The "5 5 5 rule" in the context of amyloidosis refers to a specific diagnostic sign observed in cardiac amyloidosis, indicating more advanced stages of the disease. This rule is primarily identified through Tissue Doppler Imaging (TDI) on an echocardiogram, a non-invasive imaging technique used to assess heart function.
Understanding the 5 5 5 Sign
The "5 5 5" sign is characterized by abnormally low tissue velocities in the heart muscle. Specifically, it means that three key tissue velocities measured via TDI are all less than 5 cm/s.
These three velocities are:
- s' (Systolic Tissue Velocity): Measures the speed at which the heart muscle contracts during systole (the heart's pumping phase).
- e' (Early Diastolic Tissue Velocity): Measures the speed at which the heart muscle relaxes and fills with blood during early diastole (the heart's filling phase).
- a' (Late (Atrial) Diastolic Tissue Velocity): Measures the speed of myocardial motion during late diastole, associated with atrial contraction.
In patients with advanced cardiac amyloidosis, the heart muscle becomes stiff and infiltrated by amyloid proteins, impairing its ability to contract and relax efficiently. This stiffness leads to a significant reduction in these tissue velocities.
Significance in Cardiac Amyloidosis
The presence of the "5 5 5" sign is a strong indicator of advanced cardiac amyloidosis. It signifies severe myocardial dysfunction and restrictive physiology, where the heart chambers struggle to fill properly due to the stiffened walls.
| Velocity Measurement | Description | Normal Range | 5 5 5 Rule Threshold |
|---|---|---|---|
| s' | Systolic velocity of the myocardial wall | Typically > 5 cm/s | < 5 cm/s |
| e' | Early diastolic velocity, reflecting myocardial relaxation | Typically > 5 cm/s | < 5 cm/s |
| a' | Late diastolic velocity, reflecting atrial contraction contribution | Typically > 5 cm/s | < 5 cm/s |
When all three of these velocities fall below the 5 cm/s cutoff, it points towards significant impairment of both systolic and diastolic function, characteristic of the restrictive cardiomyopathy seen in more severe cases of cardiac amyloidosis.
