ECG Recognition

Study guide

FREC 4 assesses ECG recognition in its own invigilated exam, and this topic is shaped like that exam: a strip, and the question "what is this?". Rhythm recognition is a pattern-matching skill and it responds to volume — the useful revision here is repetition, in short and frequent sessions rather than long ones.

Normal and sinus rhythms

The baseline everything else is measured against. Get this group automatic before moving on.

• Normal sinus rhythm is defined by a rate in the adult range, regularity, and a consistent P wave before every QRS — all three, not any one.
• Sinus bradycardia and sinus tachycardia differ from it in rate alone, which is exactly why they make good distractors for each other.
• If you cannot say why a strip is NOT normal sinus rhythm, you are guessing on the harder groups.

Atrial and supraventricular rhythms

Where the P wave stops behaving. Two rhythms, and the differences are visual.

• Atrial fibrillation is recognised by an irregularly irregular rhythm with no consistent P wave — both features, and the irregularity is the more reliable one.
• Supraventricular tachycardia is fast and regular with the P waves lost in the complex, and rate alone will not separate it from sinus tachycardia.
• Practise these two against sinus tachycardia specifically; that is the three-way confusion the questions are built on.

Ventricular rhythms and ectopy

Wide complexes, and where they come from.

• Ventricular tachycardia is broad, regular and fast; the width of the complex is the finding that matters.
• Premature ventricular contractions are recognised as early, broad beats interrupting an otherwise normal rhythm.
• Counting and describing ectopics is assessed as well as naming them.

Conduction abnormalities

The blocks. The most systematic group, and the one that rewards a method.

• First degree block is a consistently long PR interval with every beat conducted — the relationship is constant.
• The two second-degree patterns differ in whether the PR interval lengthens before a beat is dropped or the drop arrives without warning; that distinction is the whole question.
• Third degree block has P waves and QRS complexes marching independently, and bundle branch block widens the complex without the rate change of a ventricular rhythm.

Cardiac arrest and ACS patterns

The rhythms that change what you do, plus ST elevation on a 12-lead.

• Ventricular fibrillation, asystole and pulseless electrical activity are distinguished on the strip and grouped by whether they are shockable — and PEA is the one defined by the patient, not the trace.
• A flat line is not automatically asystole; the checks that come before that conclusion are examinable.
• ST elevation is recognised on a 12-lead rather than on a rhythm strip, which is why it sits in its own group here.

In the exam Build a method and apply it identically every time: rate, regularity, P waves, PR interval, QRS width. Almost every wrong answer in this topic comes from recognising a strip by feel and skipping a step. The exam gives you a fixed and fairly short time, so speed comes from the method being automatic, not from rushing it.