Door-to-balloon time measures how quickly the healthcare system can deliver definitive reperfusion after care has begun within the patient’s care pathway. It is defined as the interval from first medical contact to balloon inflation during PCI. This focuses on system performance—from the moment EMS or hospital staff first engages with the patient to the moment the blocked artery is opened. This is why the other options don’t fit. From hospital arrival to balloon inflation misses prehospital contact and transport steps that occur before arrival. From symptom onset to balloon inflation includes patient delay in seeking care, which isn’t the aim of this metric. From ECG interpretation to balloon inflation ignores the many steps that happen after initial interpretation, such as activation of the cath lab and prep time.

Elevated potassium levels change the heart’s electrical stability and make dangerous rhythms much more likely. Potassium sits outside heart cells to help set the resting membrane potential; when it’s too high, the resting potential becomes less negative, sodium channels don’t recover promptly, conduction slows, and the ECG can show peaked T waves, widening QRS, and eventually dangerous rhythms like ventricular fibrillation. The priority is to stabilize the heart while reducing the potassium load. Calcium is given first to stabilize the myocardial membranes, buying time for other measures. Then insulin with glucose is used to move potassium back into cells, lowering the serum level quickly. If acidosis is present, bicarbonate helps by promoting cellular potassium shift and correcting the pH. Additional therapies such as beta-agonists, diuretics, or dialysis may be used depending on the situation and renal function. This approach aligns with treating hyperkalemia and its correction with calcium, insulin plus glucose, and bicarbonate. While hypocalcemia would require calcium, and hypernatremia or fluid restriction do not address the dangerous potassium surplus, and hypokalemia would require potassium replacement, these do not fit the scenario of an arrhythmia-predisposing hyperkalemia.

Targeted temperature management aims to protect the brain after a cardiac arrest by cooling the body to a controlled temperature, which lowers cerebral metabolic demand and reduces reperfusion injury, inflammation, and excitotoxic damage. This neuroprotective approach improves the chance of meaningful neurological recovery in patients who remain comatose after return of spontaneous circulation. It is indicated for eligible adults who are not awake or able to follow commands after ROSC, provided there are no contraindications. In practice this means applying controlled cooling to a target range (commonly 32-36°C) for a period such as 24 hours, with careful monitoring and support (including sedation and shivering control, electrolyte management, and gradual rewarming) to optimize neurologic outcome. The other ideas—preventing fever alone, normalizing heart rate, or rapidly restoring pulse—do not capture the primary purpose or the clinical indication of targeted temperature management. Fever prevention is a beneficial effect, but the main goal is neuroprotection. It does not directly regulate heart rate, and it does not by itself reestablish circulation or rapidly restore a pulse.

The main idea is recognizing how the ST elevations differ in location and shape between a true transmural infarction and pericarditis. In a STEMI, the injury affects a specific coronary territory, so the ST elevations are focal to that region and you often see reciprocal ST depressions in leads opposite the involved area. In pericarditis, the inflammatory process involves the whole pericardium, leading to diffuse ST elevations across many leads, and these elevations tend to be concave upward with accompanying PR-segment depression (often with PR elevation in aVR). So, the best description is that STEMI shows focal ST elevations with reciprocal changes, while pericarditis shows diffuse, concave ST elevations with PR depression.