Ch. 48 Cardiopulmonary Procedures

SA Node

The sinoatrial (SA) node, or the pacemaker, is present in the upper back wall of the right atrium at the junction of the superior vena cava and the right atrium. It is the main component of electrical conduction system of the heart and generates the impulses.

AV Node

The atrioventricular (AV) node is present in the posterior, superior portion of the right atrial septal wall.

Purkinje fibers

The right and left branches of the bundle of His divide into smaller branches, which end in the Purkinje fibers, spreading across the apex of the heart and through the myocardium, thereby stimulating ventricular contraction.

Bundle of His

This is a special group of conduction fibers located in the upper part of the interventricular septal wall.

Systole

the atria and ventricles contract, pushing the blood into the arterial system.

Diastole

the relaxation phase of the heart, the chambers refill with blood from the vascular system and the lungs.

Electrocardiogram (ECG)

records the intensity of the electrical conductive impulses. It also records the actual time taken for each part of the cardiac cycle to occur.

Normal sinus rhythm (NSR)

the duration of each cardiac cycle is the same and each cycle occurs after exactly the same interval of time.

Sinus arrhythmia

Sinus arrhythmias occur due to firing of the sinoatrial node too slowly or quickly

Atrial arrhythmia

• occur due to faulty electrical impulse formation or conduction defects within the atria.

• Premature atrial contraction (PAC) is a type of atrial arrhythmia common in smokers and people who consume large amounts of caffeine.

Ventricular arrhythmia

• Premature ventricular contraction (PVC) occurs due to contraction of ventricles before the need to contract for the next cardiac cycle.

• Ventricular fibrillation occurs when the heart muscle quivers with ineffective pumping of the blood; this is an emergent condition and can quickly result in death.

Biochemical arrhythmia

• Digitalis is effective in slowing and strengthening the heartbeat. However, its overuse may cause toxicity and cardiac arrhythmias.

• Blood pressure medications may cause cardiac arrhythmias.

• Electrolyte imbalance such as altered potassium and sodium levels may impair cardiac function.

Polarization

the resting state of the myocardium. In polarization state, no electrical activity occurs and the myocardial cells get ready for stimulation.

Depolarization

the electrical system of the heart activates the myocardial cells, resulting in the contraction of the stimulated heart muscle.

P wave

Signifies the beginning of cardiac depolarization and represents atrial depolarization; it is smooth and rounded, and one P wave must occur before each QRS complex.

PR segment

Indicates depolarization traversing the AV node.

T wave

Represents ventricular repolarization.

ST segment

Reflects the time interval between ventricular depolarization and ventricular repolarization (or between ventricular contraction and the beginning of ventricular recovery).

QT interval

Represents the time between the beginning of ventricular depolarization and ventricular repolarization.

PR internal

Indicates depolarization traversing the AV node.

QRS complex

Represents ventricular depolarization.

ECG Leads

• Lead I records tracings between the right arm and left arm.

• Lead II records tracings between the right arm and left leg.

• Lead III records tracings between the left arm and left leg.

12 Lead ECG

The standard ECG consists of 12 separate leads that record the electrical activity of the heart from 12 different angles. The ECG records a view of the heart on both a frontal and a transverse plane.