Cardiac procedures are typically performed by cardiology or cardiothoracic surgery physicians and though are less common in the emergency or critical care setting, may be life-saving when a patient is in extremis. Two situations where ultrasound guidance may be invaluable for cardiac procedures is in performing pericardiocentesis in a patient with tamponade and in guiding cardiac pacing in a patient with complete heart block or unstable bradycardia unresponsive to medications.
Pericardial effusion can present in very nonspecific ways, with isolated dyspnea, tachycardia, or hypotension. Patients with significant pericardial effusion and signs or symptoms of tamponade may require urgent pericardiocentesis. Ultrasound guidance is used to increase success and decrease complications of pericardiocentesis, and should be considered standard of care when feasible.
Pericardiocentesis is indicated for cardiac tamponade. It is usually performed prior to a pericardial window procedure, as it is quicker and less invasive. Most patients with tamponade can safely go to the cardiac catheterization lab for their procedure. However, there are times when the patient is too unstable and an emergency pericardiocentesis must be performed in the critical care setting. If there is no cardiologist available at the treating facility, then the emergency or critical care physician may need to perform the procedure in an unstable patient.
Tamponade occurs when cardiac filling is compromised due to extrinsic compression of the heart. Cardiac tamponade can occur with either small or large volumes of pericardial fluid. The quicker the fluid accumulates, the faster the rise in pericardial pressure compressing the heart. While true tamponade is a clinical diagnosis (hemodynamic compromise in the setting of pericardial effusion), signs of impending tamponade may be seen on a bedside echocardiography. The left side of the heart is used to higher pressures and has proportionally a larger and thicker muscular structure. Therefore, the thinner-walled right heart, with its lower pressures, will collapse first. Late diastolic collapse of the right atrium is seen first, followed by early diastolic collapse of the right ventricular free wall. A dilated inferior vena cava is typically present, indicating restricted filling. The physical findings of Beck's triad (hypotension, muffled heart sounds, and jugular venous distension) may be present with tamponade, however, they are not sensitive and do not provide much additional information when bedside ultrasound is available.
The first-line treatment of tamponade is to increase preload, typically with intravenous crystalloid. This effectively increases central venous pressure and right-sided heart pressures to compensate for the extrinsic pressure on the heart.
Pericardiocentesis removes extrinsic fluid volume from the pericardial sac, allowing the heart to fill. For example, if you withdraw 50 mL of fluid from the pericardial sac of a patient with tamponade, you have effectively allowed 50 mL more fluid into the heart for each beat. This will increase cardiac output by 3 L/min (50 cc × 100 × 0.6), assuming a heart rate of 100 beats per minute and an ejection fraction of 60%). ...