4 - Cardiac Cycle Flashcards
SA Node
AV Node
SA - Naturaly pacemaker, determined rate of spontaneous generation of APs
AV - Only pathway which wave of depolarizations reach ventricles–Slows conduction time intentionally
Why does the R/L heart operate simultaneously?
From a functional standpoint, how should we view the heart?
It has a single electrical conduction system
Two separate pumps in-series
Ventricles vs Atria
Ventricles = Thick walled, pump blood (systemic)
Atria = Thin walled, collect returning venous blood, weak primer pump–increases ~ 40% ventricle filling during exercise
What are the implicatiosn of the in-series arrangement of the heart’s pumps?
- Separation of Pulmonar/Systemic Circulation
- Equal volume of blood from R/L sides
- Left heart generates more pressure
How do Cardiac Valves open and close?
Passively
Cardiac Valves: Atrioventricular (AV) Valves
Prevent backglow of blood into the atria during ventricular systole
Two:
- Tricuspid Valve (Right Atrium - Right Ventricle)
- Mitral Valve (Left Atrium - Left Ventricle)
Cardiac Valves: Semilunar Valves
Prevent backflow of blood from aorta and pulmonary arteries into the ventricles during ventricular diastole
Two:
- Aortic Valve (Left Ventricle - Aorta)
- Pulmonary Valve (Right Ventricle - Pulmonary Artery)
**These valves close fast due to higher pressure, and blood flows through at a greater velocity–smaller openings**
What creates the heart sounds audible with a stethoscope?
Closure of Valves
Normal Heart Sounds: First Heart Sound
Atrioventricular Valves - Closure at Onset of Systole
Normal Heart Sounds: Second Heart Sound
Semilunar Valves - Closure at End of Ventricular Systole
What is the cardiac cycle a measure of?
What measures electrical events during this?
What measures Pressure?
What measures volume?
What measures sounds?
One complete sequence of cardiac contraction and relaxation.
Electrocardiography
Pressure recording devices implanted
Echocardiography (volume)
Phonocardiogram
Ventricular Systole
Period of Ventricular Contraction
Phase 2,3,4
Isovolumetric Contraction
Rapid Ejection
Reduced Ejection
Ventricular Diastole
Period of Ventricular Relaxation
Phase: 5, 6, 7, 1
Isovolumetric relacation
rapid ventricular filling
reduced ventricular filling
Atrial systole
Atrial Systole
Initiation?
Propogation?
Initiated: Spread of action potential through atrium, causes P-wave of ECG
Causes transient rise (“a” wave) in Left Atrial Pressure (LAP)
Atrial Systole: Modulation
Rest/Exercise
Sympathetic Stimulation
At rest, atrial systole accounts for small fractionof ventricular filling
At exercise, atrial systole accounts for greater fraction of ventricular filling (less time available for passive filling due to increased HR)
Sympathetic Stimulation increases contribution of atrial systole to ventricular filling y increasing force of atrial contraction
Atrial Systole (Phase 1)
Blood Volume / EDV
Blood volume within ventricles greatest–End Diastolic Volume (EDV)
Isovolumic Contraction (Phase 2)
ECG
Ventricular Contraction and Valves
ECG: Spreat of AP through Ventricles generates QRS Complex of ECG and initiates ventricular contraction
Ventricular Contraction causes rapid increas in intraventricular pressure; once this exceeds atrial pressure, AV Valves Close (FIRST HEART SOUND S1)
What prevents AV valves from being forced into the atria during ventricular contraction?
They ar acnhored to the papillary muscles by chordae tendineae
When are the ventricles considered Isovolumetric (closed) Chambers?
The interval vetween closure of AV valves and opening of semilunar valves
No Change in Volume–no blood enters or leaves
Rapid Ejection (Phase 3)
Volume Change?
Pressure Change?
When pressures in L/R Ventricles exceed the pressures w/in aorta/pulmonary artery, valves open and blood ejected from ventricles
Volume decrease
- - -
Pressure increase, blood flow peaks
Rapid Ejection (Phase 3)
Atrial Volume Change?
Atrial volume increases because AV valves are closed and venous return is onling
Reduced Ejection (Phase 4)
EKG?
Atrial Pressure?
Ventricular Tension?
Valves?
