2.1 Cardiac Physiology and Conduction Review

Question 1

How Blood Flows Through Heart

Answer 1

Arteries - Blood flows from the heart
Veins - Blood flows too the heart

Superior Vena Cava - Receives deoxygenated blood from upper half of body
Inferior Vena Cava - Receives deoxygenated blood from the lower half of body

1. Right Atrium - Receives deoxygenated blood from the vena cava
2. Blood goes from right atrium, through tricuspid valve into right ventricle
3. Blood exits right ventricle through pulmonary valve to the pulmonary artery (and to the lungs)
4. Blood comes back from lungs through pulmonary veins into the Left Atrium
5. Blood goes from left atrium through Mitral/Bicuspid Valve into the left ventricle
6. Blood goes from left ventricle through the aortic valve to the aorta
7. Aorta pumps blood to the rest of the body.

Question 2

Heart Layers

Answer 2

Pericardium - Sack around the heart that prevents heart from overfilling. It is fibrous and does not have a lot of give, but if the heart enlarges over time, the sac will stretch to accommodate. Issues arise when the pericardium cannot expand enough to keep up with expanding heart (acute phase)

Endocardium - Inner lining of heart

Myocardium - Major muscle mass of heart

Epicardium - Outer surface of heart

Question 3

Coronary Arteries

Answer 3

• Lie on the exterior surface of the heart
• They only fill during diastole
• Anything that lengthens diastole, promotes filling of coronary arteries (coronary perfusion)
  (BETABLOCKERS)

FUNCTION
- Heart receives its own blood supply from the coronary arteries

MAJOR CORONARY ARTERIES
- Left Main Coronary Artery
- Left Anterior Descending Artery (LAD)
- Left Circumflex
- Right Coronary Artery (RCA)

The major coronary artery is the “Left Main”. Occlusion of this artery is called the “widow maker” in acute MI’s.

Right Coronary Artery - Supplies blood to right side of heart and interior surface of heart

Question 4

Heart 2 Systems

Answer 4

• Electrical Conduction System
• Two-Part Pump

ONE CANNOT WORK WITHOUT THE OTHER

Question 5

Electrical Conduction System

Answer 5

• Action potentials start in the SA node (located towards the top of the atria)
• These potentials cause the Atria to contract
• The potentials slow down when they pass the AV node (located between the atria and ventricles)

SA NODE
- Inherent pacemaker of the heart (60-100 bpm)
- Normal heart rhythm is called SINUS RHYTHM

Question 6

Dysrhythmias/Arrhythmias

Answer 6

Dysrhythmias
- Disorder of formation or conduction of electrical impulses in the heart
- Dysfunctional rhythm or abnormal rhythm

Arrhythmias
- Without rhythm

• Disturbances that can affect rate, rhythm or both.

CONCERNS
- Alters blood flow and causes hemodynamic change

DIAGNOSIS
- Analysis of electrographic waveform (ECG)

PROMPT ASSESSMENT OF DYSRHYTHMIA AND PATIENTS RESPONSE TO THE RHYTHM IS CRITICAL
- MOST IMPORTANT TO LOOK AT PATIENT AND TREAT PATIENT

Question 7

CO/HR

Answer 7

Cardiac Output
- Represents the efficiency of the heart
- Volume of blood ejected by the left ventricle each minute
- Determined by HR and STROKE VOLUME

Heart Rate
- Number of heartbeats in a minute

Stroke Volume
- Volume of blood ejected by the left ventricle in one heartbeat

Cardiac Output
HR x Stroke Volume = CO

ANYTHING THAT AFFECTS YOUR HEARTRATE ALSO AFFECTS YOUR STROKE VOLUME

Question 8

Dysrhythmia Causes

Answer 8

• Damage to the electrical conduction system
• Change in conduction cycle (movement of sodium, calcium or potassium)
• Calcium is very important in the SA and AV node. It is required for the heart to contract.
  Anything that damages the heart itself can also damage the conduction system

Question 9

Dysrhythmias

Answer 9

Causes
- Problems with formation of impulses
- Problems with conduction of impulses

Question 10

Automaticity

Answer 10

• Unique quality of cardiac cells (they can generate their own impulses)

If SA node is not firing off properly, other heart muscles can take over because they also have automaticity
- Each cardiac cell has an inherent rate that they can trigger to promote survival of cardiac cells

• Disturbances in the conduction of impulses is called BLOCK which can occur anywhere in the atrial/ventricular area.

Question 11

Antidysrhytmics

Answer 11

Class 1 - Act on Phase 0 of Action Potential
Class 2 - Acts on Phase 2 of Action Potential
Class 3 - Acts on Phase 3 of Action Potential

Question 12

What can Alter the Heart

Answer 12

• Hypoxia, electrolyte imbalances, cardiac surgery, decreased blood flow, acute MI, antidysrhythmic drugs can alter heart rhythm

Question 13

Automaticity

Answer 13

• Heart cells can discharge electrical impulses without external stimuli

SA Node - 60-100 bpm
AV Node - 40-60 bpm
Bundles/Purkinje Fibers - 20-40 bpm

Question 14

Changes in Heart Rate

Answer 14

Sympathetic Influences - Increases HR, AV node conduction, and irritability (less stable and more prone to going their own way when it comes to automaticity). Influences both atria and ventricles.

Parasympathetic Influences - Decreases HR, AV node conduction, and irritability. Only affects the atria, not the ventricles.