Abstract
To the Editors,
We read with great interest the recent report from Tsilimparis et al, 1 in which a modified Valsalva maneuver has been described in patients undergoing a triple-branch thoracic endovascular aortic repair (TEVAR). The authors must be commended for highlighting the importance of the cardiac output reduction strategies to achieve accurate stent-graft positioning, which requires a constant low blood pressure with no systolic ejection. Pharmacological agents (antihypertensive drugs, nitroglycerin, adenosine), mechanical methods (temporary caval occlusion by balloon, proximal aortic balloon occlusion), and rapid right ventricular pacing (RRVP) have been proposed to overcome the “windsock effect” during endovascular surgery. Nevertheless, only few studies have compared these different techniques. Neinaber et al, 2 in a retrospective analysis on 70 patients undergoing TEVAR, reported that the RRVP (160–200 beats/min) was superior to adenosine (0.5 mg/kg in bolus) and nitroprussiate (5 µg/kg bolus and 3 µg/kg/min continuous infusion) in onset and offset of the induced hypotension and endograft landing precision. Notably, the 3 approaches were equally safety with no neurological sequelae. Bernad et al 3 showed that nitroglycerin (cumulative dose 50–250 µg), was effective in achieving a rapid and brief (1–4 minutes) decrease of blood pressure (60–90 mm Hg) during the stent-graft procedure, with no side effects. Similarly, adenosine, which induces rapid and temporary profound atrioventricular block, has been purposed as attractive pharmacological method of pressure reduction. In the study by Kahn et al, 4 for instance, a high dose of adenosine (24–90 mg) was safe and allowed a more precise release of a balloon-deployed stent-graft in abdominal aorta. However, in 6% of cases cardioversion for atrial fibrillation or brief activation of the temporary pacemaker was required. 4 In addition, in patients with bronco-reactivity, adenosine should be administered with caution due to the anecdotal experience of intraprocedural bronchospasm. 5 Taking together the above considerations, the major drawbacks of the pharmacological strategies can be summarized in inability to control duration and extent of hypotension, interpatient dose variability, and development of tolerance. Thus, the use of “mechanical strategies” for deliberated hypotension, acting selectively on preload and contractility have a theoretically more favorable hemodynamic profile compared with the use of systemic drugs. In fact, the cornerstone of the cardiac output reduction techniques is not the hypotension itself but the reduction of stroke volume and consequentially of the aortic flow in order to mitigate the risk of stent-graft malpositioning. For example, the application of a balloon partial occlusion of the inferior vena cava, reducing the preload, permits to achieve and maintain a lower target pressure for a longer time with a faster hemodynamic recovery compared to pharmacological strategies. Nevertheless, the use of transesophageal echocardiography, and therefore of general anesthesia, is strongly recommended to evaluate balloon position and cardiac stress.
Hence, the most used and applied method is the RRVP 6 that, by a progressive acceleration of the heart rate, reduces intra-aortic blood flow permitting a more precise graft deployment potentially lowering the incidence of endoleaks and distal migrations. The rapid onset and offset of action on patient’s hemodynamic can shorten the duration of the procedure and allows minimal sedation. 7 Both aspects are not elusive in individuals with poor clinical status and at high risk for spinal cord ischemia. Most complications are puncture-related which are dramatically dropped after the wide adoption of an ultrasound guided femoral vessels cannulation. Rhythm-associated complications can occur in patients with heart diseases and are usually managed with a prompt defibrillation. The incidence of ventricular fibrillation after RRVP for transfemoral aortic valve replacement is 2% to 3% 8 and rarely, cardiovascular collapse requiring cardiopulmonary bypass and deaths have been reported during transcatheter aortic valve replacement (TAVR) and TEVAR. 9 Nonetheless, several studies suggest that RRVP may have deleterious effect on the myocardium, temporary affecting right and left ventricular systolic and diastolic function, impairing both myocardial macro- and micro-circulation. 10 Therefore, RRVP should be used cautiously, limiting duration and number of pacing episodes in patients with impaired myocardial reserve, or poor tolerance to tachycardia (ie, severe coronary artery diastolic dysfunction, or hypertrophic cardiomyopathy). In these settings, temporary caval occlusion by balloon might be a good alternative; however, few studies have analyzed the possible contraindications and associated complications. In the authors’ experience, RRVP with a transvenous pacing wire floated from the femoral vein is the strategy of choice, 11 being applicable even in mild sedated patients with limited cardiopulmonary reserve. Nevertheless, we recognize that this approach is relatively resource consuming requiring a well-trained team and the presence of an anesthesiologist with advance skills in echocardiography (transthoracic and transesophageal). In fact, in the event of persistent hypotension after RRVP only the echocardiography allows to rule out if the hemodynamic instability depends on pericardial effusion, myocardial stunning, cardiogenic shock, low preload, or afterload.
Interestingly, the use of a Valsalva maneuver has never been investigated previously in this setting. Nevertheless, several considerations are required before a routine use of MuVIT. First, high-risk surgical candidates undergoing an endovascular treatment should be best treated under local anesthesia and the latter is even not required in complex endovascular treatments that can be performed transfemorally. 12 These patients may benefit of sedation, which allow a more stable hemodynamic profile and continuous neurological evaluation. Even when the general anesthesia remains the only option (noncollaborative patient, surgical access, or prolonged procedure), the attending anesthesiologist may prefer to use a laryngeal mask rather than the orotrachel tube to avoid curarization and the inherent risks associated with intubation. Therefore, in these cases, it is impossible to perform a Valsalva maneuver effective to decreasing cardiac output. Second, the disconnection from mechanical ventilation may be indicated to enable precise thoracic endograft deployment along with a good quality angiography. Last, the Valsalva maneuver is challenging for heart and lung. For the latter, the acute rise of the plateau pressures may generate barotrauma and pneumothorax, especially in noncompliant lungs, even when applied for a short period of time. From the former, it is well known that direct compression of the lung volume on the cardiac fossa, with subsequent increase in juxtacardiac pressure, decreases the right ventricular (RV) preload (venous return), increases the RV afterload (pulmonary vascular resistance), and may produce LV impairment due to a leftward displacement of the interventricular septum (ventricular interdependence). In practice, patients with limited cardiovascular and pulmonary reserve are at higher risk of developing complications during the MuVIT protocol. Until new evidence becomes available, MUVIT may be suitable in relatively healthy patients undergoing general anesthesia. Future studies should be focused on the determination of the best positive end expiratory pressure to have the maximum hypotensive effect at the lowest cost for heart and lungs.
We thank the authors for their interesting report, and we hope more will follow, proving the superiority of the MuVit strategy in terms of safety and outcome, while carefully considering the risk for pulmonary and cardiac impairment. Further investigations are needed to compare the different cardiac output reduction methods to refine their indications and highlight possible drawbacks.
