TMR is an approved surgical procedure for diffuse, end-stage coronary artery disease either as a stand-alone procedure in patients with medically refractory angina who are not candidates for further conventional revascularization procedures or in conjunction with CABG in patients who would be incompletely revascularized by CABG alone.1–3 Once a reasonably popular procedure, TMR has received renewed interest in recent years. According to the Society of Thoracic Surgery database, 24,809 TMR procedures were performed nationwide in Society of Thoracic Surgery participating centers from January 2002 to December 2012.a
The procedure entails creation of 1-mm laser channels in the myocardium that presumably induce neovascularization, particularly at the junction of the channels and the myocardium over the ensuing 3 to 6 months.4 Relief of anginal symptoms may also be due to ablation of sympathetic neurons supplying the myocardium.5 When used along with CABG, TMR is usually done after CABG while still on CPB.
Several different lasers have been used in the past, but only Ho:YAG and carbon dioxide (CO2) lasers are Food and Drug Administration approved for this purpose (Table 1). TEE plays an important role in guiding this procedure. When TMR is done as a stand-alone procedure, a comprehensive TEE examination (Table 2) should precede it to assess ventricular function and to document any preexisting RWMAs, valvular dysfunctions, and pericardial effusion. It is also important to diagnose intracardiac thrombus or air, because this could lead to systemic embolization during TMR. For this, the left atrial appendage should be interrogated in multiple zoomed midesophageal views at increments of 30° to 40º starting from the 4C at 0º with moderate anteflexion until the entire appendage is visualized. LV apical thrombus must also be excluded, by scanning it in the midesophageal 4C, 2-chamber, mitral commissural, and LV long-axis views, making sure to avoid any foreshortening of the LV apex.
When the channels are created, the laser energy is absorbed by the blood, and a blast of steam (sometimes referred as a “puff of smoke” or “fireworks”) appears in the LV on TEE, signifying transmural penetration of the laser. However, absence of the “blast of steam” implies inadequate penetration, which can be communicated to the surgeon. In our experience, a 4C or 5C view allows visualization of the unique acoustic effect created by channels anywhere in the LV, including the inferior wall. Unlike CO2 lasers, for which TEE is mandatory to confirm transmural penetration, Ho:YAG lasers provide the surgeon with adequate tactile and auditory indications when the laser has completely channeled through the myocardium into the LV.1 Placement of the probe distorts the LV. An approximate position of the probe in relation to the important cardiac structures such as the mitral and aortic valves as well as the conduction system near the atrioventricular groove can be estimated, and this can be communicated to the surgeon before the laser is even fired. Though not essential, the authors prefer 3D over 2D TEE as it allows better localization of the origin of the blast of steam, enabling better collaboration with the surgeon. During the procedure, however, 3D TEE is limited to Live 3D TEE rather than full volumes, especially in the presence of arrythmia. Consequently, volume rates may be suboptimal if the intention is to view a large pyramidal volume of data such as the entire LV. A thorough post-TMR, 2D, and 3D TEE along with color flow mapping should be done to check for injuries that may manifest as a new or worsening mitral or aortic regurgitation. Also, any new RWMAs should be assessed in transgastric basal, mid-short-axis, and apical views. Although bleeding from the epicardial surfaces often stops quickly, the TEE examination should include an examination for pericardial effusions that can occasionally result from such bleeding.
There is a propensity toward atrial and ventricular arrhythmias during and immediately after the procedure. Invariably, there is a transient injury pattern, with ST elevations that usually resolve spontaneously. On occasion, however, TMR can cause large areas of myocardial infarctions with subsequent ventricular dysfunction.6
In summary, 2D and 3D TEE imaging modalities are useful in collaborating with the surgeon during the TMR as well as to monitor for potential complications inherent to the procedure.
Clinicians Key Teaching Points
By Roman M. Sniecinski, MD, Donald Oxorn, MD, and Martin J. London MD
- Based on the reptilian heart, where the ventricles are perfused via a diffuse network of sinusoids, transmyocardial revascularization (TMR) creates microchannels in the myocardium by using a laser. It may offer symptomatic relief from refractory angina in patients who have no other options for revascularization procedures. During TMR, a cloud of bubbles (termed a blast of steam in this report) is seen on transesophageal echocardiography (TEE) when the laser traverses the full thickness of myocardium; this through-and-through penetration is thought to be necessary for clinical benefit.
- A comprehensive TEE examination should be performed at baseline, focusing on any valvular disease or regional wall motion abnormalities that may be exacerbated during the procedure. The presence of thrombus in the left atrial appendage or left ventricular apex should also be excluded due to embolization risk.
- In this case, the authors used both 2 dimensional (D) and live 3D TEE to confirm when transmural penetration had taken place by visualizing the cloud of bubbles. The 4- and 5-chamber views were used to ensure no damage occurred to the aortic or mitral valves from the laser. While bleeding from the resulting channels typically stops before chest closure, TEE is also useful to monitor for any resulting pericardial effusion.
- Cardiac surgeons may choose to perform TMR when there are no suitable targets for conventional revascularization. The intraoperative echocardiographer should be aware that TEE can provide useful information before, during, and after the procedure.
Name: Shvetank Agarwal, MD.
Contribution: This author wrote the manuscript, designed the case-report, and acquired and interpreted TEE images and video loops.
Attestation: Shvetank Agarwal approved the final manuscript.
Name: M. Vinayak Kamath, MD.
Contribution: This author helped write the manuscript.
Attestation: M. Vinayak Kamath approved the final manuscript.
Name: Manuel R. Castresana, MD.
Contribution: This author helped write the manuscript.
Attestation: Manuel R. Castresana approved the final manuscript.
This manuscript was handled by: Martin J. London, MD.
We thank Nadine Odo for editing the manuscript.
a 2013 Harvest 1-Executive Summary Adult Cardiac Surgery Database. Available at: http://www.sts.org/sts-national-database/database-managers/executive-summaries. Accessed August 30, 2013.
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