ECG Basics and Interpretation Flashcards

Vocabulary flashcards covering ECG basics, vectors, physiology, waveforms, intervals, paper measurements, and heart rate calculation methods based on Chapter 2 lecture notes.

ECG (Electrocardiogram)

Records the electrical activity generated by the heart; it does not directly measure mechanical contraction or cardiac output.

Isoelectric line

The baseline representing no net electrical activity detected by the lead; serves as the reference point for identifying elevations and depressions of ECG segments.

Cardiac vector

The direction and strength (magnitude) of electrical activity traveling through the heart.

Vector direction

The path the electrical impulse travels through the myocardium.

Vector magnitude

The amount of electrical force produced during depolarization or repolarization.

Upward (positive) deflection

An ECG waveform produced when depolarization travels toward the positive electrode.

Downward (negative) deflection

An ECG waveform produced when depolarization travels away from the positive electrode.

Biphasic waveform

Produced when the electrical impulse travels approximately perpendicular to the recording lead.

Depolarization

The movement of cardiac cells from a resting electrical state to an active state that triggers contraction.

Repolarization

The return of cardiac cells to their resting electrical state after depolarization.

P wave

The ECG wave representing atrial depolarization.

QRS complex

The ECG complex representing ventricular depolarization.

T wave

The ECG wave representing ventricular repolarization.

Atrial repolarization

An electrical event not normally visible on an ECG because it occurs during ventricular depolarization and is hidden within the QRS complex.

ST segment

The period between ventricular depolarization and repolarization; it should normally lie on or very close to the isoelectric baseline.

PR interval

The time required for the impulse to travel from the atria through the AV node to the ventricles; normally ranges from $0.12–0.20$ seconds ($3–5$ small boxes).

QRS duration

Measures ventricular conduction; normally less than $0.12$ seconds (less than $3$ small boxes).

QT interval

Total time for ventricular depolarization and repolarization; a prolonged interval increases the risk of torsades de pointes and other ventricular arrhythmias.

Small ECG box (time)

Represents $0.04$ seconds.

Large ECG box (time)

Represents $0.20$ seconds and contains five small boxes.

Paper Speed and Calibration

Standard paper speed is $25\,\text{mm/second}$ and standard calibration mark is $10\,\text{mm} = 1\,\text{mV}$.

Vertical axis (ECG paper)

Measures voltage (amplitude); one small vertical box equals $0.1\,\text{mV}$ and one large vertical box equals $0.5\,\text{mV}$.

Horizontal axis (ECG paper)

Measures time.

300 Rule

Heart rate method for regular rhythms calculated by dividing $300$ by the number of large boxes between two consecutive R waves.

Six-second rhythm strip method

Preferred heart rate method for irregular rhythms; count the QRS complexes in a strip of $30$ large boxes and multiply by $10$.

Nursing Assessment Rule

Nurses should never interpret an ECG without assessing the patient, as electrical activity does not always indicate effective mechanical cardiac function or perfusion.