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Normal Sinus Rhythm

Key features: regular rhythm with normal intervals and waves. PR interval 0.12−0.20 s0.12-0.20\,\text{s}; QRS interval 0.04−0.12 s0.04-0.12\,\text{s}; heart rate 60−100 bpm60-100\,\text{bpm}; P to P and R to R intervals are equal; P waves upright and precede every QRS; all P waves and QRS complexes look the same.

Sinus Bradycardia

HR is slower (example around 48 bpm48\,\text{bpm}). PR and QRS are within normal ranges. If stable: monitor. If unstable: atropine 0.5 mg0.5\,\text{mg} IV push every 3−5 min3-5\,\text{min} up to a max of 3 mg3\,\text{mg}; consider external pacing (transcutaneous pacing) if needed.

Sinus Tachycardia

PR interval 0.12 s0.12\,\text{s}; QRS interval 0.08 s0.08\,\text{s}; HR about 136 bpm136\,\text{bpm}. If stable: no treatment. If unstable: treat the underlying cause (e.g., fever) to slow the rate.

Atrial Fibrillation (A fib)

Hallmarks: irregular rhythm and inconsistent P waves; lack of discrete P waves with a quivering atria. The ventricular rhythm is irregular due to variable AV conduction. For irregular rhythms, HR is found by measuring the narrowest R-R and the widest R-R to get a range of rates.

Atrial Flutter

Electrical impulse from an irritable atrial site creates flutter waves (sawtooth). Flutter waves occur at a fixed ratio to QRS (e.g., 4:1). PR interval cannot be measured. QRS is normal in duration if conduction is intact. Treatment mirrors A fib: rate control and consideration of rhythm control; cardioversion after anticoagulation if needed.

Premature Atrial Complexes (PACs)

Single early atrial beat with a normal QRS complex; followed by a compensatory pause as the heart resets. PACs are a single beat, not a rhythm. Common causes: hypoxia, stimulants, infection, toxicity. Management is usually monitoring; reduce triggers (e.g., caffeine) if they are frequent.

Premature Ventricular Complexes (PVCs)

Ventricular ectopic beats that occur early. No preceding P wave; wide and bizarre QRS (> 0.12 s0.12\,\text{s}); a compensatory pause follows. PVCs can be unifocal (all look the same) or multifocal (different shapes). Common patterns: couplets, bigeminy (PVC every other beat), trigeminy (every third beat). R-on-T phenomenon can precipitate VT. Frequency guides urgency; occasional PVCs are often benign, frequent PVCs may require intervention and treatment of underlying cause.

Ventricular Tachycardia (VT)

Ventricular rate > 150 bpm150\,\text{bpm}; P waves not seen; QRS is wide and (> 0.12 s0.12\,\text{s}). VT can be unsustained (< 30 sec30\,\text{sec}) or sustained (≥ 30 sec30\,\text{sec}). Categories: stable with a pulse, unstable with a pulse, pulseless.

  • If stable: monitor; consider amiodarone 150 mg150\,\text{mg} in saline over 10−15 min10-15\,\text{min}.

  • If unstable with a pulse: urgent cardioversion.

  • If VT without a pulse: treat as V-fib with CPR and defibrillation per ACLS.

Ventricular Fibrillation (V-fib)

Ventricles quiver without coordinated contraction. Coarse V-fib can be followed by fine V-fib; this is lethal due to no effective blood flow. Treatment: defibrillate; give epinephrine 1 mg1\,\text{mg} every 3−5 min3-5\,\text{min}; perform CPR.

Asystole

Complete absence of electrical and mechanical activity. Lethal rhythm. Treat with CPR and epinephrine; do not attempt defibrillation. Memory aid: "Asystole begins with A and ends with E, so always epi." (Epinephrine) + CPR.

You’ll practice rhythm strip interpretation weekly to reinforce these distinctions.