What is Beck’s Triad?
Beck’s triad is a collection of three medical signs that are associated with acute cardiac tamponade. Cardiac tamponade is a medical emergency where excessive fluid accumulates in the pericardial sac around the heart, which impairs its ability to pump blood.
The concept of Becks triad was developed by Claude Beck in 1935, a resident and later Professor of Cardiovascular Surgery at Case Western Reserve University, a private university in Cleveland, Ohio.
Understanding Cardiac Tamponade
Cardiac tamponade is an acute condition. When present, blood surrounds the heart and puts so much pressure on it that it is unable to effectively pump blood. If not treated, it will essentially squeeze the heart until it stops.
There exists a pericardial sac surrounding the heart that’s made up of two layers, which together make up the pericardium. The space between these two layers of the pericardium is normally filled with about 25 to 50 mL of fluid.
This fluid essentially acts as a lubricant and allows the heart to contract and expand in a smooth fashion by minimizing friction. When excess fluid, like blood, fills the pericardial space, the pericardium is unable to stretch or expand to accommodate the increase in fluid.
If that pressure from the fluid becomes greater than the pressure in the heart’s chambers, the heart will begin to compress and lose its ability to pump blood to the lungs and the rest of the body.
The signs of acute cardiac tamponade are low arterial blood pressure, distended neck veins, and muffled and distant heart sounds. Healthcare providers might also notice narrowed pulse pressure.
Beck’s Triad – Three Components
The presence of Becks triad relies on three components, which are only present in a minority of cases of acute cardiac tamponade. Again, these three components are:
- Hypotension with low arterial blood pressure or narrowed pulse pressure
- Jugular venous distention
- Muffled heart sounds
Beck’s Triad Physiology
The following is a more in-depth explanation of the three components of Becks triad listed above.
With Becks triad, the fall in arterial blood pressure results from pericardial fluid accumulation that increases pressure on the outside of the heart. This pressure limits the maximum size the ventricles can stretch to.
In turn, this limits diastolic expansion, or filling, which results in a lower end-diastolic volume, or EDV, 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 can be seen by distended jugular veins while the patient is in a non-supine position. It’s caused by the 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 which drain into the heart, most notably, the jugular veins.
It should be noted that in severe hypovolemia, the neck veins may not be distended.
And lastly, the suppressed heart sounds occur due to the muffling or insulating effect of the fluid in the pericardial sac. When sound travels through fluid, it sounds distant or suppressed because it’s traveling through a thicker median.
Some other symptoms of cardiac tamponade that can accompany Beck’s Triad include:
- Tachycardia or a rapid heart rate
- Cold and clammy extremities
- Anxiousness and restlessness