Ekg

Lead II

An Electrocardiogram (ECG or EKG), derived from the German term Elektrokardiogramm, is a graphical representation generated by an electrocardiograph. This graph portrays the electrical voltage traversing the heart as a continuous strip. The primary instrument for cardiac electrophysiology, its predominant role is in the detection and diagnosis of cardiovascular diseases.

Applications of ECG

ECG holds extensive utilities, such as:

Recognizing if the heart functions typically or has anomalies like extra or skipped heartbeats (cardiac arrhythmia). Potential to signal coronary artery obstructions, especially during or post a heart attack. Utility in detecting disturbances in potassium, calcium, magnesium, and other electrolyte levels. Identification of conduction irregularities like heart blocks and bundle branch blocks. It can reflect a patient's physical state during stress evaluations. Provides insights into the heart's physical status, for instance, in cases of left ventricular hypertrophy.

Lead Arrangement on ECG

Lead I

The ECG's construction is based on the electrical potential measured at different body points. Leads I, II, and III span the limbs: Lead I goes from the right to the left arm, II from the right arm to the left leg, and III connects the left arm to the left leg. Using these, an imaginary central point V above the heart is conceived. The remaining nine leads are derived from potentials between this central point and the three limb leads (aVR, aVL, and aVF) along with the six precordial leads (V_1-6).

In total, there are twelve leads. Their inherent characteristics enable them to capture information from specific heart regions:

The inferior leads (II, III, and aVF) capture electrical activities from the heart's inferior region, representing the left ventricle's apex. The lateral leads (I, aVL, V₅, and V₆) record from the heart's lateral wall or the left ventricle's lateral wall. The anterior leads range from V₁ to V₆ and represent the left ventricle's frontal wall. aVR, albeit seldom used for diagnostics, validates the accurate placement of ECG leads on the patient. To gain valuable diagnostic insights, it's imperative to understand the regular and abnormal directions, or vectors, of both depolarization and repolarization. The right ventricle, having a lesser muscle mass, only makes a minor ECG imprint, making it harder to discern than left ventricle changes.

These leads capture the average electrical activity from the summation of heart action potentials at specific moments. For instance, during regular atrial systole, the summative electrical activity produces an electrical vector extending from the SA node to the AV node. This appears as the upright P wave in II, III, and aVF and as an inverted wave in aVR on the EKG.

Interpreting a Standard ECG

Annotated EKG diagram
P=P wave, PR=PR segment, QRS=QRS complex, QT=QT interval, ST=ST segment, T=T wave.

A standard ECG trace of a routine heartbeat encompasses a P wave, QRS complex, and T wave, with a minor U wave often going unnoticed.

Inclination Axis

The axis illustrates the electrical impulse's general trajectory through the heart. Typically directed bottom-left, it may veer right in taller individuals and left in those with obesity. Extreme deviations signal abnormalities like a bundle branch block, ventricular hypertrophy, or in rightward cases, a pulmonary embolism. The axis can also indicate rare conditions like dextrocardia, a direction reversal of the heart.

Wave Components

• P wave: Represents the current leading to atrial contraction. Both atria (atria) contract simultaneously. Its correlation with QRS complexes helps detect a heart block.
• QRS complex (T:10): Denotes the current causing the left and right ventricles' contraction, which is stronger than the atria's due to increased muscle mass, leading to a larger ECG deflection.
• T wave (T:13): Symbolizes the ventricles' repolarization. Since the QRS complex usually overshadows the atrial repolarization wave, it often remains unseen.

ECG Metrics

The QT interval spans from the QRS complex's inception to the T wave's end. Both the standard and the adjusted QT intervals are pivotal in diagnosing long QT syndrome and short QT syndrome. As the QT interval depends on the heart rate, several correction factors have been formulated to adjust the QT interval for the heart rate.

Historical Account

In the 19th century, the heart's electrical generation became evident. The first systematic approach from an electrical standpoint was taken by Augustus Waller at St Mary's Hospital in Paddington, London. In 1911, he still saw his work as having limited clinical relevance. The paradigm shift came with Willem Einthoven of Leiden, The Netherlands, who introduced the string galvanometer, more accurate than Waller's capillary galvanometer. Einthoven labeled the different deflections as P, Q, R, S, and T, detailing the electrocardiographic traits of several cardiovascular disorders. His groundbreaking work earned him the 1924 Nobel Prize for Physiology or Medicine.

Cultural Depictions

The ubiquity of ECG has made it a symbol for many medical bodies, juxtaposing it with traditional symbols like the Rod of Asclepius or caduceus. It embodies vitality and urgency. Popular television medical dramas often utilize an isoelectric ECG or flatline as a death metaphor or a sign of grave medical danger. In technical terms, this is called asystole, a type of cardiac arrest with a particularly adverse prognosis.

See Also

• Holter monitor
• Cardiac stress test
• Telemetry (medicine)
• Heart rate monitor
• Cardiac arrhythmia
• Cardiac cycle

References

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