|Year : 2014 | Volume
| Issue : 1 | Page : 18-23
Esophageal assessments of left ventricular filling pressures: A proof-of-concept study
Markus Meyer, Stephen P Bell, Neeraj Sardana, Richard Zubarik, Martin M LeWinter, Harold L Dauerman
Department of Medicine, Division of Cardiology and Gastroenterology, University of Vermont College of Medicine, Burlington, Vermont, USA
|Date of Web Publication||3-Mar-2014|
University of Vermont College of Medicine, Fletcher Allen Health Care, McClure 1, Cardiology, 111 Colchester Avenue, Burlington, Vermont 05401
Source of Support: This study is funded by general developmental funds (HL Dauerman) and by NIH R21 HL094807.01A1 to M. Meyer, Conflict of Interest: None
| Abstract|| |
Objective: We sought to evaluate if left ventricular filling pressures can be assessed from the esophagus.
Background: The invasive assessment of left ventricular filling pressures is of importance in the evaluation and monitoring of critically ill patients. The left atrium is in very close proximity to the esophagus. We hypothesized that the temporal pressure decay characteristics of an esophageal fluid volume positioned at the level ofthe left atrium should depend on the atrial and left ventricular filling pressure.
Materials and Methods: In five pigs an esophageal balloon was placed at the level ofthe left atrium. The balloon was then pressurized to 50 mmHg followed by an automated release that allowed us to directly record the pressure decay, while simultaneously recording left atrial pressures. An algorithm was developed to estimate atrial pressures. We also tested if invasive transesophageal atrial pressures can be recorded via an ultrasound guided left atrial puncture.
Results: Noninvasive transesophageal assessments of left atrial pressures are feasible. The left atrial pressure directly affects the esophageal pressure decay and correlates with the transition point from an exponential pressure decay to a more linear decay (r = 0.949). This approach also allows for the assessment of atrial waveforms. We could also demonstrate that invasive transesophageal pressure measurements are feasible and safe.
Conclusions: The esophagus allows for reproducible less invasive assessments of left ventricular filling pressures and atrial pressure waveforms. This close spatial relationship provides an alternative access site for diagnostic and therapeutic cardiac procedures.
Keywords: Diastolic filling pressures, esophagus, left atrium
|How to cite this article:|
Meyer M, Bell SP, Sardana N, Zubarik R, LeWinter MM, Dauerman HL. Esophageal assessments of left ventricular filling pressures: A proof-of-concept study. Int J Crit Illn Inj Sci 2014;4:18-23
|How to cite this URL:|
Meyer M, Bell SP, Sardana N, Zubarik R, LeWinter MM, Dauerman HL. Esophageal assessments of left ventricular filling pressures: A proof-of-concept study. Int J Crit Illn Inj Sci [serial online] 2014 [cited 2022 Dec 7];4:18-23. Available from: https://www.ijciis.org/text.asp?2014/4/1/18/128008
| Introduction|| |
The invasive assessment of left ventricular end-diastolic pressures is a key diagnostic parameter in the cardiovascular evaluation and monitoring of critically ill patients. This is typically achieved by right heart catheterization which has an inherent risk of complications. This creates a need for the development of less invasive methods to assess left ventricular filling pressures.
The esophagus is in very close proximity to the left atrium. When an endoscopic probe is passed through the esophagus, this spatial relationship is appreciated as atrial pulsations. In the assessment of the cardiovascular system, echocardiography is the only approach that takes advantage of this spatial relationship. To explore if left atrial pressures could be measured noninvasively in the esophagus, we developed a method that allowed us to record pressures. We hypothesized that the pressure decay of a pressurized fluid volume placed posterior to the left atrium is mainly determined by the left atrial pressure. Such measurements should be facilitated by the stable noncompliant support provided by the thoracic spine and luminal esophageal pressures that are equal to the ambient atmospheric pressure. Simultaneous conventional invasive measurements of left atrial pressures under varying conditions allowed us to investigate if this approach has clinical potential as an alternative method for assessing left ventricular filling pressures. We also sought to explore if invasive transesophageal pressure measurements are practical, and if the esophagus could serve as an access point for invasive cardiac procedures.
| Materials and Methods|| |
We performed left atrial and transesophageal left atrial pressure measurements in pigs. The use of these animals was approved by the Institutional Animal Care and Use Committee of the University of Vermont.
