Beck's triad (cardiology)
Beck's triad is a collection of three medical signs associated with acute cardiac tamponade, an emergency condition wherein fluid accumulates around the heart and impairs its ability to pump blood. The signs are low arterial blood pressure, distended neck veins, and distant, muffled heart sounds.
The fall in arterial blood pressure results from pericardial fluid accumulation increasing pressure on the outside of the heart that limits the maximum size the ventricles can stretch to. This limits diastolic expansion (filling) which results in a lower EDV (End Diastolic Volume) which reduces stroke volume, a major determinant of systolic blood pressure. This is in accordance with the Frank-Starling law of the heart, which explains that as the ventricles fill with larger volumes of blood, they stretch further, and their contractile force increases, thus causing a related increase in systolic blood pressure.
The rising central venous pressure is evidenced by distended jugular veins while in a non-supine position. It is caused by reduced diastolic filling of the right ventricle, due to pressure from the adjacent expanding pericardial sac. This results in a backup of fluid into the veins draining into the heart, most notably, the jugular veins. In severe hypovolemia, the neck veins may not be distended.
The suppressed heart sounds occur due to the muffling effects of the fluid surrounding the heart.
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