to a sudden “pullingshort” of the rapidly
expanding ventricle by unknown myocardial
forces at the end of the early rapid expansion
phase.
• In external production theoryAn S3 often
cannot be recorded inside the LV in a patient
in whom it can be recorded externally on the
chest wall .

External production theory
• There is no feature of the LV pressure curve
that consistently corresponds to the S3.

• The apex cardiogram shows a peak of rapid
early outward movementat the time of the S3.

• When marked, this peak is palpable and is
then accompanied by a loud S3.

• Under pathologic conditions, forceful atrial
contraction generates a low-frequency sound
(S4) just prior to S1 .
• Atrial contraction must be present for
production of an S4.
• It is absent in atrial fibrillation and in other
rhythms in which atrial contraction does not
precede ventricular contraction.

Cardiac cycle ppt (2)

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Cardiac cycle ppt (2)