Cardiac muscle function. Cardiac Cycle

• Summary:
• ventricular pressure is low
• ventricular volume ↑
• aortic pressure ↓
• ECG - isoline

4. ______________________________

• Point 4. Ventricular pressure has fallen to a level that now is less than left atrial pressure, causing the mitral (AV) valve to open
• The left ventricle fills with blood from the left atrium passively and also actively as a result of atrial contraction in the next cycle
• Left ventricular volume increases back to the end-diastolic volume of 140 mL

2. Ventricular ejection (2 → 3)

• Point 2. _______________________________________, causing the aortic valve to open
• blood is rapidly ejected, driven by the pressure gradient between the left ventricle and the aorta
• left ventricular pressure remains high because the ventricle is still contracting
• ____________________________________
• Point 3. The end-systolic volume, 70 mL
• The width of the pressure-volume loop is the volume of blood ejected, or the stroke volume = 70 mL

Events of Isovolumetric Contraction

• Pressure changes:
• Left ventricular pressure increases dramatically
• the left ventricle contracts
• As soon as left ventricular pressure exceeds left atrial pressure, the mitral valve closes
• In the right heart, the _______________________

• the left ventricle contracts
• Electrical changes:
• The end of this phase coincides with the __________________________________ on the ECG and with the end of ventricular contraction.

1.Electrical change – changes on ECG

2.Mechanical change – Valves open/close

3.Hemodynamic change – Aortic pressure, Atrial pressure, Ventricular pressure, Ventricular volume, Venous pulse change

4.Heart sounds – caused by mechanical and hemodynamic events

• The ventricle keeps filling with blood from the left atrium
• Volume Changes:
• Ventricular volume _________________

• The ventricle can develop greater tension and pressure during systole and eject a larger volume of blood than normal
• Stroke volume increases
• End-systolic volume decreases
• less blood remains in the ventricle at the end of systole
• Summary:

↑ contractility => ↓ ESV => ↑ SV => ↑ EF

• Volume Changes:
• Ventricular volume continues to fall – ________________
• the aortic valve is still open
• blood continues to be ejected from the left ventricle into the aorta

• Pressure changes:
• Left ventricular pressure falls
• because the ventricles are no longer contracting
• Aortic pressure falls
• Even though blood continues to be added to the aorta from the left ventricle, blood is “running off” into the arterial tree at an even faster rate
• Left atrial pressure increases
• blood is returned to the left heart from the pulmonary circulation

In the image the left ventricular pressure-volume loop drawn with the solid line was recorded in a healthy patient at rest (normal). Compared to the normal pressure-volume loop, what cardiovascular parameter is reduced in the pressure-volume loop drawn with the dashed line?

Atrial Sytole

• The ventricle fills with blood from the left atrium
• Volume Changes:
• Ventricular volume increases
• blood is actively ejected from the left atrium to the left ventricle through the open mitral valve
• Reaches

Atrial Systole

• Pressure changes:
• Left atrial pressure increases
• Due to Contraction of the left atrium
• Ventricular pressure remains low
• “blip” in left ventricular pressure reflects this additional volume added to the ventricle from atrial systole
• ___________________________________________________
• blood runs off from the aorta into the arterial tree, to the veins, and then back to the heart.

• Summary:
• Ventricular volume ↓
• Left atrial pressure ↓
• Ventricular pressure ↑
• Aortic pressure ↑

• The ventricle continues to contract, and ventricular pressure reaches its highest value.
• aortic valve opens
• Volume Changes:
• Ventricular volume dramatically decreases
• _______________________________________________, dramatically decreasing ventricular volume

• To increase contractility:
• Sympathetic nervous system activity
• To decrease contractility:

Systole and Diastole pressure volume curves

In the Wiggers diagram below, at which point will sarcomere length of left ventricular myocytes be greatest?

• Heart sounds:
• Inspiration delays closure of the pulmonic valve and causes splitting of the second heart sound
• because the associated decrease in intrathoracic pressure produces an increase in venous return to the right side of the heart

• A 73-year-old man presents with cardiac failure and clinical signs of impaired ability to pump blood forward. Five years ago, he was diagnosed with severe aortic valve stenosis, which chronically increased his cardiac afterload. Three years ago, cardiac ultrasound showed the walls of his left ventricle had thickened all around (concentric hypertrophy). The present ultrasound reveals ventricular walls that are thinner than normal and a dilated left ventricle with a larger volume of blood than normal (eccentric hypertrophy). In the cardiac length-tension curve shown in the image, which of the following combinations best represent the status of his cardiac muscle activity three years ago and at present time?