Animal surgery and instrumentation
Studies were performed in five farm-raised female pigs (mean weight 32.8 kg, range 28-37 kg). Meloxicam (0.2 mg/kg p.o.) was administered as a pre-operative analgesic followed by ketamine (20 mg/kg i.m.) and atropine (0.044 mg/kg i.m.). After endotracheal intubation, anesthesia was induced with isoflurane (5%) and maintained between 0.5 and 2%. The pigs were positioned in dorsal recumbency. Oxygen saturation, expired carbon dioxide levels, and limb lead electrocardiographic (ECG) recordings were monitored throughout the surgery. The sternum was opened through a midline incision. After positioning a rib spreader, the pericardium was opened and fixed with sutures to the chest wall to stabilize the heart. An adjustable ligature was positioned around the ascending aorta and a saline-filled catheter was introduced into the left atrial appendage to record pressures and waveforms. Left atrial pressure recordings were obtained at baseline, normal saline infusion (2000 mL) and after ascending aortic occlusion. Thereafter, ventricular fibrillation was induced by a direct electrical current. The heart was removed and the esophagus was dissected and visually inspected. The disposed carcass was incinerated.
Esophageal balloon device
A 15 mL rod-shaped latex balloon with a diameter of 18 mm was connected to the distal end of an enteric catheter (Corpac Medsystems, 10FR, 109 cm). After priming the system with 10 mL of sterile water, the balloon was inserted into the esophagus andthe proximal port of the catheter was connected to a pressure transducer and calibrated using the position ofthe left atrium as a reference. The use of fluoroscopy allowed us to place the balloon at the level of the left atrium. Display of the pressure wave forms with the goal of maximizing the transmitted atrial contraction (a-wave) also aided placement of the balloon. Thereafter, the catheter was connected to a custom-built device that allowed automated pressurization and depressurization of the water-filled balloon via a 19-gauge release valve [Figure 1]. A starting esophageal balloon pressure of 50 mmHg was chosen because it typically exceeds clinically relevant left atrial pressures. This allowed us to record the pressure decay after activation of the release valve while halting the respirator at end expiration. In parallel, left atrial pressures were recorded (LabLink™ Data Interface, Bard Electrophysiology). We hypothesized that the transition point between the initial steep exponential decay and a more linear decay should coincide with the left atrial pressure level. The derivative of a polynominal fitting algorithm allowed us to determine the transition point. The pressure at which the first derivative of the fitting algorithm approached a constant coincides with a visually obtained transition zone as shown in [Figure 2]. The pressures were then correlated to the directly measured mean atrial pressures and a Pearson correlation coefficient was calculated.
|Figure 1: Images of the esophageal pressure balloon with a dimensional reference and automated pressure device|
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|Figure 2: Polynominal fitting of the esophageal pressure decay. The transition from the exponential decay to a more linear decay coincides withthe equilibration pressure. Differentiation facilitates the determination ofthe transition point. In this example the estimated mean left atrial pressure is 10.5 mmHg|
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Transesophageal ultrasound-guided left atrial puncture
We used a clinical endoscopic ultrasound device (Envsion Plus, Dornier Med Tech) equipped with a single-plane ultrasound probe (Olympus GF UC140P-DO5). In contrast to a standard transesophageal echocardiography probe, this device has an additional working channel that allows for the passage of a 22-gauge needle. This system is routinely utilized to obtain mediastinal, lymph node, or lung biopsies.
