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The standard ECG paper speed is 25 mm/sec. This allows accurate measurement of intervals and waveforms. At this speed, one small box = 0.04 sec and one large box = 0.20 sec. A speed of 50 mm/sec may be used in pediatric or tachyarrhythmia cases for more detail, but the standard remains 25 mm/sec. Correct recognition ensures accurate interpretation and prevents misdiagnosis of conduction intervals.

Atrial flutter is caused by reentrant atrial activity at about 250–350 bpm. Flutter waves form a classic sawtooth pattern, most visible in inferior leads. Ventricular response depends on AV conduction (e.g., 2:1 conduction at 150 bpm). AF produces irregular fibrillatory waves with no distinct P waves. MAT shows multiple P wave morphologies. Junctional tachycardia originates from the AV junction and typically shows narrow QRS without sawtooth waves. Recognizing flutter is essential for guiding anticoagulation and rhythm control decisions.

V5 (and sometimes V6) shows the tallest R waves, reflecting left ventricular dominance. V1 and V2 normally have deep S waves, while aVL reflects the lateral wall but does not typically have the tallest R wave. R-wave progression is a key assessment in ECG interpretation.

Metal jewelry can introduce electrical interference, causing artifacts. It does not alter polarity directly, but artifacts can mimic arrhythmias. Removing jewelry ensures clean tracings. Impedance reduction and time efficiency are secondary considerations. Patient instruction improves test accuracy.

First-degree AV block is defined by a consistently prolonged PR interval (>0.20 sec) without dropped beats. In Mobitz I, PR gradually lengthens until a beat is dropped. Mobitz II shows constant PR with sudden dropped beats. Third-degree block demonstrates AV dissociation. First-degree AV block is often benign but should be documented, especially if associated with medications or conduction disease.