What is the evaluation approach for suspected hypoxia due to a right-to-left shunt (arteriovenous shunt)?

From the Guidelines

The evaluation approach for suspected hypoxia due to a right-to-left shunt (arteriovenous shunt) should begin with measurement of oxygen saturation in feet and both hands, as recommended by the 2018 AHA/ACC guideline for the management of adults with congenital heart disease 1. This approach is crucial in assessing for the presence of right-to-left shunting, particularly in patients with patent ductus arteriosus (PDA).

• The measurement of oxygen saturation in feet and both hands can help identify patients with right-to-left shunting, as cyanosis may manifest predominantly downstream from the ductal insertion into the aorta 1.
• Additional diagnostic tests, such as cardiac catheterization, can be useful in patients with PDA and suspected pulmonary hypertension, as it allows for the evaluation of pulmonary vasoreactivity, which carries prognostic significance 1.
• Invasive hemodynamic assessment, including pulmonary vascular resistance, is generally relied on for decision-making in patients with PDA and suspected right-to-left shunting 1.
• The use of contrast echocardiography with agitated saline, CT pulmonary angiography, and pulmonary function tests with diffusion capacity measurement can also be helpful in detecting intracardiac shunts, arteriovenous malformations, and other causes of shunt hypoxia 1.
• Shunt calculation can be performed using the shunt equation: Qs/Qt = (CcO2 - CaO2)/(CcO2 - CvO2), where Qs/Qt is the shunt fraction, CcO2 is end-capillary oxygen content, CaO2 is arterial oxygen content, and CvO2 is mixed venous oxygen content.
• Positional assessment may be helpful if platypnea-orthodeoxia syndrome is suspected, and common causes of shunt hypoxia include intracardiac defects, intrapulmonary shunts, and severe consolidation or atelectasis.
• It is essential to note that shunt hypoxia is refractory to supplemental oxygen because blood bypasses the alveoli entirely, preventing oxygen loading regardless of inspired concentration.
• The 2018 AHA/ACC guideline recommends that PDA closure in adults is recommended if left atrial or LV enlargement is present and attributable to PDA with net left-to-right shunt, PA systolic pressure less than 50% systemic and pulmonary vascular resistance less than one third systemic 1.
• However, the decision to close a PDA in adults with suspected right-to-left shunting should be made with caution, as morbidity and mortality are high when closure of a shunt is attempted in patients with Eisenmenger physiology with elevated pulmonary pressure and net right-to-left shunting 1.

From the Research

Evaluation Approach for Suspected Hypoxia due to a Right-to-Left Shunt

The evaluation approach for suspected hypoxia due to a right-to-left shunt (arteriovenous shunt) involves several steps, including:

• Clinical evaluation to determine the degree of right-to-left shunting 2
• Echocardiography with color Doppler and agitated saline to assess the presence and severity of the shunt 2, 3, 4, 5
• Transesophageal echocardiography (TEE) or intracardiac echocardiography (ICE) guidance for device closure 2
• Cardiac catheterization to rule out pulmonary hypertension 3, 5
• Surgical or percutaneous closure of the atrial septal defect to normalize oxygenation 2, 3, 4, 6, 5

Diagnostic Criteria

Diagnostic criteria for suspected hypoxia due to a right-to-left shunt include:

• Severe hypoxia with normal right-sided pressures 5
• Presence of a patent foramen ovale or atrial septal defect with right-to-left shunting 2, 3, 4, 6, 5
• Intermittent or persistent hypoxia, including platypnea-orthodeoxia syndrome 2, 4, 5
• Cyanosis without pulmonary arterial hypertension 5

Treatment Options

Treatment options for suspected hypoxia due to a right-to-left shunt include:

• Percutaneous closure of the inter-atrial defect 2, 5
• Surgical closure of the atrial septal defect 3, 4, 6
• Device closure using Amplatzer or Cardioseal devices 2