1. Systole

• Systole is that part of the cardiac cycle in which the heart contracts and blood is ejected.
• In atrial systole, the atria pump blood into the relaxed ventricles
• In ventricular systole, the ventricles pump blood into the blood vessels.
• Blood pressure is greatest during systole and is referred to as the ____________.

3. _____________________________________

• Point 3. Systole ends and the ventricle relaxes.
• Ventricular pressure decreases below aortic pressure and the aortic valve closes.
• Ventricular pressure decreases rapidly during this phase
• Ventricular volume remains constant at the end-systolic value of 70 mL because all valves are closed again.

• Increased preload (↑ blood return to the hart)
• preload is end-diastolic volume
• Preload is increased because venous return is increased, which increases end-diastolic volume (Point 1)
• Afterload and contractility remain constant
• Stroke volume (the width of the pressure-volume loop) increases
• the greater the end-diastolic volume (end-diastolic fiber length), the greater the stroke volume ejected in systole
• Summary:

↑ preload => ↑ EDV => ↑ SV => ↑ EF

A 14-year-old boy is in cardiac arrest after being hit with a baseball in the chest above the left ventricle. This devastating occurrence, called commotio cordis, is very rare, since the impact must occur during the ascending phase of the T wave. Which of the following events is also occurring at this time?

• Jugular venous pulse (JVP):
• Mainly due to the bulging of the tricuspid valve into the atrium (rise in right atrial pressure)
• Occurs near the beginning of ventricular contraction (is coincident with right ventricular isovolumic contraction)
• Is often not seen during the recording of the venous pulse
• __________________________

Events of Ventricular Filling Rapid Ventricular Filling

• When ventricular pressure falls to its lowest level - slightly below left atrial pressure - the
• Electrical changes:
• There is no electrical activity in the heart in this phase (no AP from SA node) – an isoelectric line in the ECG

• Ventricular filling
• Rapid Ventricular Filling
• Reduced Ventricular Filling
• Atrial Systole
• Isovolumetric Ventricular contraction
• Ventricular ejection
• Rapid Ventricular Ejection
• Reduced Ventricular Ejection
• Isovolumetric Ventricular relaxation

__________- The total volume of blood ejected per unit time (mL/min, L/min)

• Depends on the volume ejected on a single beat (stroke volume) and the number of beats per minute (heart rate)

____________= Stroke volume x  Heart rate

Approximately 5000 mL/min  in a 70-kg man

Events of Isovolumetric Relaxation

1.Early ventricular diastole - when T wave ends and the ventricles begin to expand

2.Elastic recoil and expansion would cause pressure to drop rapidly and suck blood into the ventricles

3.filling the ____________________________________

• Isovolumetric ventricular relaxation begins after the ventricles are fully repolarized
• Electrical changes:
• the end of __________________
• the ventricles are fully repolarized

4.‘isovolumetric’ because semilunar valves are closed and AV valves have not yet opened - ventricles are therefore taking in no blood

• Normal Ventricular Pressure-Volume Loop:
• Cardiac cycle = diastole + systole
• The function of the left ventricle can be observed over an entire cardiac cycle  by combining the two pressure-volume relationships from a figure
• By connecting these two pressure-volume curves,

it is possible to construct a ____________________________________

• the systolic pressure-volume relationship shows the maximum

developed ventricular pressure for a given ventricular volume

Reduced Ventricular Ejection

• Heart sounds:

Is described by the following three parameters:

Stroke volume

Ejection fraction

Cardiac output

• Heart sounds:
• No heart sounds

• Heart sounds:
• The first heart sound (S1)
• is caused by the _____________________

Copy -

• Atrioventricular Valves:
• prevent backflow of blood from the ventricles to the atria during systole
• The A-V valves:
• the tricuspid valve - prevents backflow from the right ventricle into the right atrium
• the mitral valve (bicuspid) - prevents backflow from the left ventricle into the left atrium.
• Semilunar valves:
• prevent backflow from the aorta and pulmonary arteries into the ventricles during diastole.
• the aortic valve - separates the left ventricle from the aorta
• the pulmonary artery valve - separates the left ventricle from the aorta
• Principal heart sounds - Reflect valve closure and/or pathologic states:

• Events associated with _____________________:

1.Ventricles expand

2.Ventricular pressure drops below pressure in atria

3.AV valves open and blood flows into the ventricles

4.Reaching the “end-diastolic volume” of ventricles

• Same volume in right and left ventricle - must never be different

• The ventricle begins to fill with blood from the left atrium
• Volume Changes:

• Jugular venous pulse (JVP):
• y descent - Produced by the rapid emptying of the right atrium immediately after the opening of the tricuspid valve
• May be prominent in constrictive pericarditis
• absent in cardiac tamponade. 

