The right ventricle-to-left ventricle ratio (RV/LV ratio) is a measurement used to assess the balance within the heart. This ratio compares the sizes of the heart’s two main pumping chambers, the right ventricle (RV) and the left ventricle (LV). A change in this ratio provides an immediate, non-invasive indicator of potential cardiac stress or dysfunction. It is frequently employed in urgent medical settings to quickly gauge whether the heart is experiencing acute strain. Understanding this measurement requires a look at the distinct work each side of the heart performs and the structural differences that result from their separate tasks.
What the Right and Left Ventricles Do
The heart functions as two separate pumps, with the right and left ventricles driving two distinct circulatory loops. The right ventricle (RV) is responsible for the pulmonary circuit, moving deoxygenated blood to the lungs to pick up oxygen. This is a low-pressure, short journey, as the blood only needs to travel a short distance through the pulmonary arteries.
The left ventricle (LV), in contrast, powers the systemic circuit, pushing oxygen-rich blood out to the entire body. This systemic loop requires great force to overcome the resistance of the body’s vast network of blood vessels. Consequently, the LV is structurally more robust, with a much thicker, more muscular wall than the RV.
Because the RV works against significantly less resistance than the LV, it is normally the smaller of the two chambers. This inherent structural difference is the foundation for interpreting the ventricular ratio.
Calculating and Visualizing the Ventricular Ratio
The RV/LV ratio is a quantitative measurement comparing the diameter of the right ventricle to the diameter of the left ventricle. This assessment is performed using medical imaging techniques, primarily echocardiography (Echo) or computed tomography (CT) scans. The measurement is typically taken across the widest point of both ventricles in the same imaging plane, often during diastole when the chambers are full.
Since the left ventricle is naturally larger and thicker, the normal ratio of the RV diameter to the LV diameter is less than 1.0. This means the RV is smaller than the LV, representing a healthy balance between the two pumps. The ratio offers a quick, objective snapshot of any recent changes in the size of the right heart chamber.
If the right ventricle begins to enlarge or dilate, the ratio will increase, signaling that the RV is struggling to pump blood effectively. A ratio approaching or exceeding 0.9 or 1.0 is generally accepted as the threshold for concern. A ratio at or above this value signals significant right ventricular dilation or strain.
The Ratio’s Critical Role in Diagnosing Acute Heart Strain
The most common application of the RV/LV ratio is in the risk stratification of patients with acute Pulmonary Embolism (PE). A PE occurs when a blood clot lodges in the pulmonary arteries, creating a sudden and severe blockage to blood flow from the right ventricle into the lungs. This obstruction causes an immediate spike in pressure within the pulmonary circuit, which the right ventricle must try to overcome.
The RV is not built to handle this high pressure, causing it to quickly dilate and become strained as it struggles to push blood past the blockage. When this dilation occurs, the RV/LV ratio increases, reflecting the acute heart strain. For a patient diagnosed with PE, a ratio significantly above 1.0 is a predictor of adverse outcomes, including a higher risk of short-term mortality.
This prognostic value makes the RV/LV ratio an important tool for clinicians. When a patient presents with PE, the measured ratio helps determine the urgency and aggressiveness of the required treatment. Other acute conditions that suddenly increase pressure on the RV, such as acute respiratory distress syndrome, can also cause the ratio to rise.