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Catheter ablation for treatment of ventricular tachycardia (VT) may be performed using 2 different ablation strategies. Substrate-based mapping targets the putative channels for VT that can be identified during sinus rhythm. This is an effective strategy in patients with ischemic cardiomyopathy where complex fractionated electrograms, late potentials, and local abnormal ventricular activities can be targeted in sinus rhythm.1 However, in patients with nonischemic cardiomyopathy, there is a relative paucity of these targets, thereby rendering this strategy significantly less effective.² The second strategy involves entrainment and activation mapping with identification and ablation of the critical isthmus for VT.³ This may be the preferred strategy when the potential VT circuits are adjacent to critical anatomical structures such as the coronary artery or phrenic nerve where an extensive substrate-based ablation may be suboptimal due to the potential for collateral damage (Figure 58.1). However, hemodynamic instability during episodes of VT often precludes detailed mapping. Even repetitive brief episodes of unstable VT may negatively affect end-organ perfusion and result in hemodynamic decompensation. Vasopressors or inotropes may be used, but the extent of hemodynamic support provided is usually inadequate. Prolonged use of these agents may also be cardiotoxic, with increased risk for multi-organ dysfunction, morbidity, and mortality. Use of temporary mechanical circulatory support devices is an attractive strategy for activation and entrainment mapping of hemodynamically unstable VT.

Patient Selection

The decision regarding the need for mechanical support should be based on the patient’s cardiac status, including heart failure functional class and systolic function, the cycle length of clinical and inducible VTs, hemodynamic status during VT, myocardial substrate for VT, prior catheter ablations and reasons for prior ablation failure (such as inadequate activation/entrainment mapping due to hemodynamic intolerance), and the depth of anesthesia. While hemodynamic support may be beneficial in both ischemic and nonischemic cardiomyopathy, the benefit may be greater in patients with nonischemic cardiomyopathy where substrate-based ablation is less effective. Patients with nondilated left ventricle (LV) or significant LV hypertrophy are less likely to benefit from percutaneous LV assist device (pLVAD) such as Impella (Abiomed, Danvers, MA). Furthermore, pLVADs should be avoided in patients with disproportionately severe right ventricular dysfunction or advanced pulmonary hypertension, as they may demonstrate worsening of their hemodynamic profile with pLVADs. Due to direct unloading of the LV, the Impella device is more efficient in reducing LV end-diastolic pressure and myocardial oxygen demand compared to the TandemHeart (CardiacAssist, Inc., Pittsburgh, PA) at comparable flow rates. Furthermore, Impella requires smaller arterial sheaths and obviates the need for additional venous access and transeptal puncture, which may potentially reduce complications and shorten implantation times. In our center, Impella is therefore the preferred device for hemodynamic support for VT ablation. In cases where retrograde aortic approach is used for LV mapping, TandemHeart is preferred.

Table 57.1 provides a comparison of commonly used percutaneous hemodynamic support devices for VT ablation.

Table 57.1 Percutaneous hemodynamic support devices

The benefits of the intra-aortic balloon pump (IABP) are its relatively small arterial sheath size (7.5- to 8-Fr), ease of insertion, and familiarity to lab personnel. The balloon is positioned in the descending aorta, with the distal end of the balloon lying a few centimeters distal to the origin of left subclavian artery and the proximal end above the renal arteries. Decrease in afterload by balloon inflation in systole augments LV performance. Inflation of the balloon in diastole augments the diastolic pressure and improves coronary and peripheral blood flow. Though IABP is widely used for hemodynamic support in cardiogenic shock, this is not ideally suited for patients undergoing VT ablation as this requires a stable, regular, and nontachycardic rhythm. Furthermore, IABP augments cardiac output only by 0.5 L/min, which may not provide adequate support during VT ablation. Optimal functioning of the IABP is dependent on timing of balloon inflation and deflation to pressure- or ECG-based triggers. Synchronization trigger used for balloon inflation during VT ablation should be either a “peak of QRS” trigger on surface ECG or arterial pressure waveform trigger. At our centers, we rarely use IABP support due to the minimal amount of hemodynamic support provided during VT.

The pLVAD implant technique for patients undergoing VT ablation is as follows.4 Percutaneous vascular access is obtained in the (usually left) common femoral artery with care to ensure that the puncture is above the level of femoral artery bifurcation. Contrast is administered to ensure the level of access and to rule out significant peripheral arterial disease. The arteriotomy tract is then dilated with a 6- to 8.5-Fr sheath. Prior to upsizing to the 13-Fr or 14-Fr sheath, “preclosure” of the arteriotomy is performed using 2 orthogonally placed 6-Fr Perclose vascular closure devices (Abbott Vascular, Redwood City, CA). “Preclosure” helps with rapid hemostasis after removal of the arterial sheath at the end of the procedure. After upsizing the sheath to the final large-bore introducer needed to accommodate the pLVAD system, anticoagulation with intravenous heparin is initiated to achieve target ACT of greater than 250 seconds (Figure 57.2). The pLVAD is advanced retrograde through the aorta over a 0.018-inch guidewire (inserted through JR4, AL-1, multipurpose or pigtail catheters), and across the aortic valve such that the inlet of the device is positioned in the LV approximately 4 cm below the aortic valve annulus, with the outlet in the aortic root. Figure 57.3 is an example of an attempt to insert the Impella CP across the aortic valve without the use of a guidewire, followed by successful implantation with the over-the-wire technique ( Video 57.1). After confirming the appropriate positioning of the device with fluoroscopy and intracardiac echocardiography, the device is turned on and titrated up to its full support capability. Proper device positioning should then be reconfirmed using the positioning waveform on the console. As the device position may change during episodes of VT or after abrupt termination of tachycardia, the positioning of the device should be monitored throughout the procedure, and can typically be corrected with minor manipulation of the shaft at the level of the femoral access sheath.

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