From the Guidelines
Respiratory variation >50% on echo is not a specific indicator of any particular condition, but rather a sign that needs to be interpreted in the context of the patient's overall clinical presentation. When considering the provided evidence 1, it's essential to note that the guidelines discuss the diagnosis and management of pericardial diseases, including constrictive pericarditis. In constrictive pericarditis, Doppler echocardiography may show restricted filling of both ventricles with respiratory variation >25% over the AV-valves 1. However, a respiratory variation >50% is not specifically mentioned in the guidelines as a diagnostic criterion. Key points to consider in the diagnosis of constrictive pericarditis include:
- Clinical presentation with severe chronic systemic venous congestion and low cardiac output
- ECG findings such as low QRS voltage, generalized T-wave inversion/flattening, and atrial fibrillation
- Chest X-ray showing pericardial calcifications and pleural effusions
- M-mode/2D echocardiogram demonstrating pericardial thickening, RA and LA enlargement, and early pathological outward and inward movement of the interventricular septum
- Doppler findings of restricted filling of both ventricles with respiratory variation Given the lack of specific information on respiratory variation >50% in the provided guidelines 1, it's crucial to interpret this finding in the context of the patient's overall clinical presentation, considering factors such as volume status, cardiac function, and respiratory dynamics. In clinical practice, a respiratory variation >50% may be seen in various conditions, including hypovolemia, cardiac tamponade, and constrictive pericarditis, among others. Therefore, a comprehensive evaluation of the patient, including clinical history, physical examination, and additional diagnostic tests, is necessary to determine the underlying cause of the observed respiratory variation.
From the Research
Respiratory Variation on Echo
- Respiratory variation in transvalvular flow velocities can be used to diagnose cardiac tamponade, with a sensitivity of 77% and specificity of 80% for an inspiratory decrease > 22% in the peak velocity of the early mitral flow 2.
- A dilated inferior vena cava (IVC) is a marker of poor survival, and a dilated IVC that does not collapse with inspiration is associated with worse survival 3.
- The IVC diameter and its respiratory variation can be influenced by factors such as right atrial pressure, tricuspid regurgitation, body surface area, and age 4.
- A regression equation can be used to estimate mean right atrial pressure from the IVC maximum diameter and IVC collapsibility index, with a correlation coefficient of 0.43 4.
Factors Influencing Respiratory Variation
- Right atrial pressure is a major determinant of IVC diameter and respiratory variation, with higher pressures leading to increased IVC diameter and decreased collapsibility 4.
- Significant tricuspid regurgitation is associated with increased IVC diameter, independently of right atrial pressure 4.
- Body surface area and age are also independent determinants of IVC diameter, with larger body surface area and younger age associated with increased IVC diameter 4.
Clinical Implications
- Respiratory variation on echo can be a useful diagnostic tool for cardiac tamponade and other conditions affecting right atrial pressure 2, 3.
- IVC diameter and respiratory variation can provide valuable information on right atrial pressure and cardiac function, but should be interpreted in the context of other clinical and hemodynamic factors 4.