A dysrhythmia is any disturbance in the rate, rhythm, or conduction of the heart's electrical impulses. The normal impulse starts in the sinoatrial (SA) node (60–100/min), travels through the atria to the atrioventricular (AV) node, then down the bundle of His, bundle branches, and Purkinje fibers. Backup pacemakers are slower: AV junction about 40–60/min, ventricles about 20–40/min.

Why dysrhythmias matter: cardiac output = heart rate × stroke volume. Very fast rates shorten filling time; very slow rates reduce output directly; loss of atrial contraction (atrial fibrillation) removes the "atrial kick"; chaotic ventricular rhythms produce no output at all.

Mechanisms: altered automaticity (ischemia, catecholamines, stimulants), reentry circuits (SVT, atrial flutter, VT), and conduction block (AV blocks).

Common causes: myocardial ischemia or infarction, heart failure, valvular disease, electrolyte imbalance (especially potassium and magnesium), hypoxemia, acidosis, drug effects or toxicity (digoxin, QT-prolonging drugs), thyroid disease, stimulants (nicotine, cocaine, large amounts of caffeine), and sleep apnea.

Stimulants increase sympathetic activity and myocardial excitability (irritability), which can trigger premature beats and tachydysrhythmias.

Always assess the client, not the monitor. The same rhythm may be tolerated by one client and life-threatening in another.

Signs of instability (poor perfusion)

• Hypotension, acute altered mental status, signs of shock
• Ischemic chest discomfort
• Acute heart failure (dyspnea, crackles)
• Syncope or near-syncope

Other findings: palpitations, fatigue, dizziness, anxiety, irregular pulse, pulse deficit (apical rate higher than radial rate, typical of atrial fibrillation).

First action when a monitor shows a lethal-looking rhythm: check the client's responsiveness and pulse (the lead may simply be disconnected).

Normal ECG intervals (at standard paper speed, 1 small box = 0.04 s; 1 large box = 0.20 s)

Rate from a strip: count QRS complexes in 6 seconds × 10 (irregular rhythms), or 300 ÷ number of large boxes between R waves (regular rhythms).

Systematic analysis: rate → regularity → P waves → PR interval → QRS width → QT → identify rhythm → assess the client's response.

Electrolyte ECG clues: hyperkalemia → peaked T waves, then wide QRS; hypokalemia → ST depression, flat T, U waves, ventricular ectopy; hypocalcemia → long QT; hypomagnesemia → torsades risk.

Other tests: 12-lead ECG, continuous telemetry, ambulatory (Holter or patch) monitoring, event recorders, electrolytes (K⁺, Mg²⁺, Ca²⁺), thyroid function, drug levels (digoxin), echocardiogram, electrophysiology study.

Rhythm recognition

Adult ACLS priorities (current AHA guidance)

Cardiac arrest (no pulse)

• High-quality CPR: rate 100–120/min, depth at least 5 cm (2 in) but not more than 6 cm (2.4 in), full recoil, minimal interruptions, 30:2 until an advanced airway is placed (then 1 breath every 6 seconds with continuous compressions)
• VF / pulseless VT: defibrillate as soon as possible → resume CPR immediately for 2 minutes without a pulse check → rhythm check. Epinephrine 1 mg IV/IO every 3–5 minutes after initial defibrillation attempts fail. For refractory VF/pVT, amiodarone (300 mg, then 150 mg) or lidocaine (1–1.5 mg/kg, then 0.5–0.75 mg/kg) may be given
• Asystole / PEA: CPR and epinephrine as soon as feasible; no shock; search for reversible causes (the H's and T's: hypovolemia, hypoxia, hydrogen ion/acidosis, hypo-/hyperkalemia, hypothermia; tension pneumothorax, tamponade, toxins, thrombosis — pulmonary or coronary)
• Vascular access: peripheral IV first; intraosseous if IV is unsuccessful or not feasible

Bradycardia with poor perfusion

• Atropine 1 mg IV, repeat every 3–5 minutes to a maximum of 3 mg
• If ineffective: transcutaneous pacing, or dopamine or epinephrine infusion
• Mobitz II and complete heart block often do not respond to atropine — prepare for pacing; permanent pacemaker is definitive treatment for symptomatic complete block

