What is the most likely explanation for the sudden onset of dyspnea, lightheadedness, palpitations, and fatigue in a 78-year-old woman with a history of asymptomatic heart failure and hypertension, currently experiencing tachycardia, tachypnea, hypotension, and decreased oxygen saturation, with bilateral basilar crackles, an S3 heart sound, and lower extremity edema, with an ejection fraction of 35%?

Differential Diagnosis

• Single most likely diagnosis + B) Decreased left ventricular filling: The patient's symptoms of shortness of breath, light-headedness, palpitations, and fatigue, along with the physical examination findings of bilateral basilar crackles, S3 heart sound, and edema of the lower extremities, suggest acute decompensated heart failure. The decreased left ventricular filling can lead to a decrease in cardiac output, resulting in these symptoms. The patient's history of asymptomatic heart failure and reduced ejection fraction (35%) also supports this diagnosis.
• Other Likely diagnoses + D) Increased afterload: This could be a contributing factor to the patient's symptoms, as increased afterload can worsen heart failure. However, it is not the most likely primary explanation for the patient's presentation. + E) Increased venous tone: Although increased venous tone can contribute to heart failure symptoms, it is not a primary cause of acute decompensated heart failure.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.) + A) Cerebral thromboembolism: Although the patient's symptoms do not strongly suggest a cerebral thromboembolism, it is essential to consider this diagnosis, as it can be life-threatening and requires prompt treatment.
• Rare diagnoses + C) Diastolic dysfunction: While diastolic dysfunction can contribute to heart failure symptoms, it is less likely to be the primary cause of acute decompensated heart failure in this patient, given the presence of systolic dysfunction (ejection fraction of 35%).