The ultrasound probe was introduced and advanced into the esophagus. After visualization of the left atrium a 22-gauge biopsy needle (Olympus NA-10J-1) was advanced into the left atrial cavity under ultrasound guidance. The working channel was then connected to a calibrated pressure line to obtain pressure recordings.
| Results|| |
Transesophageal assessment of left atrial pressure
Inflation of the esophageal pressure balloon did not result in any obvious adverse effects. On postmortem inspection of the esophagus, we did not detect any injuries. We also did not encounter esophageal contractions that interfered with our measurements. Two esophageal pressure decay recordings obtained at different pressures are shown in [Figure 3] (Panel A). These recordings demonstrate the effect of atrial pressure on the temporal pressure decay characteristics and also show that transmitted atrial waveforms are maintained throughout the recording.
|Figure 3: Panel (a) depicts esophageal pressure decay and direct atrial pressure recordings at 4 and 17 mmHg, respectively. Increased atrial pressures result in initially steeper and abbreviated pressure decays. The transition point that corresponds to the equilibration pressure was overlaid on the esophageal pressure recording. Panel (b) demonstrated the relation of invasively measured mean atrial pressures and transesophageal pressure estimates|
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We hypothesized that the transition between exponential and linear components of the pressure decay coincides with the left atrial pressure. This transition point reflects a change in pressure decay after pressure equilibration between the left atrium and esophageal fluid volume. We tested this approach by increasing the left atrial pressure with an intravenous fluid challenge followed by aortic ligation. An increase in left atrial pressures steepened and abbreviated the pressure decay. Polynomial fitting as shown in [Figure 2] facilitates automated determination of the transition point. We found that the pressure at which the decay transition occurs is related to the mean left atrial pressure. Panel B of [Figure 3] demonstrates the overall correlation between invasively obtained left atrial mean pressure measurements and transesophageal atrial pressure estimates. Under baseline conditions left atrial pressures were 6.1 ± 0.85 mmHg. This compared to 6.4 ± 1.0 mmHg using the transesophageal pressure estimate. With the fluid challenge and after aortic constriction the pressures were 14.3 ± 1.5 mmHg versus 13.1 ± 1.3 mmHg and 18.5 ± 2.0 mmHg versus 15.6 ± 1.6 mmHg, respectively. The overall correlation coefficient between invasively determined left atrial pressure and transesophageal pressure estimate was r = 0.949. [Figure 4] demonstrates that esophageal transmitted atrial waveforms are largely preserved.
|Figure 4: Left atrial (LA) and transesophageal pressure waveforms. The simultaneous electrocardiographic (ECG) recording is also shown|
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Invasive assessment of left atrial pressure
Left atrial access could be safely established using an ultrasound-guided left atrial puncture. This was accomplished with endoscopic ultrasound equipment that is in clinical use to obtain transesophageal biopsies. The endoscope contains a work channel which can be used to record left atrial pressures. As shown in [Figure 5], direct left atrial pressure recordings and transesophageal pressure recordings obtained through the work channel resulted in similar waveforms and pressures. We also determined that sampling of oxygenated blood from the left atrium is feasible using this approach. This would allow for the assessment of arterial blood oxygen and carbon dioxide levels.
|Figure 5: Direct atrial pressure and invasive transesophageal atrial pressure recording|
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| Discussion|| |
Heart failure is common in critically ill patients and diagnostic modalities for assessing left ventricular filling pressures are currently confined to invasive methods. The routine clinical measurement of left ventricular filling pressures via a central venous access is associated with the risk of complications.  Transesophageal assessments of left ventricular filling pressure do not carry this risk and have therefore clear clinical advantages. Our data from this proof-of-concept study indicates that left atrial pressure assessments from the esophagus are feasible, safe, and reproducible.
