|29||Surgical Epicardial Ablation|
|Jackson J. Liang, DO; Sanjay Dixit, MD|
Open-heart surgery for ventricular tachycardia (VT) has been performed since the 1950s.1 Initially, VT surgery was performed primarily in patients with aneurysm due to myocardial infarction, in whom surgical aneurysmectomy and/or endocardial resection was performed guided by visualization of scar in the operating room by the surgeon.2,3 Outcomes using this approach, however, were suboptimal with relatively high VT recurrence rates of over 40%.4 Success rates of surgical endocardial resection subsequently increased significantly after intraoperative electrophysiologic mapping began being used to guide ablation.5,6 However, due to the highly invasive nature of the procedure, VT surgery was never widely adopted. With the advent of percutaneous catheter ablation techniques, the utility of surgical VT ablation has declined even further, and nowadays it is considered in very infrequent scenarios. In this review, we will discuss the current practice of surgical VT ablation.
INDICATIONS FOR SURGICAL EPICARDIAL ABLATION
At present, surgical VT ablation is usually reserved for patients in whom catheter ablation has failed due to anatomic constraints (i.e., midmyocardial or septal substrate not amenable to ablation from endocardial and epicardial approach or proximity of critical VT components to epicardial coronary arteries). Surgical ablation is also occasionally performed in patients with dual mechanical aortic and mitral valves, which can preclude adequate access to the left ventricle (LV). Surgical VT ablation is utilized in cases where percutaneous epicardial access is challenging, such as in patients with prior cardiac surgery and/or patients that may have undergone prior epicardial VT ablation attempts, or those with a history of pericarditis. In the latter scenarios, even though access to the pericardial space may be obtained, catheter manipulation to different parts of the epicardial surface of the heart may be limited due to the presence of dense pericardial adhesions. Another indication for surgical ablation is in patients with ventricular arrhythmias who are undergoing cardiac surgery for other reasons, that is, patients with VT undergoing coronary artery bypass grafting (CABG), valve surgery, or left ventricular assist device (LVAD) implantation. Finally, surgical ablation should be considered in patients who are brought to the operating room for emergent surgical management of complications during attempted percutaneous VT ablation.
Surgical Access to the Epicardial Space
In order to maximize procedural success, adequate access to the surfaces of the heart harboring the suspected VT substrate is necessary. If the VT substrate is suspected to be epicardial then various approaches can be utilized to expose this location.7 Less invasive approaches are undertaken via creation of surgical window either through the subxiphoid location (through an epigastric incision with or without removal of xiphoid process) or by means of a left anterior thoracotomy (left anterior incision from third to fifth intercostal spaces). These surgical approaches are relatively straightforward and can be performed by the surgeon in the electrophysiology laboratory itself. Epicardial visualization using these less invasive surgical approaches, however, is limited to the inferior epicardial aspect of the left and right ventricles and some parts of the anterior and lateral LV epicardium.
Median sternotomy is a more invasive approach, but provides the best visualization and access to all surfaces of the heart (Figure 29.1, Panel A). The RV free wall, anterior, anterolateral, and apical LV, and superior aspect of the interventricular septum can all be readily visualized with median sternotomy without the need for significant cardiac manipulation. However, in order to fully visualize the posterolateral and posterior LV wall, the heart must be lifted, which usually results in transient but profound hypotension due to reduction of cardiac output.8 To improve visualization of the posterolateral LV, repeated, transient induction of apnea can also be utilized.
Figure 29.1 Techniques to expose various cardiac surfaces during surgical VT ablation Panel A: Cardiac exposure via median sternotomy. Panel B: Transaortic access to LV endocardium. Panel C: Access to the LV endocardium through the cored out apex at time of left ventricular assist device placement.
Surgical Access to the Endocardial Aspect of the Ventricles
Visualizing the LV endocardium requires additional myocardial resection. Different approaches to access to the LV endocardium can be used, depending on the region of suspected VT substrate and/or site of origin. A transaortic approach via standard aortotomy above the sinotubular junction (as typically performed for aortic valve replacement) provides optimal exposure of the LVOT region; the basal, anterior, and lateral LV walls; as well as the interventricular septum (Figure 29.1, Panel B; Video 29.1).8,9 On the other hand, a transatrial, transmitral valvular approach may better expose the LV papillary muscles, posterior LV endocardium, and the LV apex.8,10 Access via an apical ventriculotomy can also be used to access the LV and is often utilized in patients with dual mechanical aortic and mitral valves, or in patients in whom concomitant LVAD implantation is being performed (through the LV apical core at the LVAD implantation site; see Figure 29.1, Panel C; Video 29.2).
The RV can be accessed either transatrially (via right atriotomy and traversing the tricuspid valve) or directly via RV free wall ventriculotomy.8,11 Importantly, a less invasive partial sternotomy (sparing the upper half of the sternum) may be adequate to achieve access in patients in whom the VT substrate is limited to the RV free wall or inferior interventricular septum.12
MAPPING AND ABLATION IN THE OPERATING ROOM
VT mapping in the operating room was initially performed using finger-mounted bipolar electrodes, which were moved to different locations in the chamber of interest. Subsequently, multipolar meshes and basket catheters became available, which permitted recording of electrograms from several sites simultaneously with increased resolution. Now, with the advent of 3D electroanatomic mapping (EAM) systems and multielectrode mapping catheters, detailed EAMs can be created with relative ease in the operating room setting. EAM requires the placement of a magnet underneath the operating table and reference electrodes, which can be sutured to the epicardial surface of the exposed surface of the heart after sternotomy.
Detailed mapping (activation and/or entrainment) requires sustained VT; however, this can be difficult in the operating room setting for multiple reasons. Patients in the operating room are under general anesthesia, which can diminish the inducibility of VT. Furthermore, if cardiopulmonary bypass is utilized, then this can alter cardiac filling, which can attenuate VT induction. Additionally, the use of cold cardioplegia can further reduce the inducibility of VT. As such, surgical VT ablation in the operating room in patients in whom the clinical arrhythmia cannot be induced is often guided by electrophysiologic findings from prior percutaneous catheter ablation attempts. We have previously described our experience of surgical cryoablation after prior percutaneous attempts at mapping and catheter ablation.13,14 In the majority of these cases, detailed endocardial (and epicardial, when indicated) activation and entrainment mapping was performed in the EP laboratory prior to surgical ablation. This allowed for identification and localization of critical VT components—entrance, exit, and isthmus sites—that were targeted with radiofrequency catheter ablation. While radiofrequency ablation was not always successful in eliminating VT, these lesions (especially on the endocardium) could be visualized in the operating room and served as targets for cryoenergy application in order to achieve successful surgical ablation (Figure 29.2).
Figure 29.2 Visualizing radiofrequency ablation lesions at time of surgery. Radiofrequency lesions delivered at a prior percutaneous catheter ablation attempt seen in the LV endocardium can be used to guide surgical ablation.
This approach precluded the need for additional arrhythmia induction or mapping during open-heart surgical ablation. In the operating room, effective lesion creation for these cases was achieved by placing the cryoprobe over the radiofrequency (RF) lesion site and delivering cryothermy for up to 3 minutes (including both the cooling and the thawing phase) with a target temperature drop to −140° C. The latter requires cold cardioplegia and typically resulted in a sizable lesion, the induration from which could be palpated on the opposing surface (Figure 29.3).