Electrocardiograph Basics

The shape of the electrical signal during ventricular depolarization on an ECG.

Heart rate can be calculated from QRS complexes observed on an ECG, indicating the number of beats per minute.

There are five large squares on an ECG paper per second, influencing heart rate calculation.

Movement of the depolarization wave towards or away from the lead affects the QRS complex shape.

Occurs when the depolarization wave moves towards the lead, indicated by a larger R wave.

The PR interval is the time from the beginning of the P wave to the start of the QRS complex, reflecting conduction from SA node to ventricles.

The normal PR interval ranges from 120 to 220 ms, which corresponds to 3 to 5 small squares on the ECG.

Occurs when the depolarization wave moves away from the lead, indicated by a larger S wave.

The average direction of depolarization through the ventricles as seen from the front.

The QRS complex duration indicates how long it takes for excitation to spread through the ventricles and is normally 120 ms or less.

A normal QRS complex is 120 ms or less in duration; longer duration indicates conduction abnormalities.

Direction of depolarization spreading from 11 to 5 o'clock, predominantly positive in leads I, II, III.

In lead VR, depolarization usually shows downward (negative) deflection for normal axis.

A lead in ECG terminology refers to the electrical picture of the heart rather than just the wires connecting to the ECG recorder.

Electrodes placed on the body detect electrical signals from the heart for the ECG recorder, with specific placements for accurate readings.

Condition causing the cardiac axis to swing right due to hypertrophy of the right ventricle.

An electrocardiogram that records the heart's electrical activity.

Key segments include P wave, QRS complex, and T wave.

Represents atrial contraction in the ECG.

Indicates repolarization of the ventricles after contraction.

An extra wave after the T wave, uncertain origin, may indicate muscle repolarization.

ECG machines record at a standard speed of 25 mm/s.

Each large square on ECG paper equals 0.2 seconds.

Deflection becomes negative due to depolarization moving away from Lead I.

Deflection becomes positive as depolarization spreads towards Lead III.

Occurs when left ventricle hypertrophy affects QRS complex direction, making it predominantly negative in Lead III.

The QRS complex becomes predominantly negative in Lead II when the left ventricle is enlarged.

Cardiac axis is measured in degrees with Lead I at 0°, Lead II at +60°, and Lead III at +120°.

If S wave > R wave in Lead II, axis > 90° indicates right axis deviation.

Axis deviation alerts clinicians to search for ventricular hypertrophy signs despite minor significance in individuals' body types.

The QRS complex represents ventricular depolarization in ECG, shaped by interventricular septum and ventricular muscle mass.

The septum between the ventricles depolarizes before the walls, affecting the QRS shape.

The left ventricle has more muscle mass, dominating the ECG pattern compared to the right ventricle.

These leads monitor the right ventricle in the ECG, showing upward deflection first.

These leads look at the septum's activity during the QRS complex in ECG.

These leads assess the left ventricle, demonstrating upward deflection as muscle depolarizes.

The point where the R and S waves in the QRS complex are equal indicates the interventricular septum's position.

A condition where the SA node depolarizes normally, but there's a delay indicated by a prolonged PR interval.

A condition where excitation intermittently fails to pass through the AV node or bundle of His.

Complete heart block where atrial contraction occurs but no beats reach the ventricles; ventricles contract via escape mechanism.

Peaked P waves indicate right atrial hypertrophy; bifid P waves indicate left atrial hypertrophy, commonly from mitral stenosis.

Normal QRS duration is 120 ms or less, representing the conduction time through ventricles.

The ST segment lies between the QRS complex and the T wave, indicating the heart's recovery phase after depolarization.