1 ECG Fundamentals and a Systematic Reading Method Free Online FlashCards

What is the difference between a lead and an electrode?

A lead is a view of electrical activity; an electrode is a body sensor. A standard 12-lead ECG uses 10 electrodes.

Which planes do limb and chest leads view?

Limb leads view electrical forces in the frontal plane; chest leads view them across the horizontal plane.

Where are V1 and V2 placed?

Place V1 in the fourth intercostal space at the right sternal border and V2 in the fourth intercostal space at the left sternal border.

Which ECG leads view the inferior region?

II, III, and aVF view the inferior region; I and aVL the high lateral region; V1–V2 the septal region; V3–V4 the anterior region; and V5–V6 the lateral region.

What are standard ECG speed and gain settings?

Standard settings are 25 mm/s and 10 mm/mV. At 25 mm/s, a small horizontal box is 0.04 s and a large box is 0.20 s; vertically, 10 mm equals 1 mV at 10 mm/mV.

What do the P wave and PR interval represent?

The P wave represents atrial depolarization. The PR interval runs from the beginning of the P wave to the beginning of the QRS and reflects atrial-to-ventricular conduction.

What does the QRS complex represent?

The QRS complex represents ventricular depolarization. A duration under 120 ms is generally considered narrow.

What are the ST segment and T wave?

The ST segment extends from the end of the QRS, at the J point, to the beginning of the T wave. The T wave represents ventricular repolarization.

What does the QT interval represent, and why assess QTc?

The QT interval runs from the beginning of the QRS to the end of the T wave and represents ventricular depolarization and repolarization. Because it varies with heart rate, assess QTc and verify automated values when needed.

How can ventricular rate be estimated on an ECG?

For a regular rhythm at 25 mm/s, estimate rate as $\frac{300}{\text{large boxes between consecutive R waves}}$. For an irregular rhythm, count QRS complexes in 10 seconds and multiply by 6.

What features help classify an ECG rhythm?

Check R–R regularity, whether P waves are present and similar, whether each P precedes a QRS, whether PR intervals are consistent, and whether QRS complexes are narrow or wide. Rate alone cannot identify a rhythm.

What axis does a positive QRS in both I and aVF usually suggest?

The common adult reference range is about $-30^\circ$ to $+90^\circ$. A QRS predominantly positive in both leads I and aVF usually indicates a normal axis.