Tachyarrhythmias & Bradyarrhythmias

Hemodynamic Stability Screen ("The 4 Lethal Signs") & Pad Placement: Attach anterior-posterior (AP) defibrillator/pacer pads, continuous ECG monitor, pulse oximeter, and cycle BP. Screen immediately for 1. Hypotension/Shock (SBP < 90 mmHg or MAP < 65 mmHg), 2. Acute Altered Mental Status, 3. Ischemic Chest Pain, or 4. Acute Cardiogenic Pulmonary Edema [1,2].

Biphasic Defibrillator / Transcutaneous Pacer (AP pad placement preferred for AF/Atrial Flutter and Pacing); 2× Large-Bore IVs (18G antecubital)

AP pad placement sandwiches the left and right atria directly within the transthoracic current vector, lowering the defibrillation/cardioversion threshold and maximizing capture during transcutaneous pacing (TCP) [1,3].

Unstable Tachycardia (≥ 150 bpm with Lethal Signs) → Immediate Synchronized Cardioversion: Provide rapid procedural sedation/analgesia if conscious (Etomidate 0.1–0.15 mg/kg IV or Ketamine 0.5–1 mg/kg IV + Fentanyl 50 mcg IV). ENGAGE THE "SYNC" BUTTON (verify R-wave markers on every QRS). Deliver biphasic synchronized shock: SVT / Atrial Flutter: 50–100 J; Atrial Fibrillation: 120–200 J; Monomorphic VT: 100 J (Polymorphic VT / TdP: Unsynchronized Defibrillation 200 J) [1,4].

Biphasic Defibrillator in Synchronized Mode (Hold shock button down until R-wave discharge occurs)

Synchronizing shock delivery to the peak of the R-wave (absolute refractory period, Phase 1–2) prevents electrical discharge during the vulnerable peak/downslope of the T-wave (relative refractory period, Phase 3), which otherwise induces catastrophic R-on-T Ventricular Fibrillation [1].

Unstable Bradycardia (< 50 bpm with Lethal Signs) → Atropine, Epinephrine & Transcutaneous Pacing: Administer Atropine 1 mg IV push every 3–5 minutes (Max 3 mg) [1,5]. If no immediate response or high-grade infranodal block (Mobitz II or 3rd-Degree Wide-QRS), start Epinephrine infusion 2–10 mcg/min and initiate Transcutaneous Pacing (TCP) at Rate 70–80 bpm, increasing current (mA) from 30 mA upward until electrical and mechanical capture (femoral pulse / plethysmograph waveform) is confirmed, then set output 10 mA above threshold [1,5].

Dedicated IV line; Transcutaneous Pacer + Sedation/Analgesia (Ketamine 0.25–0.5 mg/kg IV or Fentanyl 25–50 mcg IV + Midazolam 1–2 mg IV)

Atropine competitively antagonizes postganglionic M₂ muscarinic receptors at the SA and AV nodes, reversing vagal acetylcholine-mediated IK₋ACh potassium efflux [1,5]. Because vagal fibers do not innervate the His-Purkinje system below the AV node, infranodal blocks require direct β₁-adrenergic agonism (Epinephrine) or external electrical depolarization (TCP) [1,5].

Stable Narrow-Complex Regular Tachycardia (SVT) Execution: Perform the REVERT Modified Valsalva Maneuver (40 mmHg strain for 15 sec sitting → immediate supine + 45° passive leg raise for 15 sec) [2,6]. If refractory, administer Adenosine 6 mg rapid IV push via a large proximal vein using a two-syringe/3-way stopcock technique followed immediately by a 20 mL 0.9% NaCl flush; if no conversion in 1–2 min, give Adenosine 12 mg rapid IV push (reduce initial dose to 3 mg if central line, heart transplant, or on dipyridamole/carbamazepine) [1,2].

10 mL syringe (blown to 40 mmHg) or manometer; 3-way stopcock in antecubital IV with continuous 12-lead ECG strip recording

The REVERT leg-raise surges venous return to the right atrium during the relaxation phase (Phase IV of Valsalva), stretching carotid/aortic baroreceptors to amplify reflex vagal efferent firing (43% conversion vs. 17% standard Valsalva; NNT = 3) [6]. Adenosine activates A₁ purinergic receptors in the AV node, opening IK₋Ado channels to hyperpolarize the membrane and transiently extinguish AV nodal conduction (t₁/₂ < 10 sec) [1,2].

Stable Wide-Complex Tachycardia (WCT) & Torsades de Pointes (TdP) Execution: Assume all undifferentiated regular WCT (QRS ≥ 120 ms) is Ventricular Tachycardia (VT) until proven otherwise. First-line pharmacotherapy for stable monomorphic VT without severe HFrEF: Procainamide 20–50 mg/min IV (or 10 mg/kg over 20 min) up to 17 mg/kg (PROCAMIO trial) [4,7], OR Amiodarone 150 mg IV over 10 min [1,4]. If Polymorphic VT with Prolonged QT (TdP): give Magnesium Sulfate 2 g IV over 5–15 min, Potassium Chloride to target K⁺ > 4.5 mEq/L, and initiate Isoproterenol 2–10 mcg/min or Overdrive Pacing at 100–120 bpm [1,4]. If Pre-Excited AF (WPW): give Procainamide or Ibutilide 1 mg IV over 10 min (or Synchronized Cardioversion) [2,3].

Smart Infusion Pump; Continuous QRS and QT interval monitoring

Procainamide (Class Ia) blocks open fast inward Na⁺ channels (INa) in His-Purkinje and accessory pathway tissue, terminating VT twice as effectively as Amiodarone with one-fourth the major adverse cardiac events [7]. In TdP, MgSO₄ suppresses Early Afterdepolarizations (EADs) by blocking L-type calcium channels (ICa₋L), while overdrive pacing shortens the RR interval and reduces transmural dispersion of repolarization [4].