• Length-tension relationship for the ventricles:
• The ______________ for the left ventricle is aortic pressure
• Forces resisting flow out of left ventricle
• The higher ______________, the more efforts left ventricle needs to apply to push blood to vessels:
• High blood pressure
• Stiffness of aortic valve
• Hypertrophic cardiomyopathy

• Summary:
• Ventricular volume ↓
• Left atrial pressure ↑
• Ventricular pressure ↓
• Aortic pressure ↓
• ECG – T wave

Events Ventricular Ejection

1.Ejection of blood begins when the ventricular pressure exceeds arterial pressure and forces __________________

2.blood spurts out of each ventricle rapidly at first – rapid ejection

3.then more slowly under reduced pressure – reduced ejection

• stroke volume (SV) of about 70 mL of blood is ejected of the 130-140 mL in each ventricle
• end-systolic volume (ESV) = 60-70 mL of blood left behind

4.ventricular ejections last about 200 – 250 msec

5.corresponds to the plateau phase of the cardiocyte action potential

6.ST segment, T wave 

• Jugular venous pulse (JVP):
• downward displacement of closed tricuspid valve during rapid ventricular ejection phase.
• Reduced or absent in tricuspid regurgitation and right HF because pressure gradients are reduced.

• Jugular venous pulse (JVP):
• a wave
• Highest deflection of the venous pulse
• produced by the contraction of the right atrium
• Correlates with the PR interval
• Is prominent in a stiff ventricle, pulmonic stenosis, and insufficiency
• ________________________
• a wave—atrial contraction

Duration of cardiac cycle

• The total duration of the cardiac cycle, including systole and diastole, is the reciprocal of the heart rate.
• if heart rate is 72 beats/min
• the duration of the cardiac cycle is 1/72 beats/min—about 0.0139 minutes per beat, or 0.833 second per beat.
• atrial systole last about 0.1 sec
• ventricular systole about 0.3 sec
• When _________________________________________________, including the contraction and relaxation phases
• duration of the action potential and the period of contraction (systole) decrease
• At a normal heart rate of 72 beats/min, systole comprises about 0.4 of the entire cardiac cycle.
• At three times the normal heart rate, systole is about 0.65 of the entire cardiac cycle
• As heart rate increases dramatically, the time spent in diastole falls precipitously but the time spent in systole falls to a lesser extent.

1. Isovolumetric contraction (1 → 2)

Begin the cycle at point 1, which marks the end of diastole.

• Point 1. The ______________________________ from the left atrium, its volume is the end-diastolic volume - 140 mL.
• The corresponding pressure is quite low because the ventricular muscle is relaxed
• 1-2. Ventricle is activated, it contracts, ventricular pressure increases dramatically
• all valves are closed
• no blood can be ejected from the left ventricle
• ventricular volume is constant
• Point 2. __________________________________

• A 50-year-old man visits his physician for an annual exam. He complains of mild breathlessness on exertion. Upon cardiac auscultation the physician detects an S3 heart sound. At which point on the cardiac cycle diagram does the S3 heart sound occur?

Jugular venous pulse (JVP)

• The jugular pulse is generated by changes on the right side of the heart.
• This is the indirectly observed pressure over the venous system via visualization of the ____________.
• The pressures will generally vary with the respiratory cycle and are generally read at the end of expiration when intrapleural pressure is at its closest point to zero.

