Midterms Lec (Part 1)

P wave

represents the electrical impulse starting in the SA node and spreading into the atria; represents atrial depolarization.

2.5 mm or less

normal height of P wave.

0.11 seconds or less (< 0.12 seconds)

normal duration of P wave.

QRS Complex

represents ventricular muscle depolarization.

< 0.12 seconds

normal duration of QRS complex.

T Wave

at the end of the last phase of ventricular repolarization.

U Wave

represent repolarization of the Purkinje fibers.

PR Interval

represents the time needed for SA node stimulation, atrial depolarization, and conduction through the AV node before repolarization.

3-5 small squares or 120-200 milliseconds

average interval for PR interval.

ST Segment

represents ventricular repolarization.

< 2-3 small squares (80-12 oms)

average duration of ST segment.

Osborn Wave

or J Point, where elevation or depression of ST segment is measured.

QT Interval

represents the total time for ventricular depolarization and repolarization.

0.32-0.40 seconds

normal duration of QT interval if heart rate is 65-95 bpm.

TP Interval

measured at the end of the T to the beginning of the next P.

Isoelectric Line

when no electrical activity is detected, the line on the graph remains flat.

PP Interval

used to determine atrial rhythm and atrial rate.

RR Interval

measure the ventricular rate and rhythm.

Sinus Bradycardia

low heart rate, regular rhythm; slow but steady.

Sinus Tachycardia

fast heart rate with irregular rhythm that varies with respiration.

Sinus Arrhythmia

when the SA node creates an impulse at an irregular rhythm; usually increases with inspiration and decreases with expiration.

Atrial Flutter

“saw-tooth” pattern; at least 250-350 bpm.

Atrial Fibrillation

no distinct P waves, irregularly irregular rhythm.

Ventricular Tachycardia

HR 150-250 bpm; P waves are often hidden in preceding T waves.

Supraventricular Tachycardia

3+ PVCs in a row; looks like a regular wide train-track pattern.

Ventricular Fibrillation

rapid but disorganized ventricular rhythm that causes ineffective quivering of the ventricles.

First-Degree AV Block

all the atrial impulses are conducted through the AV node into the ventricles at a slower rate than normal.

Second-Degree AV Block, Mobitz Type 1 (Wenckebach Phenomenon)

occurs when all but one of the atrial impulses are conducted through the AV nodes.

Second-Degree AV Block, Type 2 (Hay Block)

occurs when only some of the atrial impulses are conducted through the AV node into the ventricles.

Third-Degree AV Block (Complete Block)

occurs when no atrial impulse is conducted through the AV node into the ventricles.