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%). Normal cardiac output is approximately 3–6 L/min in an adult. Therefore, by removing a relatively small amount of fluid, a normal cardiac output may be restored.
A phased-array cardiac probe in the cardiac machine setting should be used. A curvilinear abdominal probe with 3.0–5.0 MHz frequency can also be used, particularly if the heart is imaged from the subxiphoid approach.
Tissue harmonic imaging (THI) should be used for all cardiac imaging if available. THI helps to brighten the signal returning from the pericardium and to improve the contrast between the anechoic blood-filled chambers and surrounding effusion. This will improve the image and make the procedure easier to perform.
Ideally, a pericardiocentesis kit or tray is used that includes proper equipment to introduce a catheter or pigtail using the Seldinger approach. This will allow a drainage catheter to be left in the pericardial sac in case there is reaccumulation of fluid and is also useful in patients transferring facilities. A stopcock with a sterile syringe and a drainage bag attached and taped in place is usually used in these patients. The syringe can be used to pull fluid off which can then be transferred to the bag by changing the position of the stopcock.
If these kits are not available, a spinal needle may be used to remove fluid acutely. It is important to keep in mind that the standard spinal needle is 3.5 in long or 8.9 cm in length (Fig. 20-1). While the pericardium may be as close as 2–3 cm when approached through a parasternal window, the distance may exceed the length of the needle from a subxiphoid approach (8–15 cm deep). Therefore, many of the “dry taps” resulting from this approach may be due to the needle being too short. Also, some of the “bloody taps” may be a result of hitting the liver as opposed to aspirating the right ventricle.
The two main approaches to the pericardium are subxiphoid and transthoracic. The traditional blind method uses a spinal needle attached to a large syringe inserted to the left of the xiphoid process, aiming toward the inferior tip of the left scapula. The success of this method is improved by elevating the head of the bed and dropping the heart down closer to the tip of the needle. This risks a decrease in the hydrostatic blood pressure supplied to the brain, and can be detrimental if performed on an already hypotensive patient.
More recently, the recommended approach used in the catheterization lab is a transthoracic one. This technique allows the pericardial space to be accessed by going through the least amount of tissue and obviates the need to elevate the head of the bed. The pericardium is usually 2–3 cm from the skin surface. The ultrasound transducer is placed on the chest wall and a safe place to insert the needle under direct observation is found. Usually, the needle insertion site will be located somewhere between the parasternal long-axis area and the apex. A spinal needle that is attached to a stopcock is then inserted into the pericardium. The stopcock is attached to a small syringe at a 90° angle to the needle (or tubing attached to a drainage bag), and also a 50-mL syringe that is in-line with the spinal needle. Back pressure is then applied to the larger syringe and the needle is advanced until fluid enters the syringe. In order to confirm that the needle is in the pericardial space, agitated saline can be placed in the smaller syringe and injected under ultrasound guidance. If the needle is in the correct place, the injected saline will appear as a “snowstorm,” such as seen in a child’s globe toy. Once confirmation is made, the saline can then be aspirated back out.
Ultrasound-guided pericardiocentesis can be either static or dynamic. In the static technique, the spot and the angle where the largest fluid collection may be accessed are noted and marked. The probe is then removed and the procedure performed. In dynamic guidance, the needle can be seen entering the pericardial space in real time. This has the advantage of ensuring the needle tip is in the pericardial space, but it may be technically difficult to place the probe and needle in the same spot. Therefore, this may require that the probe be placed in a different place than the needle (ie, subxiphoid view of a transthoracic pericardiocentesis), which can make visualization and orientation difficult.
In one of the largest series of ultrasound-guided pericardiocentesis, the Mayo Clinic recommends determining the largest collection of fluid accessible in a static technique and then performing the procedure. Using this technique, 85% of procedures were transthoracic. Other groups (particularly in Europe) have found good success with the subcostal approach. In either case, serial ultrasounds can confirm needle or catheter placement and assess the success of drainage.
This pitfall usually results from using the subxiphoid approach. The obvious solution to this problem is using a longer spinal needle or pigtail catheter that reaches the correct location. The transthoracic approach is useful in these situations as it places the needle closer to the pericardium. In addition, using the dynamic approach helps in order to confirm the needle is actually reaching the pericardial space in real time.
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