• _______________________, or diastasis, is the longest phase of the cardiac cycle and includes the final portion of ventricular filling, which occurs at a slower rate than in the previous phase.
• Electrical changes:
• There is no electrical activity in the heart in this phase (no AP from SA node) – an isoelectric line in the ECG

• Heart sounds:
• No heart sounds

• Pressure changes:
• Left ventricular pressure falls dramatically
• because the ventricles are relaxed
• When left ventricular pressure falls below aortic pressure, the aortic valve closes
• ____________________________________________________________
• In the point where the aortic valve closes

• Heart sounds:
• The ______________
• is caused by the atrium contracting against, and trying to fill, a stiffened ventricle
• not audible in normal adults, Consider abnormal, regardless of patient age
• c

Length-Tension Relationship in Cardiac Muscle

• The maximal tension that can be developed by a myocardial cell depends on its resting length
• • Depends on the degree of overlap of thick and thin filaments and the number of possible sites for actin-myosin interaction and cross-bridge formation
  • In myocardial cells, ______________________occurs at cell lengths of about ____________, or Lmax - maximal overlap of thick and thin filaments
  • In cardiac muscle also depends on two length-dependent mechanisms:

  1.Increasing muscle length increases the Ca2+ sensitivity of troponin C

  2.Increasing muscle length increases Ca2+ release from the sarcoplasmic reticulum

Diastole:

• Diastole is that part of the cardiac cycle in which the heart relaxes and fills with blood.
• Blood pressure is lowest during diastole and is referred to as the diastolic blood pressure (DBP).
• The ______________ is the difference between the systolic and diastolic pressures.
• A typical value is approximately 40 mm Hg:

• Summary:
• Ventricular volume is constant – end systolic volume
• Ventricular pressure ↓
• Aortic pressure – blip
• S2
• ECG – end of the T wave
• v wave

• Summary:
• Ventricular volume ↑ to the end diastolic volume
• Left atrial pressure ↑
• Ventricular pressure remains low
• Aortic pressure low
• ECG - P wave, PR interval
• a wave

• Jugular venous pulse (JVP):
• Increase in right atrial pressure due to filling ("villing") against dosed tricuspid valve.

At pathologic heart rates ↑ HR =

Events of Ventricular Filling Rapid Ventricular Filling

• Pressure changes:
• Ventricular pressure remains low
• The ventricle is relaxed and compliant
• The ________________________ means that volume can be added to it without changing pressure
• Aortic pressure decreases (is higher than ventricular pressure)
• blood runs off from the aorta into the arterial tree, to the veins, and then back to the heart.
• Left atrial pressure is low

• Heart sounds:
• The ______________
• Produced by rapid flow of blood from the atria to the ventricles
• normal in children but is not heard in normal adults
• the presence of __ indicates volume overload, as in congestive heart failure or advanced mitral or tricuspid regurgitation

• To increase afterload:
• Raise mean blood pressure
• Obstruct outflow of left ventricle (aortic stenosis)
• To decrease afterload:
• Lower he mean blood pressure
• Treat aortic valve disease

• Summary:
• ventricular pressure low
• mitral valve opens
• ventricular volume ↑
• third heart sound
• aortic pressure ↓
• ECG - isoline
• y descent

• Events of Isovolumetric Contraction:

1.Atria repolarize and relax - remain in diastole for the rest of the cardiac cycle

2.Ventricles depolarize

• this initiates the QRS complex
• Depolarization followed by the contraction

3.AV valves close as ventricular blood pressure increases - forcing blood to surge back against the AV cusps

• the left ventricle contracts
• Electrical changes:
• The QRS  complex
• represents the electrical activation – ________________________

• SA node generates AP, it spreads
• Atrial systole is atrial contraction.
• Final phase of ventricular filling
• Electrical changes:
• It is preceded by the P wave
• marks depolarization of the  atria
• PR interval

• The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the ____________.
• Each cycle is initiated by spontaneous generation of an action potential in the sinus node.
• the action potential travels from here rapidly through both atria and then through the A-V bundle into the ventricles
• there is a delay of more than 0.1 second during passage of the cardiac impulse from the atria into the ventricles - allows the atria to contract ahead of ventricular contraction
• The atria act as primer pumps for the ventricles, and the ventricles in turn provide the major source of power for moving blood through the body’s vascular system.

• Ventricular filling occurs in three phases:
• Rapid Ventricular Filling
• blood enters very quickly / before atrial systole begins
• Reduced Ventricular Filling - ___________
• diastole continues in atria
• the longest phase of the cardiac cycle
• marked by slower filling
• Atrial systole
• atria contract

• When left ventricular pressure falls below aortic pressure, the aortic valve closes
• Volume Changes:
• Ventricular volume is constant – end systolic volume
• all valves are closed again, no blood can be ejected from the left ventricle, nor can the left ventricle fill with blood from the atria

A normal electrocardiogram (ECG) trace of one cardiac cycle, and a normal recording of one ventricular action potential, are shown. The wave on the ECG trace marked with a star most closely corresponds to which phase of the ventricular action potential? 