Transesophageal left atrial pressure measurement
The transesophageal assessment of left atrial pressures provides a noninvasive approach to assess left ventricular filling pressures. The pressure estimate using the transition point of the pressure decay correlates well with invasive left atrial pressures. This method could conceivably serve as a diagnostic tool to diagnose or exclude heart failure in critically ill patients. This approach may also be useful to direct the care of patients, for example, in the intensive care unit to guide therapy such as fluid administration. As no arterial or venous puncture is required and no indwelling catheters are used, there is no risk of infections and vascular complications.
Conventional methods for the assessment of left atrial pressure and diastolic left ventricular function involve placement of the Swan-Ganz catheter More Details. Other tests that provide insights into left ventricular diastolic function involve the use of echocardiography and determination of brain natriuretic peptides. However, these do not provide a direct pressure assessment. Our approach is unique in that it provides a pressure without the need for vascular access.
This method could also include an atrial waveform analysis. Such an analysis could be helpful to diagnose additional clinically relevant conditions, especially mitral valve disease. Gordon et al. demonstrated this with an esophageal balloon more than 50 years ago.  At the time no attempt was made to estimate left ventricular filling pressures.
We established optimal balloon placement with the use of fluoroscopy and by maximizing the a-wave amplitude. Another approach would be to print distance markers on the catheter similar to the ones on endoscopic probes and catheters. Alternatively, electrodes could be integrated into the catheter or balloon which would allow for an ECG guided placement. Such an electrode equipped esophageal balloon device could also be used for atrial pacing, for example, to terminate atrial flutter or supraventricular tachycardia as previously demonstrated. ,,, Furthermore, direct countercurrent shocks of atrial fibrillation or ventricular fibrillation can be delivered from the esophagus. In patients this was first demonstrated by Zoll in 1952.  Finally, one could incorporate a pressure balloon into current transesophageal echocardiography probe design which would facilitate anatomic positioning and provide complimentary assessments of both hemodynamic and structural information in a single diagnostic examination.
Positional and respiratory changes that change hydrostatic or intrathoracic pressures will undoubtedly have an effect on the recordings. In our experiments, this was overcome by recumbency, sedation, and briefly halting the respirator in end expiration. Similarly, in nonsedated patients, Gordon et al. were able to record high quality transesophageal waveforms during a breath hold.  However, they reported that the presence of the esophageal balloon caused chest discomfort that could not be overcome with the use of topical anesthetics.
Invasive transesophageal left atrial access
Although the indirect transesophageal approach is the main focus of our study we could confirm that the close proximity of the left atrium and the esophagus also allows for invasive access to the cardiac chambers. We are the first to document that direct left atrial pressure recordings can be safely obtained using an endoscopic ultrasound device. Visual inspection of the puncture site in the esophagus revealed a trivial puncture lesion without hematoma or evidence for a fistula. Our review of the endoscopy literature revealed that transesophageal access has been utilized to drain pericardial effusions in at least two patients and to obtain a biopsy of a left atrial mass in one patient using a 19-gauge needle.  No adverse effects were reported. In another animal study in pigs a guidewire was advanced into the left atrium without complications.  In addition, these investigators monitored the animals for 10 days and obtained repeat blood cultures which were all negative. The low risk of infection is also reflected in the general safety of transesophageal mediastinal or pulmonary biopsy procedures. Localized abscess formation or systemic infections are considered to be very rare using this approach. ,
Transesophageal atrial puncture suggests a number of other areas for further investigation. Radiofrequency ablations from the epicardium after entering the pericardial space or from the cardiac cavities appear feasible and have in fact been partially demonstrated in an animal study through the insertion of a radiofrequency ablation needle into the work channel of an endoscopic ultrasound device.  With the advancements and miniaturization in endoscopic and robotic surgery, it is also conceivable that microinvasive mitral valve procedures could be developed.
| Conclusions|| |
Esophageal assessment of the left ventricular filling pressure is feasible and safe and may minimize the need for invasive assessments. The transesophageal route also provides a minimally invasive access site to the heart.
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