Abhilash Koratala, MD
Medical College of Wisconsin
In previous posts, we explored the identification of pericardial effusion through different cardiac windows using POCUS. Now that you know how to identify the effusion, let’s delve into the key findings that indicate tamponade physiology. Essentially, you want to know the hemodynamic significance of pericardial effusion. Just assessing the size of the effusion does not provide this information because the extent of heart compression is determined by the interplay between pericardial compliance and the rate of fluid accumulation. Even a relatively small pericardial effusion can cause tamponade if it accumulates rapidly and in chronic effusions, body has time for compensation and tamponade occurs when the volume exceeds the limit of pericardial compliance. We must pay attention to POCUS manifestations of the following processes to promptly recognize tamponade,
- Elevated central venous pressure (CVP): CVP increases in pericardial effusion as a compensatory mechanism to maintain the intracardiac pressure. Tamponade is almost always associated with elevated CVP and therefore, you can expect to see a plethoric IVC with minimal or no respiratory variation on POCUS. Exceptions apply, for instance, tamponade can occur even with a small, collapsible IVC in cases of severe volume depletion. Keep this in mind when evaluating onconephrology patients with effusions and concomitant hypovolemia.
- Right sided chamber collapse: Due to its lower pressures, the right heart is more susceptible to compression from a pericardial effusion, and abnormal filling of the right heart is one of the earliest indications of a hemodynamically significant pericardial effusion. On POCUS, look for right atrial collapse or inversion that starts in late ventricular diastole, when the intracavitary pressure is lowest and continues variably into the right ventricular ejection period; it generally exceeds one third of the cardiac cycle when significant. Also look for right ventricular collapse in early diastole (that’s when it’s supposed to fill and has lower pressure). Though the whole chamber can collapse in severe cases, more often it occurs at its weaker portion, that is right ventricular outflow tract (RVOT). It is less sensitive than atrial collapse but more specific for tamponade.
- Respiratory flow variation across cardiac valves: This is analogous to pulsus paradoxus. It happens because of the interdependence of the cardiac chambers in a space limited by pericardial effusion. During inspiration, more blood goes into the right heart pushing the interventricular septum to the left as ventricles share the septum and there is limited room for expansion of the free wall due to effusion. This increases flow velocities through the tricuspid valve and RVOT but reduces venous return to the left heart thereby decreasing the flow velocities through the mitral valve and left ventricular outflow tract (LVOT). During expiration, the opposite happens. By using pulsed wave Doppler, we can evaluate the respiratory flow variation across these valves (trans mitral flow is commonly used), providing insights into the presence of tamponade. Just to remind, anything that needs spectral Doppler is an advanced POCUS skill (need to pay attention to the angle of insonation and settings such as sweep speed/scale) and incorrect technique can lead to misleading or inaccurate conclusions.
- Hepatic vein Doppler: If you follow me on Twitter, you may already be acquainted with VExUS, a Doppler ultrasound method used to assess systemic venous congestion in fluid overload states. If not, please go through this article. In hepatic vein waveform, we commonly talk about systolic (S) wave reversal or decrease in amplitude when the right atrial pressure is high (meaning, venous return is impaired during systole but persists during diastole when the tricuspid valve is open). In tamponade, because the RV filling is impaired, the hepatic diastolic (D) wave diminishes or reverses, particularly in expiration (because of the septal bowing to the right).
- Left sided chamber collapse: This happens late in the course of tamponade and in nephrology practice, we are less likely to POCUS such sick patients with impending cardiac arrest.
Caution: It is important to note that the signs mentioned above may not be reliable or easily observed in patients who are mechanically ventilated or have elevated right-sided pressures at baseline (such as pulmonary hypertension) or localized effusions (e.g., post-cardiac surgery). Additionally, most patients with subacute tamponade are often hypertensive rather than hypotensive. Sudden reduction of preload in these patients (via ultrafiltration or excessive diuresis) can trigger tamponade physiology by lowering the intracardiac pressure relative to the pericardial pressure.
Now, let’s examine a real-life case and contextualize these findings in a clinical scenario. I was performing POCUS-enhanced physical examination on a patient who was recently started on hemodialysis. The blood pressure was approximately 165/100 mm Hg. Initially, the plan was to target 3-3.5 liters of ultrafiltration, assuming that hypertension in dialysis patients is almost always due to intravascular fluid overload. Interestingly, the patient did not have any pedal edema, and there was no apparent jugular venous distention. Of note, dialysis catheter was present in the right IJ vein. IVC was not well visualized due to numerous kidney and liver cysts (history of ADPKD). Then I performed hepatic vein Doppler expecting to see diminished or reversed S-wave suggestive of venous congestion. However, prominent D-reversals were noted in expiration. If you see D-reversal on hepatic vein waveform, think of 3 conditions – cardiac tamponade, constrictive pericarditis, and severe pulmonary hypertension. So, the next step is to look at the heart. Note that if you don’t have simultaneous EKG, it can be difficult to appreciate the phases of cardiac cycle.
Below are the parasternal long and short axes views of the heart demonstrating RVOT collapse during early diastole. Asterisk indicates pericardial effusion. M-mode through mitral valve leaflets and RVOT helps you better identify the collapse and its timing if your ultrasound machine doesn’t have EKG capability. Otherwise, we can easily confuse between systolic and diastolic collapse (during systole, RV anyways moves inward, we are looking for early diastolic collapse, when it’s supposed to fill). Go through this post for basics of M-mode. In the images below, note that the RV inversion coincides with E-wave (early diastolic) of the mitral valve.
Here we have apical 4-chamber view demonstrating atrial inversion. M-mode helps to identify its timing and duration.
Below are the pulsed wave Doppler images at the mitral valve, LVOT and RVOT. During inspiration, decrease in mitral E-wave (early diastolic) velocity by >25% and LVOT ejection wave velocity by >10% is considered significant. In the right heart, increase in tricuspid velocity by >35% and RVOT velocity by >10% with inspiration is significant. Sweep speed is set low here to accommodate more respiratory and cardiac cycles (i.e., you get more waves in the picture that are narrow). On the other hand, if you are measuring cardiac output by tracing these waves, sweep speed must be high (i.e., you’ll have less and broad-appearing waves in the frame).
Below is the subxiphoid cardiac view demonstrating pericardial effusion (asterisk). Atrial inversion can be noted. While this is a great view to demonstrate circumferential nature of the effusion and estimate its size, it can be a little tricky to evaluate chamber collapse due to variations in angle of insonation. I have seen inexperienced users mistakenly diagnosing tamponade based on this view. IVC was not well-visualized in this patient as mentioned and hence included an illustrative image from a different patient.
Verdict based on POCUS: Consult cardiology, reduce the goal ultrafiltration so that we don’t precipitate clinical tamponade during dialysis. Also, daily dialysis while in the hospital for presumed uremic pericardial effusion.
Below are images obtained using a handheld device after removing ~1.2 L fluid during dialysis. The RVOT collapse is qualitatively more prominent. What would have happened if we removed 3.5 L as originally planned?!
Reviewed by: Sam Kant
