Your 55-year-old male patient with hypertension and dyslipidemia is brought to the emergency department because of a 2-day history of heart palpitations, fatigue, and decreased exercise tolerance. He is easily winded while walking from the kitchen to his living room. He has no chest pain, dizziness, visual changes, edema, or orthopnea. Current medications include chlorthalidone and lovastatin. Currently, pulse is 100 beats/min, atrial rate is 310 beats/min, respiratory rate is 16/min, and blood pressure is 120/70 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 96%. Lungs are clear; heart rhythm is irregularly irregular and tachycardic. ECG shows negative F waves in leads II, III, and aVF, and positive F waves in lead V1. No edema is noted. Prominent vein pulsations of 305/min are noted. Which of these is the most likely diagnosis?

Your 70-year-old male patient with hypertension, MI, and coronary artery disease is brought to the emergency department because of a 1-hour history of shortness of breath and generalized weakness. He is clammy and is sweating profusely. Blood pressure is 90/58 mm Hg and ventricular rate is 157 beats/min. Lungs are clear; sustained tachycardia is noted. ECG shows a wide QRS of 162 msec with an LBBB pattern, beat-to-beat variation in the QRS morphology, delayed activation during initial phase of the QRS complex, and T-wave vector opposite the main QRS deflection. Which of these is the most likely diagnosis? 

Which of these is the most appropriate immediate next step for the previous patient?

Which of these is the most appropriate treatment for primary prevention of sudden cardiac death in the previous patient?

Your 75-year-old female patient is evaluated in the emergency department because of an acute ST-elevation myocardial infarction. She has a history of diabetes, end-stage renal failure, peripheral vascular disease, and coronary artery bypass graft surgery. Following placement of a cardiac stent, she is transferred to the ICU. The next day, evaluation shows a rapid, irregularly irregular ventricular rhythm with no discernible distinction between the QRS complex, the ST segment, and T waves. Physical examination reveals gasping respiration and purple discoloration of the skin. Blood pressure and pulse cannot be obtained, and heart sounds are absent. Which of these is the most appropriate next step?