This infant is exhibiting signs of shock (lethargy, mottling, delayed capillary refill, hypotension), making this unstable supraventricular tachycardia (SVT). According to PALS guidelines, unstable SVT requires immediate synchronized cardioversion. The initial dose is 0.5-1 J/kg. Adenosine is the treatment for stable SVT. While a fluid bolus is also indicated, it should not delay the definitive treatment of cardioversion.

An undifferentiated regular wide-complex tachycardia must be treated as ventricular tachycardia until proven otherwise. Administering an AV nodal blocking agent, such as the calcium channel blocker Verapamil (or Diltiazem), can block the AV node and remove any supraventricular drive, leading to profound hypotension or ventricular fibrillation if the rhythm is VT. Amiodarone and Procainamide are appropriate antiarrhythmics for stable VT. Adenosine may be used diagnostically.

This patient has atrial fibrillation with conduction over an accessory pathway (WPW), resulting in an irregular, wide-complex tachycardia. Administering an AV nodal blocking agent such as Diltiazem (a calcium channel blocker), Adenosine, or a beta-blocker is extremely dangerous. It can block the normal AV pathway, forcing all impulses down the fast accessory pathway, which can lead to ventricular fibrillation. Procainamide or Amiodarone are safer drug choices, and cardioversion is indicated if the patient becomes unstable.

The patient presents with signs of a beta-blocker overdose, which is refractory to atropine. Glucagon is the specific antidote for beta-blocker toxicity. It increases intracellular cAMP through a non-adrenergic pathway, leading to increased heart rate and contractility. Calcium chloride is for calcium channel blocker overdose, and sodium bicarbonate is for tricyclic antidepressant overdose.

The patient is in unstable bradycardia due to a third-degree AV block. Atropine is unlikely to be effective in high-degree blocks as its mechanism is at the AV node, which is already completely blocked. Transcutaneous pacing is the most reliable and immediate intervention to increase the heart rate and improve perfusion in this scenario. Dopamine or epinephrine infusions are second-line treatments if pacing is unavailable or ineffective.

Adenosine has a very short half-life and causes a transient block at the AV node, which feels unpleasant to the patient. Common side effects include flushing, shortness of breath, chest pressure, or a sense of impending doom. Warning the patient about these expected, brief side effects is a crucial part of patient care, improving their cooperation and reducing anxiety.

This patient presents with stable, regular, monomorphic wide-complex tachycardia, which should be presumed to be ventricular tachycardia. The first-line treatment is an antiarrhythmic infusion. Amiodarone 150 mg over 10 minutes is a primary agent. Diltiazem and Metoprolol (AV nodal blockers) are contraindicated as they can cause hemodynamic collapse if the rhythm is VT. Adenosine can be considered for diagnosis but an antiarrhythmic is preferred for treatment.

When you encounter a pacemaker malfunction scenario, you need to quickly assess whether the device is sensing, capturing, or both. This patient presents with failure to capture - you can see pacemaker spikes on the monitor, but they're not consistently followed by QRS complexes, meaning the electrical impulse isn't strong enough to stimulate the myocardium.

The correct management is D) Apply transcutaneous pacer pads and initiate external pacing. Since the permanent pacemaker is failing to capture and the patient is symptomatic with hypotension and dizziness from his bradycardia (intrinsic rate of 35), he needs immediate electrical pacing. Transcutaneous pacing can provide the higher energy needed to achieve capture when the internal pacemaker cannot.

Here's why the other options are inappropriate: A) Placing a magnet over the pacemaker puts it in asynchronous mode but doesn't solve the fundamental problem - the pacemaker still can't capture the myocardium effectively. B) Atropine 1 mg IV won't help because atropine increases intrinsic heart rate by blocking vagal stimulation, but this patient's bradycardia is due to pacemaker failure, not vagal tone. The pacemaker will continue firing inappropriately regardless of any increase in intrinsic rate. C) A fluid bolus addresses hypotension but ignores the underlying cause - inadequate cardiac output from severe bradycardia due to pacemaker malfunction.

Key takeaway: In pacemaker failure with hemodynamic compromise, your priority is restoring effective pacing. Look for capture failure (spikes without QRS) and be ready to initiate transcutaneous pacing immediately rather than trying indirect approaches.

When you encounter an unstable patient with a narrow-complex tachycardia that hasn't responded to initial treatments, you must quickly escalate to electrical cardioversion. This scenario tests your understanding of the ACLS tachycardia algorithm and when to prioritize immediate rhythm conversion over additional medications.

The correct answer is D because this patient shows clear signs of hemodynamic instability: hypotension (85/50), diaphoresis, and anxiety with a heart rate of 160. When vagal maneuvers and adenosine fail in an unstable narrow-complex tachycardia, synchronized cardioversion is the next intervention. The energy dose of 50-100 J is appropriate for the initial attempt at cardioverting supraventricular tachycardia.

Option A is incorrect because a second dose of adenosine (12 mg) can be considered, but only in stable patients. This patient's instability demands immediate electrical intervention rather than another medication trial.

Option B is wrong because diltiazem is contraindicated in unstable patients. Calcium channel blockers can worsen hypotension and should only be used in stable narrow-complex tachycardias after adenosine fails.

Option C is incorrect because amiodarone is primarily used for wide-complex tachycardias or atrial fibrillation with rapid ventricular response. It's not the first-line choice for unstable narrow-complex tachycardia, and the infusion time delays definitive treatment.

Remember: In ACLS, hemodynamic instability always trumps medication trials. When you see hypotension, altered mental status, chest pain, or pulmonary edema with any tachycardia, think electricity first, especially after initial interventions fail.

Effective pacing requires both electrical capture (a QRS complex following each pacer spike) and mechanical capture (a corresponding palpable pulse). This patient has electrical capture visible on the monitor, but her persistent hypotension suggests the heart is not contracting effectively with each paced beat. The paramedic must confirm mechanical capture by palpating for a pulse (e.g., carotid or femoral) that corresponds with the paced rhythm.