Normal RV:LV Ratio

A normal RV:LV ratio is <1.0, with values ≥1.0 indicating right ventricular dilation and associated with significantly worse prognosis. 1

Standard Measurement Thresholds

An RV/LV ratio <1.0 is considered normal across multiple European Society of Cardiology guidelines for pulmonary embolism assessment 1
The 2019 ESC guidelines specifically illustrate that dilated RV with basal RV/LV ratio >1.0 represents pathologic right ventricular enlargement 1
Some studies have used RV/LV ratio >0.9 as the threshold for identifying RV dilation, which showed 64% prevalence in PE patients and strong prognostic value 1

The ratio should be measured in the four-chamber view from reformatted CT images or echocardiography, measuring the maximum diameter perpendicular to the long axis of each ventricle 1
On CT imaging, measure the distance between the ventricular endocardium and the interventricular septum, perpendicular to the heart's long axis 2
Measurements are typically obtained at the basal level (widest diameter) in end-diastole 1

RV/LV ratio >1.0 combined with vascular obstruction >40% increases 3-month PE-related mortality to 18.8% in the MAPPET registry 1
The negative predictive value of RV/LV >1.0 for uneventful outcome was 100% (95% CI, 94.3-100%), meaning a normal ratio essentially excludes high-risk PE 1
In intermediate-risk PE, patients with RV/LV ratio <1.03 and preserved RV function had only 1.0% 30-day mortality, while those with RV/LV ≥1.03 and impaired function had 46.2% mortality 3

For severe RV dilation using volume ratios, RV/LV volume ratio ≥2.30 defines severe dilation and is associated with significantly higher mortality in pulmonary hypertension 4
Moderate dilation corresponds to RV/LV volume ratio 1.70-2.29, and mild dilation to 1.27-1.69 4
These volume-based thresholds differ from diameter ratios but provide outcome-based severity grading 4

After simple instruction, RV/LV diameter ratio assessment is accurate and reproducible even by residents without CTPA experience, with kappa statistics of 0.83-0.94 compared to experienced radiologists 2
The average interobserver difference is minimal (SD 0.11-0.18), making this a practical bedside or radiologic assessment 2

RV/LV ratio >1.0 indicates RV dysfunction specifically in the context of acute PE, where it reflects acute pressure overload 1
In chronic conditions, the American Heart Association notes that RV adaptation to chronic pressure overload may maintain function despite dilation, requiring integration with other parameters like TAPSE and strain imaging 1
The ratio must be interpreted alongside clinical hemodynamics, biomarkers (BNP/NT-proBNP), and other echocardiographic findings such as septal flattening and tricuspid regurgitation 1

Do not rely on RV/LV ratio alone—10% of PE patients may have misleading findings such as significant LV dysfunction or valvular disease that affect interpretation 1
Severe tricuspid regurgitation can cause RV dilation independent of pressure overload, potentially overestimating dysfunction 1, 5
In mechanically ventilated patients, altered intrathoracic pressures limit reliability of RV assessment 5