How to diagnose phrenic nerve injury after mitral valve stenosis surgery?

From the Guidelines

Diagnosing phrenic nerve injury after mitral valve stenosis surgery requires a comprehensive approach, starting with clinical assessment and imaging studies, and may involve specialized tests like nerve conduction studies and electromyography (EMG) for definitive diagnosis. The diagnosis of phrenic nerve injury is crucial for the management and prognosis of patients after mitral valve stenosis surgery.

Clinical Assessment

Begin with a thorough physical examination looking for signs such as elevated hemidiaphragm, decreased breath sounds at the affected base, and paradoxical diaphragmatic movement during respiration 1.

Imaging Studies

Chest X-ray is the initial imaging study of choice, which typically shows an elevated hemidiaphragm on the affected side (usually the left side after mitral valve surgery) 1.

• Fluoroscopy during sniff testing can demonstrate paradoxical upward movement of the affected diaphragm during inspiration.
• Pulmonary function tests often reveal restrictive patterns with decreased vital capacity, especially in the supine position.
• Ultrasound evaluation of diaphragmatic movement provides real-time assessment of diaphragmatic excursion and can detect paralysis.

Specialized Tests

For definitive diagnosis, nerve conduction studies and electromyography (EMG) of the diaphragm can confirm phrenic nerve dysfunction by measuring prolonged latency and decreased amplitude of diaphragmatic muscle action potentials. Phrenic nerve injury occurs in approximately 10% of cardiac surgeries due to direct cold injury from ice slush used for myocardial protection, mechanical trauma during internal mammary artery harvesting, or stretch injury during sternal retraction 1. Most injuries are temporary and resolve within 6-12 months, but persistent symptoms may require diaphragmatic plication in severe cases.

Management and Prognosis

The management of phrenic nerve injury after mitral valve stenosis surgery involves a multidisciplinary approach, including respiratory therapy, physical therapy, and potential surgical intervention for persistent symptoms. The prognosis for patients with phrenic nerve injury is generally good, with most patients experiencing resolution of symptoms within 6-12 months. However, early diagnosis and intervention are crucial to prevent long-term complications and improve quality of life.

From the Research

Diagnosing Phrenic Nerve Injury after Mitral Valve Stenosis Surgery

To diagnose phrenic nerve injury after mitral valve stenosis surgery, several factors and methods should be considered:

• The incidence of phrenic nerve injury can vary depending on the surgical techniques used and the patient's underlying condition, particularly pulmonary function 2.
• Mechanisms of injury include cold-induced injury during myocardial protection strategies, mechanical injury during internal mammary artery harvesting, hypothermia, mechanical trauma, and possibly ischemia 2, 3.
• Clinical responses to diaphragmatic dysfunction secondary to phrenic nerve injury can range from asymptomatic radiographic abnormalities to severe pulmonary dysfunction requiring prolonged mechanical ventilation 2.
• Diagnosis and management strategies may include early tracheostomy and diaphragmatic plication, which appear to be effective options for patients compromised by phrenic injuries 2, 4.
• Inspiratory-expiratory radiography can be used to assess phrenic nerve palsy, but it has limitations, including a high number of false negatives, and should not be relied upon for routine screening 5.

Diagnostic Tools and Techniques

Some diagnostic tools and techniques that can be used to diagnose phrenic nerve injury include:

• Inspiratory-expiratory chest radiography, which has a sensitivity of 56% and specificity of 93% for identifying phrenic nerve injury 5.
• Intraoperative phrenic nerve stimulation, which can be used to assess phrenic nerve function 5.
• Chest ultrasonography to assess diaphragmatic excursion 6.
• Pulmonary function testing to evaluate lung function 6.
• Cardiopulmonary exercise testing to assess exercise performance 6.

Patient Outcomes and Management

Patient outcomes and management strategies may include:

• Prolonged mechanical ventilation, ICU stay, and hospital stay in patients with diaphragmatic impairment 4.
• Surgical diaphragmatic plication to flatten the diaphragm in its inspiratory position, which can be an effective means of treatment in cases of respiratory impairment 4.
• Early spontaneous recovery of the phrenic nerve is rare, and treatment strategies should be tailored to the individual patient's needs 4.