EKG: T Wave
- - -
Atrial Pressure gradually rises, due to continuous venous return
Ventricular tension decreases, pressure declines, ejection of blood slows (30% blood leaves this stage)
- - -
Slow of flow and reduced pressure cause backflow form Aorta/Pulmonary A. = Semilunar Valves CLOSE = Start of diastole (Second Heart Sound - S2)
What signals the start of diastole?
Dicrotic Notch?
Closure of the Semilunar Valves
- - -
Slight upward deflection in the pressure tracing that interrupts the decline in blood pressure; used to mark end of Ventricular Systole
Isovolumetric Relaxation (Phase 5)
Ventricle vs Aorta Pressure/Volume
Valves
End Systolic Volume
Ventricles Relax, Pressure Drops Rapid
Aorta pressure is more gradual–resitance to blood flow, elastic recoil of vessels
- - -
Volume of Ventricles is constant, AV / Semilunar Valves both closed
End Systolic Volume is volume of blood remaining in ventricles after ventricular contraction
Rapid Filling (Phase 6)
Valves
Cause for Rapid?
Pressure within relaxing ventricles falls below atrial pressure, AV Valves Open, ventricular filling ensues
Rapid because atria are already full from venous return, AV Valve resistance is very low
Rapid Filling (Phase 6)
Ventricular Volume
Ventricular Filling
Volume = dramatic increase
Filling = passive (also during Phase 7)
Reduced Filling (Diastasis, Phase 7)
Passive filling plateaus
Ventricles become less compliant as they fill
(Pressure starts to increase)
Aortic Pressure/Pulmonary Pressure begin to fall
Atrial Systole (Phase 1)
Tops off ventricular volume
Heart Sounds: First Hear Sound (S1)?
Can you detect closure of mitral / tricuspid valves?
Produced by closure of the atriovenricular valves at the onset of ventricular systole
No, usually not distinguishable because they are separated by 0.01 sec
Heart Sounds: Second Heart Sound (S2)
Closure of valves with breathing?
Produced by closure of semilunar valves and end of ventricular systole
Closure of Aortic usually before Pulmonic;
Fused @ Expiration
Separate @ Inspiration (Physiological Splitting of S2)
Clinical: Stenotic Semilunar Valve and Heart Sounds?
Opening of semilunar valves at start of systole usually makes not sound
Stenotic Valve can cause an ejection murmur
Heart Sounds: Third Heart Sound (S3)
Clinical?
When detected, usually early diastole, during passive filling of ventricle–caused by blood hitting ventricular wall
Clinical: Normal in young person, sign of heart failure > 40
Heart Sounds: Fourth Heart Sound (S4)
Contraction of the atria during late diastole
Associated with resistance to filling (impaired relaxation); sign of diastolic heart failure
Murmur
Causes?
Sounds generated by turbulent blood flow
Stenosis - Narrowing of valve; blood flows at higher velocity
Regurgitation - Backflow of blood through a valve
Clinical: Aortic/Pulmonary Stenosis
Clinical: Aortic/Pulmonary Insufficiency
Timing of murmur?
Aortic/Pulmonary Stenosis = Systolic
Aortic/Pulmonary Insufficiency = Diastolic
Clinical: Mitral/Tricuspid Stenosis
Clinical: Mitral/Tricuspid Insufficiency
Timing of Murmur?
Clinical: Mitral/Tricuspid Stenosis = Diastolic
Clinical: Mitral/Tricuspid Insufficiency = Systolic
Bruits
Sounds created by turbulent blood flow
Jugular Venous Pulse Waves
There are no valves from right internal jugular to right atrium
Clinician can judge pressure of right atrium by observing distention of internal jugular vein (caused by retrograde flow of blood)
Normal Jugular Pulse: A Wave
Right Atrial Contraction
Atrial Systole
Normal Jugular Pulse: X Descent
Atrial Relacation (pressure decline)
Normal Jugular Pulse: C Wave
Tricuspid Close; Isovolumetric Ventri_c_ular _C_ontraction
Normal Jugular Pulse: V Wave
Filling of right atrium behind closed Tricuspid
Venous Collection
Normal Jugular Pulse: Y Descent
End of Isovolumetric Relaxation; tricuspid opens
Clincial: Implications of Reduced Duration of Diastole During Tachycardia?
Less time for venous return; tends to reduce cardiac output
Less effective blood flow through coronaries to supply heart myocardia
