Real-time cardiovascular magnetic resonance subxiphoid pericardial access and pericardiocentesis using off-the-shelf devices in swine

Pericardiocentesis is a common catheter technique to sample or drain fluid from the pericardial space [1]. Pericardial access may be desirable even without effusion in certain procedures such as epicardial ablation of rhythm disorders [2], or atrial appendage exclusion [3]. Pericardiocentesis is performed using a long subxiphoid or transthoracic needle. Pericardiocentesis may be guided (A) using surface landmarks (“blindly”), (B) using electro-grams to detect epicardial needle contact, (C) using echocardiography, (D) using X-ray with- or without- contrast injections, or (E) using a combination. Each has advantages and limitations.

Typically, adjunctive imaging decreases procedural risk for difficult-to-access pericardial fluid collections (smaller volume, posterior location, loculated fluid, compartmentalized fluid collections, thick or calcified pericardium, large body habitus, etc.). In practice, most clinical techniques focus more on trajectory planning than on guiding live needle advancement to achieve pericardial access without bystander injury. Planar echocardiography imaging rarely allows the operator to view needle, neighboring vital structures, and target effusion simultaneously. Projection fluoroscopic imaging provides a large field of view, but uncertainty about three-dimensional position of soft tissue. Enhanced imaging guidance would be desirable.

We [4] and others [5‐9] use real-time cardiovascular magnetic resonance (CMR) to guide clinical heart catheterization by tissue and chamber visualization but without X-ray radiation. We hypothesize CMR can also guide pericardiocentesis. Real-time CMR depicts the entire thoracic context for needle access, allowing the operator to avoid critical structures including the liver, lung, pleural space, and heart muscle. We evaluate the safety and feasibility of real-time CMR guided needle pericardiocentesis in animals with and without pericardial effusions, using commercially available CMR-compatible (“passive”) access needles.

We found that real-time CMR guided pericardial access and pericardiocentesis was successful in every attempt. This included animals with small and no pericardial effusions. Procedures were quick with no complications. As expected, larger effusions were easier and faster to access. This was accomplished using off-the-shelf commercial CMR needles marketed in the US.

In this pre-clinical experience, we found real-time CMR guidance useful. CMR visualization of device, trajectory, and target enhanced operator subjective confidence in procedure steps. Objectively, pericardial access was achieved in all experiments without complications, irrespective of pericardial fluid volume, even in this early-stage experiment. The temporal resolution was adequate to guide the procedure in these animals with clinically-relevant tachycardia. Our success in animals having no effusion suggests potential value in other procedures requiring pericardial or epicardial access. The large field of view afforded by CMR may facilitate alternative, unconventional (mid-clavicular, mid-axillary) approaches to drain non-circumferential, difficult-to-access pericardial fluid [13], or very small pericardial effusions [14]. We only evaluated subxiphoid access because of the subxiphoid orientation of the porcine cardiac apex; in other work we accessed the porcine heart and pericardial space via intercostal approaches [15, 16].

In this experiment, we showed good success using “passive” commercial CMR needles that are visualized based on intrinsic materials properties. In other work, we have shown superior visibility using an investigational “active” antenna-needle (Figure 4) [17]. Both may enable more sophisticated non-surgical treatments for structural heart disease, including direct transthoracic implantation of large appliances into the heart [16].

Several limitations are noteworthy. Few clinical CMR systems currently are configured for interventional procedures including in-room display, interactive control, acoustic sound compression, open-microphone communications systems, and high-fidelity hemodynamic monitoring, although these represent a small incremental increase in cost. Even large-bore CMR systems constrain access to the chest or subxiphoid space, although we have found this readily surmountable even for sterile procedures in our preclinical experience and in human volunteers [data not shown]. Although we used clinical CMR needles, there are currently no commercially available safe and conspicuous CMR guidewires to be used in tandem with our access needle. Iron-doped polymer passive devices have shown mixed performance in early development [7]. We chose to use interleaved multiplanar CMR which creates a “saturation” artifact along their line of intersection that usually coincides with the desired needle trajectory (see Figure 2); this further limits the visibility of passive needles except when single-plane imaging is selected interactively. Passive needles are difficult to visualize outside the body before the operator commits to a needle trajectory. We believe active devices may enhance visibility and safety, and therefore we are developing clinical-grade active needles [17] and guidewires [18]. Finally, interventional CMR remains investigational and is not yet widely deployed.

In conclusion, we found real-time CMR allowed successful and rapid pericardial entry and pericardiocentesis in swine irrespective of pericardial volume, using off-the-shelf needle devices. Clinical testing is underway.