Tachycardia with a pulse

• Unstable → synchronized cardioversion (sedate if possible). For AF, an initial biphasic energy of at least 200 J is preferred; 200 J is also reasonable for atrial flutter
• Stable, regular narrow-complex: vagal maneuvers → adenosine 6 mg rapid IV push with immediate saline flush, then 12 mg if needed
• Stable wide-complex: antiarrhythmic (e.g., amiodarone) and expert consultation

Cardioversion vs. defibrillation

Atrial fibrillation — three goals

1. Stroke prevention: stagnant blood in the atria forms clots → embolic stroke. Anticoagulate when annual stroke risk is about 2% or more (CHA₂DS₂-VASc ≥ 2 in men, ≥ 3 in women). Aspirin is not an alternative to anticoagulation for stroke prevention. Direct oral anticoagulants (apixaban, rivaroxaban, edoxaban, dabigatran) are preferred over warfarin, except with a mechanical heart valve or moderate–severe mitral stenosis (warfarin required)
2. Rate control: beta blocker (metoprolol) or nondihydropyridine calcium channel blocker (diltiazem, verapamil); digoxin as an add-on, especially with heart failure
3. Rhythm control: cardioversion, antiarrhythmics, catheter ablation. If AF has lasted 48 hours or more (or unknown), anticoagulate for at least 3 weeks or exclude atrial thrombus by transesophageal echocardiogram first, and continue anticoagulation at least 4 weeks afterward

Drug safety

Devices: permanent pacemaker (bradycardia, heart block), implantable cardioverter-defibrillator (ICD) for prevention of sudden death, catheter ablation for SVT, flutter, and AF.

Listed in priority order.

1. Pulseless client — call for help, start CPR, attach defibrillator; VF/pVT: prepare and deliver defibrillation immediately, then resume compressions for 2 minutes right after the shock
2. Asystole — start high-quality compressions immediately; do not defibrillate
3. Unstable client with a pulse — oxygen if hypoxemic, IV access, 12-lead ECG, prepare for atropine/pacing (brad) or synchronized cardioversion (tachy)
4. Frequent PVCs — assess oxygenation and serum potassium and magnesium first; report runs of three or more
5. Cardioversion care — verify anticoagulation status, consent, sedation, synchronization mode on; re-activate sync before each repeat shock (many defibrillators revert to unsynchronized mode); if VF develops, turn sync off and defibrillate; ensure everyone is clear; monitor airway and rhythm afterward
6. Anticoagulant safety — monitor INR/aPTT, hemoglobin, and bleeding signs; fall prevention
7. Pacemaker care — monitor for failure to capture or sense, site infection or hematoma, hiccups (diaphragm pacing); limit arm movement on the insertion side as ordered

• Take anticoagulants at the same time daily; do not skip or double doses; report bleeding, black stools, or severe headache
• Warfarin: keep vitamin K intake consistent — do not stop eating green vegetables; regular INR tests; check with the provider before new drugs, herbal products, or supplements
• Limit stimulants that trigger palpitations (large amounts of caffeine, energy drinks, nicotine, decongestants); avoid illicit drugs
• Report palpitations, dizziness, fainting, chest pain, or dyspnea
• Amiodarone: report new cough or breathlessness; use sun protection; keep laboratory appointments
• Pacemaker/ICD: carry the device card; keep cell phones about 15 cm (6 in) from the device; avoid strong magnets; MRI only if the device is labeled MRI-conditional and per protocol; if an ICD shocks more than once or the client feels unwell, call emergency services
• Teach family members CPR

• Assess the client first — pulse and responsiveness before treating the monitor
• VF = defibrillate; after any shock, resume CPR immediately for 2 minutes
• Asystole = CPR + epinephrine, never shock
• VT: pulse check decides — pulseless = defibrillate; unstable with pulse = synchronized cardioversion
• Epinephrine 1 mg every 3–5 minutes: ASAP in nonshockable rhythms; after initial shocks fail in shockable rhythms
• Symptomatic bradycardia: atropine 1 mg (max 3 mg) → pacing; complete heart block → permanent pacemaker
• SVT: vagal maneuvers → adenosine 6 mg rapid push + flush, then 12 mg
• AF: irregularly irregular, no P waves; anticoagulation prevents stroke; rate control with beta blocker or diltiazem
• Warfarin → INR 2.0–3.0 for AF/VTE (higher for some mechanical valves); consistent (not zero) vitamin K
• PVCs → check potassium and magnesium
• Torsades → magnesium sulfate
• Amiodarone → pulmonary fibrosis, thyroid and liver toxicity