| Wave/Interval | Represents | Normal Duration |
|---|
| P wave | Atrial depolarization (atria contract) | 0.06–0.12 sec; upright in lead II |
| PR interval | Atrial depolarization + AV node conduction delay | 0.12–0.20 sec (3–5 small boxes) |
| QRS complex | Ventricular depolarization (ventricles contract) | ≤0.12 sec (3 small boxes); >0.12 = bundle branch block or aberrant conduction |
| ST segment | Ventricular repolarization beginning; isoelectric normally | Elevation = STEMI; depression = ischemia or NSTEMI |
| T wave | Ventricular repolarization | Upright in most leads; peaked T = hyperkalemia; flattened/inverted = ischemia |
| QT interval | Total ventricular depolarization + repolarization | QTc ≤440 ms (men), ≤460 ms (women); prolonged QT = torsades risk |
| Rhythm | Rate | Key Features | Common Cause/Action |
|---|
| Normal Sinus Rhythm (NSR) | 60–100 | Regular; P before each QRS; PR 0.12–0.20; QRS <0.12 | Normal; no intervention |
| Sinus Bradycardia | <60 | All intervals normal; just slow rate | Athletes (normal); beta-blockers; hypothyroidism; inferior MI; treat if symptomatic (dizziness, syncope, hypotension) with atropine 1 mg IV or pacing |
| Sinus Tachycardia | >100 (usually <150) | All intervals normal; just fast rate | Pain, fever, anxiety, hypovolemia, anemia, PE; TREAT THE CAUSE — not the rate |
| Sinus Arrhythmia | 60–100 | Irregular (varies with respiration); P before each QRS | Normal variant, especially in young; no treatment |
| Rhythm | Rate | Key Features | Treatment/Nursing |
|---|
| PAC (Premature Atrial Contraction) | Varies | Early P wave with different morphology; QRS usually normal; compensatory pause | Usually benign; caffeine, stress; notify if frequent (>6/min) or patient symptomatic |
| SVT (Supraventricular Tachycardia) | 150–250 | Regular, very fast; narrow QRS; P wave may be hidden in T wave; abrupt onset/offset | Vagal maneuvers first (Valsalva, carotid massage — not both carotids); adenosine 6 mg rapid IV push if unstable; cardioversion if hemodynamically unstable; monitor closely |
| Atrial Flutter | Atrial: 250–350; Ventricular: 75–150 depending on block | "Sawtooth" flutter waves (F waves); regular ventricular rate; 2:1, 3:1, or 4:1 conduction ratio | Rate control (diltiazem, beta-blockers); rhythm control (cardioversion, ablation); anticoagulation (stroke risk) |
| Atrial Fibrillation | Atrial: 350–600 chaotic; Ventricular: 60–180+ irregular | Irregularly IRREGULAR ventricular rhythm; no discernible P waves; fibrillatory baseline; #1 cause of cardioembolic stroke | Rate control (metoprolol, diltiazem, digoxin); rhythm control (amiodarone, cardioversion); ANTICOAGULATION (warfarin, DOACs) to prevent stroke; assess for hemodynamic instability |
| Type | PR Interval | QRS | Pattern | Treatment |
|---|
| 1st Degree AV Block | >0.20 sec (prolonged); CONSTANT | Normal | Every P conducts to QRS; just delayed | Usually benign; monitor; no treatment needed unless symptomatic |
| 2nd Degree Type I (Wenckebach/Mobitz I) | Progressive lengthening until one QRS drops | Normal | PR gets longer and longer, then one QRS missing; repeats cyclically | Usually benign; monitor; may need atropine if symptomatic; rarely progresses |
| 2nd Degree Type II (Mobitz II) | Constant PR interval | Wide (usually) | Occasional P without a following QRS (dropped beat) WITHOUT progressive PR lengthening | More serious; can progress to complete block; pacemaker often needed; NOTIFY PROVIDER |
| 3rd Degree (Complete Heart Block) | PR varies; no relationship between P and QRS | Wide (ventricular escape) or narrow (junctional escape) | P waves and QRS complexes march independently; atria and ventricles beat separately | EMERGENCY; temporary transcutaneous or transvenous pacing; permanent pacemaker |
| Rhythm | Rate | Key Features | Treatment |
|---|
| PVC (Premature Ventricular Contraction) | Varies | Wide, bizarre QRS (>0.12); no preceding P wave; full compensatory pause; T wave deflects opposite to QRS | Isolated: often benign; concerning if >6/min, multifocal, runs of 2+ (couplets/salvos), or R-on-T; treat underlying cause (hypokalemia, ischemia, hypoxia) |
| Ventricular Tachycardia (VT) | 100–250 | Wide QRS (>0.12); regular; 3+ consecutive PVCs; P waves absent or dissociated | Pulse present + stable: amiodarone, lidocaine; Pulse present + unstable: synchronized cardioversion; Pulseless VT: CPR + defibrillation (same as VF) |
| Ventricular Fibrillation (VF) | Chaotic; no organized rate | Chaotic, irregular, no P waves, no QRS, no T waves; completely disorganized electrical activity | IMMEDIATE CPR + UNSYNCHRONIZED defibrillation 200J biphasic; epinephrine + amiodarone every cycle; identify and treat reversible causes (H's and T's) |
| Torsades de Pointes | 150–250 | VT with QRS complexes that twist around the baseline; associated with prolonged QT; "turning of the points" | Magnesium sulfate 1–2g IV; correct QTc-prolonging medications; defibrillate if unstable/pulseless |
| Asystole | 0 — no cardiac activity | Flat line; confirm in two leads (rule out lead artifact) | CPR; epinephrine q3–5 min; identify reversible causes; poorest prognosis |
| Drug | Use | Key Nursing Points |
|---|
| Adenosine | SVT termination | 6 mg rapid IV push over 1–3 sec via large antecubital vein; flush with 20 mL NS immediately; patient feels brief chest pain/dyspnea; monitor for asystole (transient); have crash cart available |
| Amiodarone | V-Tach, V-Fib, A-Fib rate/rhythm control | 300 mg IV/IO push for pulseless VT/VF (150 mg for a second dose); 150 mg over 10 min for stable VT; monitor QT; pulmonary toxicity with chronic use; photosensitivity; thyroid dysfunction |
| Atropine | Symptomatic bradycardia, heart block (type I/II) | 1 mg IV q3–5 min; max 3 mg total; increases HR by blocking vagal tone; do NOT use in 3rd degree complete block (pacemaker needed) |
| Digoxin | A-Fib rate control, HF | Narrow therapeutic window; toxic at 2.0 ng/mL; signs of toxicity: nausea, yellow/green halos, bradycardia, heart blocks; treat toxicity with digibind (digoxin immune Fab) |
| Magnesium sulfate | Torsades de Pointes; eclampsia; hypomagnesemia | 1–2g IV slowly; monitor deep tendon reflexes (loss = first sign of toxicity); respiratory depression at high levels; calcium gluconate is antidote |
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