The RV/LV ratio is a measurement used in medical imaging to assess the relative size of the heart’s two lower chambers, the right ventricle (RV) and the left ventricle (LV). Derived from diagnostic tests like CT scans or echocardiograms, this numerical comparison provides an objective indicator of potential strain on the heart. By comparing the diameters of these two ventricles, clinicians can quickly identify a structural abnormality that often signifies pressure overload, particularly on the right side of the heart. This ratio is a common tool for risk assessment, helping to guide immediate and long-term treatment decisions for various cardiovascular and pulmonary conditions.
Understanding the Right and Left Ventricles
The two ventricles of the heart have distinctly different roles that determine their normal size and structure. The right ventricle is responsible for pumping deoxygenated blood a short distance into the lungs through the pulmonary circulation. This is a low-pressure system, so the RV is naturally a thinner-walled and smaller chamber, often described as crescent-shaped.
The left ventricle, in contrast, must generate high pressure to pump oxygenated blood throughout the entire systemic circulation. To manage this high workload, the LV is significantly more muscular, has a thicker wall, and is the larger of the two chambers. This difference in size means that in a healthy heart, the diameter of the RV is expected to be substantially smaller than the diameter of the LV.
Measuring and Interpreting the Ratio
The RV/LV ratio is calculated by dividing the measured diameter of the right ventricle by the measured diameter of the left ventricle. This measurement is most commonly performed using Computed Tomography Pulmonary Angiography (CTPA) or echocardiography. When using CTPA, the diameters are typically measured in the axial plane at the widest point of both ventricles during the end-diastolic phase.
In a healthy individual, the ratio is less than 1.0, reflecting the LV’s larger size. An abnormal ratio occurs when the right ventricle enlarges due to pressure or volume overload, causing the numerical value to increase toward or beyond unity. A measurement of 0.9 or greater is a common threshold that signals right ventricular dilation, while a ratio of 1.0 or higher indicates that the RV is the same size as, or larger than, the LV.
Clinical Significance in Acute Conditions
The RV/LV ratio is most widely used in the acute setting to assess the severity of a pulmonary embolism (PE). A PE occurs when a blood clot lodges in the pulmonary arteries, creating a sudden, high-pressure obstruction that the right ventricle must overcome. An elevated ratio in this context directly indicates acute right ventricular strain, meaning the RV is struggling to pump blood against the blockage.
For a patient diagnosed with PE via CTPA, a RV/LV ratio greater than 1.0 is a predictor of adverse short-term outcomes, including hemodynamic collapse and increased risk of death. This finding helps classify the patient as having an intermediate-risk or “submassive” PE, which often dictates a more aggressive treatment plan. Clinicians use this objective measurement to determine if urgent interventions, beyond standard blood thinners, are necessary to support the failing right ventricle. The ratio is a tool for risk stratification, guiding immediate medical intervention.
Implications for Chronic Heart Health
Beyond acute events, the RV/LV ratio is relevant in chronic conditions that cause sustained pressure on the right side of the heart. Conditions such as pulmonary hypertension (PH) and advanced chronic heart failure (CHF) lead to long-term pressure overload in the pulmonary circulation. Over years, this sustained strain causes the right ventricle to undergo remodeling, a process where its walls thicken and the chamber progressively enlarges.
This chronic enlargement results in a persistently elevated RV/LV ratio, which is linked to a poorer long-term prognosis. In patients with PH, an elevated ratio is an independent predictor of mortality and disease progression. When the right ventricle fails to adapt to the chronic pressure, it can lead to right heart failure, which significantly worsens a patient’s functional capacity and overall survival, even when the left ventricle is functioning adequately.