Electrocardiogram (ECG) Interpretation

Comprehensive vocabulary flashcards covering the basic principles, components, intervals, and common abnormalities of adult electrocardiography (ECG) as presented in the lecture.

Electrocardiogram (ECG/EKG)

A graphical representation of electrical activity generated by the heart that serves as a noninvasive, inexpensive, and highly versatile diagnostic test.

Cardiac Depolarization

The initiating event for cardiac contraction, representing the stimulation phase recorded on an ECG.

Cardiac Repolarization

The recovery potentials generated by the heart, facilitating ventricular relaxation and filling.

Sinoatrial (SA) Node

Part of the conduction system that possesses spontaneous automaticity, starts the signal with the fastest depolarization, and provides normal control of the heart rate.

Atrioventricular (AV) Node

The part of the conduction system that slows conduction time and is responsible for the normal delay between atrial and ventricular conduction.

AV Junction

The region of the heart constituted by the atrioventricular (AV) nodal and His-bundle areas.

Purkinje Fibers

Specialized fibers that ramify to the ventricular myocytes to transmit depolarization wavefronts, triggering coordinated ventricular contraction.

P Wave

ECG component representing atrial depolarization; normally $< 120\text{ msec}$ in duration and best seen in lead II.

PR Interval

Measures the time between atrial and ventricular depolarization, normally between $120-200\text{ ms}$ ($0.12-0.20\text{ s}$), representing the physiological delay at the AV junction.

QRS Complex

ECG component denoting ventricular depolarization; normally between $100-110\text{ ms}$ or less ($2$ to $3$ small squares).

ST Segment

The phase of the ECG representing the plateau phase of repolarization following ventricular contraction.

T Wave

ECG component representing ventricular repolarization.

U Wave

A small rounded deflection ($\text{< 1 mm}$) following the T wave; abnormal increases in its amplitude are commonly due to hypokalemia or drugs like amiodarone and sotalol.

Standard ECG Calibration

Standard recording speed is $25\text{ mm/s}$, where $1\text{ mm}$ horizontally equals $40\text{ ms}$ and $1\text{ mV}$ vertically equals $10\text{ mm}$.

RR Interval

The interval between consecutive R waves used to compute the instantaneous heart rate.

300 Method

A method to calculate heart rate by dividing $300$ by the number of large ($0.20\text{ s}$) squares between R waves.

1500 Method

A method to calculate heart rate by dividing $1500$ by the number of small ($40\text{ ms}$) squares between R waves.

Rate-Corrected QT (QTc)

A calculated value representing the QT interval adjusted for heart rate; normal duration is generally $\text{< 440-450 ms}$.

Limb Leads

The six ECG leads (I, II, III, aVR, aVL, aVF) that record potentials transmitted onto the frontal plane.

Chest (Precordial) Leads

The six ECG leads (V1 through V6) that record potentials transmitted onto the horizontal plane.

Left Axis Deviation

A mean QRS axis that is more negative than $-30^{\text{°}}$.

Right Axis Deviation

A mean QRS axis that is more positive than $+90^{\text{°}}$ to $+100^{\text{°}}$.

P Mitrale

An ECG pattern of left atrial abnormality usually characterized by a notched P wave in lead II with an interpeak duration $> 40\text{ ms}$, classically seen in mitral stenosis.

P Pulmonale

An ECG pattern of right atrial abnormality characterized by a tall, peaked P wave in lead II ($> 2.5\text{ mm}$), often seen in pulmonary hypertension.

Sokolow-Lyon Voltage Criteria

Criteria for Left Ventricular Hypertrophy (LVH) defined as $SV1 + RV5 > 3.5\text{ mV}$ or $RaVL > 1.1\text{ mV}$.

Cornell Voltage Criteria

Criteria for Left Ventricular Hypertrophy (LVH) defined as $SV3 + RaVL > 2.8\text{ mV}$ for men or $> 2.0\text{ mV}$ for women.

Right Ventricular Hypertrophy (RVH) ECG Signs

Typically includes abnormally tall R waves in V1 ($> 0.6\text{ mV}$), right axis deviation, and deep S waves in leftward-directed leads.

Complete Bundle Branch Block

A condition where the QRS interval duration is $\text{ ≥ 120 ms}$; incomplete blocks range between $110$ and $120\text{ ms}$.

First-Degree Heart Block

A type of AV block where the conduction time is prolonged ($PR > 200\text{ ms}$) but all atrial impulses are conducted to the ventricles.

Mobitz Type I (Wenckebach) Heart Block

A second-degree AV block characterized by progressive lengthening of the PR interval until a QRS complex is dropped.

Mobitz Type II Heart Block

A second-degree AV block characterized by sudden, occasional, or repetitive blocks of conduction without prior PR interval lengthening.

Third-Degree (Complete) Block

An AV block where no atrial impulses are conducted to the ventricles, resulting in independent pacemakers for atria and ventricles.

Transmural Acute Ischemia

Ischemia involving the full thickness of the myocardium, typically manifested on ECG as ST segment elevation.

Subendocardial Ischemia

Ischemia characterized on the ECG by ST segment depression.

Electrical Alternans

A beat-to-beat alternation in the amplitude or configuration of ECG waves, characteristically seen in pericardial effusion.

Low Voltage QRS

Defined as a QRS amplitude $\text{< 5 mm}$ in all limb leads and $\text{< 10 mm}$ in all chest leads.