ACLS rhythm recognition is the foundation of cardiac arrest management. This page covers shockable vs non-shockable arrest rhythms, peri-arrest tachycardias and bradycardias, and the clinical decision points that connect ECG recognition to ACLS algorithm branches.
Shockable rhythms require immediate defibrillation. VF and pVT are the only rhythms treated with defibrillation in adult ACLS.
Non-shockable arrest rhythms are treated with CPR, epinephrine, and finding the reversible cause. Do NOT defibrillate asystole or PEA.
For ANY tachycardia with hemodynamic instability (hypotension, altered mentation, pulmonary edema, chest pain with ischemic changes): synchronized cardioversion first.
Atropine works for nodal bradycardia (AV node block, vagal). It is unreliable for infranodal block (Mobitz II, CHB) — prepare pacing regardless.
After confirming pulselessness and beginning CPR, the first rhythm check determines the path. If VF or pulseless VT is confirmed: shock (200J biphasic, or 360J monophasic for VF), then resume CPR immediately for 2 minutes, then recheck. If asystole or PEA: NO shock — give epinephrine 1mg IV/IO, continue CPR, and aggressively search for reversible causes (6 Hs: hypovolemia, hypoxia, hydrogen ion/acidosis, hypo/hyperkalemia, hypothermia; 5 Ts: tension pneumothorax, tamponade, toxins, thrombosis-PE, thrombosis-coronary).
Synchronized cardioversion delivers an electrical shock timed to the QRS complex peak (R wave), preventing the shock from landing on the T wave and inducing VF (R-on-T). It is used for tachycardias WITH a pulse that are hemodynamically unstable: unstable SVT, AFib, atrial flutter, and VT with a pulse. It is NOT used for pulseless VT or VF (which requires unsynchronized defibrillation). The defibrillator must be set to 'synchronized' mode — confirm the sync marker is aligning with QRS complexes before delivering the shock.
Both amiodarone and lidocaine are acceptable per current ACLS guidelines for shock-refractory VF/pVT. Amiodarone (300mg IV bolus) is generally preferred as first-line because it has broader ionic channel effects and showed modest benefit in VF outcomes versus placebo in major trials. Lidocaine (1.5 mg/kg IV) is an acceptable alternative, particularly when amiodarone is unavailable or when the patient has known structural heart disease where lidocaine may be preferred. Neither drug reliably converts VF — defibrillation remains the definitive treatment.
NurseNest ECG training builds the interpretive foundation that ACLS builds upon. ACLS tells you what to do once a rhythm is identified — NurseNest training develops the skill to identify the rhythm correctly and confidently. The Core ECG module covers rhythm recognition from first principles. The Advanced ECG module includes ACLS-relevant scenarios: VT vs SVT with aberrancy, pulseless vs. pulsed rhythm management, defibrillation indications, and cardioversion decision-making. Both are integrated into your adaptive study loop for targeted weak-area practice.
PEA (pulseless electrical activity) is the most commonly misunderstood ACLS rhythm. It presents as an organized ECG rhythm — which novices confuse with a perfusing rhythm. The defining feature of PEA is the ABSENCE of a pulse despite organized electrical activity. The correct response is CPR + epinephrine + reversible cause search — NOT cardioversion, NOT rate control. The second most missed concept: that asystole must be confirmed in two ECG leads before withholding defibrillation, because fine VF (which IS shockable) can appear flat in a single lead.
Strip-based ACLS rhythm questions with mechanism-based rationales. Included with eligible RN and NP subscriptions.
