A 62 years old man with carcinoma of lung presented to emergency depament with respiratory distress. His EKG showed electrical alternans. The most likely diagnosis is
**Core Concept**
Electrical alternans is a rare but characteristic ECG finding associated with a specific type of cardiac tamponade, where the heart is compressed by fluid accumulation in the pericardial space, leading to an abnormal cardiac rhythm.
**Why the Correct Answer is Right**
Electrical alternans occurs due to the swinging motion of the heart within the pericardial space, causing alternating changes in the ECG waveform. This phenomenon is classically seen in cardiac tamponade, particularly in cases where the pericardial effusion is large and the heart is severely compressed. The swinging motion of the heart can lead to variations in the amplitude and direction of the P and QRS complexes, resulting in electrical alternans.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as electrical alternans is not a feature of cardiac failure, which typically presents with other ECG changes such as low voltage QRS, left ventricular hypertrophy, or ST segment depression.
**Option B:** This option is incorrect as electrical alternans is not a feature of pulmonary embolism, which typically presents with other ECG changes such as S1Q3T3 pattern, right bundle branch block, or T-wave inversion in the anterior leads.
**Option C:** This option is incorrect as electrical alternans is not a feature of myocardial infarction, which typically presents with other ECG changes such as ST segment elevation, Q waves, or T-wave inversion.
**Clinical Pearl / High-Yield Fact**
Electrical alternans is a critical ECG finding that requires immediate attention, as it may indicate cardiac tamponade, a life-threatening condition that requires prompt pericardiocentesis or surgical intervention.
**Correct Answer: C. Cardiac Tamponade**