4 - Cardiac Cycle Flashcards by John Castillo

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

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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

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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

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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

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How do Cardiac Valves open and close?

Passively

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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)

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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**

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What creates the heart sounds audible with a stethoscope?

Closure of Valves

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Normal Heart Sounds: First Heart Sound

Atrioventricular Valves - Closure at Onset of Systole

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Normal Heart Sounds: Second Heart Sound

Semilunar Valves - Closure at End of Ventricular Systole

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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

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Ventricular Systole

Period of Ventricular Contraction

Phase 2,3,4

Isovolumetric Contraction

Rapid Ejection

Reduced Ejection

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Ventricular Diastole

Period of Ventricular Relaxation

Phase: 5, 6, 7, 1

Isovolumetric relacation

rapid ventricular filling

reduced ventricular filling

Atrial systole

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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)

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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

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Atrial Systole (Phase 1)

Blood Volume / EDV

Blood volume within ventricles greatest–End Diastolic Volume (EDV)

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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)

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What prevents AV valves from being forced into the atria during ventricular contraction?

They ar acnhored to the papillary muscles by chordae tendineae

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When are the ventricles considered Isovolumetric (closed) Chambers?

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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?

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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?

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Atrial volume increases because AV valves are closed and venous return is onling

Reduced Ejection (Phase 4)

EKG?

Atrial Pressure?

Ventricular Tension?

Valves?

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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?

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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

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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** ## Footnote ****_A_**trial 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 **_V_**enous 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

4 - Cardiac Cycle Flashcards

(45 cards)