Electrocardiogram Basics

Electrocardiogram (ECG)

• An ECG is a modified biphasic record of the heart's electrical activity during the cardiac cycle.
• The apparatus uses a sensitive galvanometer with a pen recorder that writes on a moving paper.
• An amplifier magnifies the potential changes recorded by electrodes attached to the galvanometer.
• Recording electrodes use a positive electrode connected to the positive pole of the galvanometer, and a negative electrode connected to the negative pole.
• Electrical currents of depolarization and repolarization within the heart travel through surrounding body tissues (thorax acts as a conducting medium).
• Electrodes placed on the body surface measure these currents.
• ECG waves represent depolarization and repolarization of atria and ventricles.

ECG Leads

• Leads measure the difference in electrical potential between two points, creating a complete circuit.
• These measurements come from two different points on the body (bipolar leads) or a certain point on the body (unipolar leads).

12 Standard Leads

• Three standard bipolar leads (lead I, lead II, lead III) are limb leads.
• Three augmented unipolar limb leads (aVR, aVL, aVF).
• Six unipolar chest leads (V1, V2, V3, V4, V5, V6) are also used.

Einthoven Triangle

• Einthoven, the scientist who first recorded ECGs, detailed lead placement based on this triangle.

Standard Limb Leads

• One positive and one negative electrode are employed on each limb.
• The positive and negative electrodes for each lead are detailed to show the view of the heart for each given lead.

Augmented Limb Leads

• One positive electrode is connected to a part, while the other two limbs act as a negative electrode.

Unipolar Leads

• The potential at one electrode (negative pole of the ECG) is set to zero.
• Another electrode (the positive exploring electrode) is placed on a limb or chest to record potential differences.

Chest Leads

• Potential differences are measured at points on the chest with a positive electrode and three other limbs as the negative electrode.
• The placements for each of the V leads (V1-V6) are detailed for their individual view of the heart.

Unipolar Chest Leads

• Detailed diagram depicting the placement of V1-V6 on a human torso.

ECG Paper

• The printed graph on paper for ECG measures amplitude (vertical) and time (horizontal).
• The details of this graph show how fast the ECG is recorded.
• 1 small square on the paper represents 0.04 seconds.
• A 1 large square represents 0.2 seconds.
• Amplitude is determined based on the paper's markings correlating to millivolts.

Waves of ECG

• Detailed representation and labelling of ECG waves, including P, Q, R, S, T, and U waves/segments.
• The P wave represents atrial depolarization; QRS complex represents ventricular depolarization; and T wave represents ventricular repolarization.
• QT interval, PR interval, and ST segment are also described.

Heart's Electrical Activity & ECG

• Detailed animation demonstrating the electrical activity of the heart and tracing of ECG waveforms corresponding to each step.

ECG Wave Components

• Detailed descriptions of the components of ECG waveforms, including corresponding lead labels, segments, intervals, and their significance.

Determination of Heart Rate from ECG

• Method for determining heart rate from the ECG by counting large boxes between R waves and using 300/number of large boxes or 1500 divided by the number of small boxes between R waves.

Detecting the Rhythm

• Criteria for recognizing a sinus rhythm, including presence of a positive P wave in leads I and II, and P wave preceding the QRS complex.

Normal Sinus Rhythm

• The characteristics of a normal sinus rhythm, emphasizing regular rhythm, normal rate, and a positive P wave followed by a QRS complex.