________________

Determinants 4 determinants

Preload: ↑ preload (more stretch of left ventricle) = ↑ CO (more work heart can do)

Afterload: ↑ afterload = more pressure hart must work against = reducing afterload can increase cardiac output, especially in conditions where contractility is impaired

Contractility: an increased contractility of the heart muscle, resulting in ↑ cardiac output

Heart rate: the faster the heart beats, the more blood can be pumped over a particular period of time (despite SV decreases, but if contractility is normal – CO is increased)

• At pathologic heart rates ↑ HR = ↓ CO (high HR with arrhythmia)

• Atrioventricular Valves:
• prevent backflow of blood from the ventricles to the atria during systole
• The A-V valves:
• the tricuspid valve - prevents backflow from the right ventricle into the right atrium
• the mitral valve (bicuspid) - prevents backflow from the left ventricle into the left atrium.
• Semilunar valves:
• prevent backflow from the aorta and pulmonary arteries into the ventricles during diastole.
• the aortic valve - separates the left ventricle from the aorta
• the pulmonary artery valve - separates the left ventricle from the aorta
• Principal heart sounds - Reflect valve closure and/or pathologic states:

• To increase preload:
• Add volume (blood, IVF)
• Slow heart rate -> less frequent contraction -> more time to fill left ventricle
• Constrict veins -> veins force blood into heart -> they hold large blood volume -> in case of blood loss – sympathetic activation -> a1 receptors in veins activated -> venoconstriction -> more blood to heart -> more preload
• To decrease preload:
• Remove volume
• Raise heart rate
• Pool blood in veins (drugs – nitrates)

_________________________________

• Pressure changes:
• Ventricular pressure remains low
• Aortic pressure remains low (is higher than ventricular pressure)
• Left atrial pressure is low

Left Intraventricular pressure

Left ventricular volume

• Ventricular pressure-volume loops can be used to visualize the effects of changes:
• in preload - changes in venous return or end-diastolic volume
• changes in afterload - changes in aortic pressure
• changes in contractility

• The ventricle continues to contract, and ventricular pressure reaches its highest value.
• Pressure changes:
• Left ventricular pressure increases
• the left ventricle contracts
• blood is rapidly ejected from the left ventricle into the aorta through the open aortic valve, driven by the pressure gradient between the left ventricle and the aorta
• Aortic pressure increases
• as a result of the large volume of blood that is suddenly added to the aorta
• Left atrial pressure slowly decreases
• blood is returned to the left heart from the pulmonary circulation

• _________________________________
• afterload is aortic pressure
• The left ventricle must eject blood against a greater-than-normal pressure
• Ventricular pressure must rise to a greater-than-normal level during isovolumetric contraction (point 2) and during ventricular ejection (2 → 3)
• Stroke volume decreases
• End-systolic volume increases
• More blood remains in the ventricle at the end of systole
• Summary:

↑ afterload => ↑ ESV => ↓ SV => ↓ EF

Events of Isovolumetric Contraction

• Volume Changes:
• Ventricular volume remains constant – end diastolic volume
• all valves are closed -  ________________ in response to increase in the ventricular pressure
• the aortic valve has remained closed from the previous cycle

• At what point in the Wiggers diagram below does the QRS complex begin?

• Summary:
• Ventricular volume ↔ - end diastolic volume
• Ventricular pressure ↑↑
• Aortic pressure ↔
• S1
• ECG – QRS complex
• c wave

• _______________________________________
• a portion of the systolic pressure-volume curve is  superimposed as a dashed line on the ventricular pressure-volume loop
• shows the maximum possible pressure that can be developed for a given ventricular volume during systole
• Point 3 on the pressure-volume loop touches the systolic pressure-volume curve
• the portion of the loop between points 4 and 1 corresponds to a portion of the diastolic pressure-volume curve

• The figure shows the aortic pressure, left ventricular pressure, and left atrial pressure during one cardiac cycle. Which of the following sets of data most closely corresponds to the figure above?

During a semiannual exam, the electrocardiogram (ECG) recording of a trained athlete reveals a cardiac arrhythmia shown in the following trace. The abnormality seen in this lead II trace is due to a change in which of the following electrical event(s) in the heart? 

• During reduced ventricular ejection, the ventricles begin to repolarize
• Electrical changes:
• the ventricles begin to repolarize