Electrocardiogram (EKG/ECG) Fundamentals and Machine Operation

Electrocardiogram (EKG/ECG)

A non-invasive diagnostic test that provides a graphic recording of the electrical conduction and activity of the heart over time; the equipment detects and records potential differences without producing or sending electric current to the heart.

Holter Monitor

An ambulatory monitor that continuously records the electrical activity of the heart during a patient's routine daily activities to capture transient electrical changes.

Dr. Augustus D. Waller

The physician (1856–1922) who demonstrated that electrical currents are generated during the human heartbeat, confirming discoveries first made in 1887.

Willem Einthoven

The inventor (1860–1927) of the first electrocardiograph and developer of the limb-lead equilateral triangle used in frontal plane EKG analysis.

Code Blue (Código Azul)

A hospital emergency designation used for urgent patient cases presenting with chest pain, acute rhythm changes, or cardiac arrest.

Sinoatrial (SA) Node

The natural pacemaker of the heart, located in the superior wall of the right atrium; it is elongated, oval, larger than the AV node, and generates impulses at an intrinsic rate of $60\text{--}100\,\text{bpm}$.

Internodal Tracts

Conduction pathways that spread impulses across both atria causing depolarization and contraction; includes the anterior internodal tract (Bachmann), medial internodal tract (Wenckebach), and posterior internodal tract (Thorel).

Atrioventricular (AV) Node

An oval conduction structure on the right side of the interatrial septum, approximately one-third to one-half the size of the SA node, that delays the electrical wave by approximately $0.10\,\text{s}$ before transmission to the bundle of His; possesses an intrinsic pacing rate of $40\text{--}60\,\text{bpm}$.

Bundle of His

A slender bundle of conducting fibers located on the right side of the interatrial septum just above the ventricles that connects the AV node to the bundle branches; has an intrinsic rate of $20\,\text{bpm}$.

Left Bundle Branch Divisions

Bifurcation of the left bundle branch consisting of the anterior fascicle (supplying the anterior and superior left ventricle) and posterior fascicle (supplying the posterior and inferior left ventricle).

Purkinje Fibers

A specialized network of conducting fibers distributed within the walls of both ventricles that triggers final ventricular depolarization and contraction; has an intrinsic rate of $10\,\text{bpm}$.

First Heart Sound ($S_1$ / "Lub")

The cardiac acoustic sound produced during ventricular systole by the closure of the atrioventricular (mitral and tricuspid) valves.

Second Heart Sound ($S_2$ / "Dub")

The cardiac acoustic sound produced at the end of ventricular systole by the closure of the semilunar (aortic and pulmonary) valves.

P Wave

The first positive deflection on an EKG tracing, produced by atrial depolarization and electrical activation.

QRS Complex

The waveform representing ventricular depolarization and atrial repolarization; composed of the initial negative deflection (Q wave), first positive deflection (R wave), and following negative deflection (S wave).

T Wave

The deflection appearing after the QRS complex that represents the ventricular repolarization recovery process.

U Wave

An occasional small wave appearing after the T wave, primarily visible in right precordial leads ($V_1$, $V_2$), generated by residual ventricular potentials and slow repolarization of the papillary muscles.

J Point

The exact anatomical junction where the QRS complex ends and the ST segment begins, marking the transition from ventricular depolarization to repolarization.

ST Segment

The normally isoelectric line running from the end of the QRS complex (J point) to the onset of the T wave, representing the early plateau/slow phase of ventricular repolarization.

PR Segment

The horizontal isoelectric segment located between the end of the P wave and the beginning of the QRS complex.

PR Interval

The time period measured from the beginning of the P wave to the onset of the Q wave or R wave, reflecting atrioventricular conduction time.

QT Interval

The duration measured from the start of the Q wave to the end of the T wave, representing total ventricular electrical systole (combined depolarization and repolarization).

Standard Paper Speed

The standard horizontal recording velocity of $25\,\text{mm/s}$, where one small grid square represents $0.04\,\text{s}$, one large square equals $0.20\,\text{s}$, and five large squares equal $1\,\text{s}$.

Standard Gain

The vertical calibration setting of $10\,\text{mm/mV}$, where an electrical signal of $1\,\text{mV}$ produces a $10\,\text{mm}$ ($2\,\text{large squares}$) deflection; calculated using $\text{Gain} = \frac{\text{height in mm}}{\text{voltage in mV}}$.

EKG Signal Chain

The sequential four-stage signal processing pathway: Skin and Electrodes $\rightarrow$ Patient Cable $\rightarrow$ Signal Processing $\rightarrow$ Display or Printout; a failure in any single stage distorts the tracing without any true change in cardiac activity.

Line Filter (Filtro de Línea)

An EKG machine setting designed to filter out and reduce alternating current ($\text{AC}$) electrical interference originating from the electrical power grid.

Muscle Filter (Filtro Muscular)

An EKG processing filter that reduces high-frequency baseline distortion and electrical noise caused by somatic muscle tension, shivering, or tremors.

Baseline Filter (Filtro de Línea Base)

An EKG signal filter that suppresses low-frequency, wandering shifts of the baseline caused by patient respiratory excursions or body movement.

Wandering Baseline

An EKG artifact characterized by slow, undulating shifts of the isoelectric line caused by patient respiration, body movement, or poor skin-electrode contact.

Somatic Tremor Artifact

An EKG artifact presenting as thick, erratic, and irregular baseline deflections caused by shivering, muscle tension, chills, or patient motion.

Alternating Current (AC) Interference

An EKG artifact presenting as uniform, rapid, consistent spikes along the baseline caused by nearby electrical equipment, power cords, or ungrounded wall sockets.

Einthoven's Law

The mathematical relationship governing frontal plane bipolar limb leads stating that the voltage of Lead II equals the sum of Lead I and Lead III ($\text{Lead II} = \text{Lead I} + \text{Lead III}$).

Bipolar Limb Leads

Frontal plane leads (I, II, and III) that directly compare electrical differences between a specific negative and positive limb electrode.

Augmented Unipolar Leads

Frontal plane limb leads (aVR, aVL, aVF) that use a single exploring positive electrode compared against an average reference voltage formed by the remaining electrodes.

Lead V1