Although they did not reach statistical significance, lactate level and dopamine requirement also decreased after the application of TACV (p = 0.052 and p = 0.056, respectively). Chest x-ray revealed improved pulmonary edema after TACV insertion (Figure 3, A and B). In patients 5 and 7, who showed asystole on TTE before TACV insertion, restoration of the arterial blood pressure waveform and heart rhythm on EKG tracing were evident immediately after TACV insertion.
In 1971, Hill et al. 6 reported the first successful use of VA-ECMO in a 24 year-old polytrauma patient with a ruptured aorta. Various types of ECMO pumps and oxygenators have been subsequently developed, enabling the majority of the patients to be stabilized through ECMO support. Thus, VA-ECMO support could reasonably increase mid- to long-term outcome of severe cardiogenic shock, with reported survival rates of 28–42%.7–9 The Extracorporeal Life Support Organization Registry indicates an average survival rate of 41% for adult patients with cardiogenic shock.10
Extracorporeal membrane oxygenation support provides wall tension control and ventricular unloading, as well as ensuring the tissue perfusion.11 However, LV distension occurs and can be aggravated during VA-ECMO by the afterload induced by ECMO on a failing LV, suboptimal venous return with right heart recovery, heavy bronchial and Thebesian blood flow, and aortic insufficiency.11
Inadequate LV decompression during VA-ECMO causes increased LV end-diastolic volume and myocardial wall stress, which lead to increased myocardial oxygen demand and potential ischemic damage to the myocardium.12 Also, elevated left atrial pressure produces pulmonary edema and hemoptysis. Furthermore, there is an increased risk of intracardiac thrombus formation in the distended left heart chamber that shows severe akinesia and a closed AV.13
For these reasons, left heart decompression is of paramount importance during VA-ECMO. However, there is no consensus about the appropriate method or timing of left heart decompression. Although the indication to vent the left heart is still controversial, it is also reasonable to insert a vent prophylactically. Indeed, some centers routinely perform venting before the development of signs of LV distension (e.g., narrow pulse pressure and failure of AV opening in TTE), especially in pediatric patients whose myocardium is extremely vulnerable to distension. Hacking et al. 14 recently reported that prophylactic (elective) left heart decompression in pediatric patients at the time of initiation of VA-ECMO was not associated with improved ECMO survival. According to previous studies on left heart venting, left heart decompression is usually considered in cases of LA/LV dilatation with LV dysfunction or uncontrolled pulmonary edema13,15
There are various methods of venting, including surgical ventricular venting or percutaneous methods of venting. Surgical techniques to directly vent the LV include direct pulmonary venous cannulation and transapical cannulation.13 A number of percutaneous techniques have also been described, including intra-aortic balloon pump, blade or balloon septostomy, axial flow pumps (Impella, Abiomed, Danvers, MA), and a percutaneous transpulmonic approach.13
According to recent articles on percutaneous techniques of venting, the percutaneous transseptal approach is represented to be a more practical and safer method compared with other techniques.16,17 However, left heart decompression using transseptal approaches risks septal injury or possible left-to-right shunt formation. In addition, LA decompression can prevent pulmonary edema but has no direct unloading effect on the LV in the absence of mitral insufficiency, especially in asystole of the LV. Transaortic catheter venting might be advantageous under these conditions because it can directly decompress the LV.
Transaortic catheter venting can be performed percutaneously with TTE, eliminating the need for surgical manipulation, which is associated with bleeding risk and surgical complications. Furthermore, this technique is available at bedside in the ICU, without the need to move critically ill patients. Timely intervention might be impossible if required to be performed in an operating room or catheterization laboratory because LV distension can progress to LV asystole in a few minutes. According to a report by Aiyagari et al.,16 the median procedural time to place the left atrial drain was 51 minutes (range 42–145 minutes). The average duration of the TACV procedure is less than 20 minutes, which is much shorter than that of other techniques. Prompt management of critical patients is possible because of the timely introduction of TACV, which might contribute to better clinical outcome. It is also less expensive than surgical and transseptal approaches.
The TACV catheter can be used to perform blood gas analysis. This allows for early detection of differential hypoxia (especially coronary or cerebral hypoxemia) caused by poor lung function. We performed hourly blood gas analysis from TACV catheter samples. Consequently, we successfully maintained adequate oxygenation in blood ejected from the LV, which is critical for the recovery of damaged myocardium.
There have been several reports about TACV for left heart decompression. In 1997, Kurihara et al. 18,22 reported the effect of TACV on LV function during ECMO. They suggested that TACV might be an adjunctive technique to VA-ECMO for patients with LV failure. However, the study was performed in an adult dog. Whether the results are completely relevant to humans is unclear. Several subsequent human case reports of TACV have been published.5,19 However, no study has addressed the effectiveness of TACV in multiple patients.
To our knowledge, this is the first study regarding the effectiveness of TACV including multiple patients. In addition, we measured the degree of LV decompression using LVEDD as a quantified parameter. The values correlated well with hemodynamic values and clinical resolution of symptoms, such as disappearance of pulmonary edema. In 2014, Weymann et al. 20 reported on the LV unloading effect of central VA-ECMO combined with surgical LV venting in 12 patients. They reported an overall survival rate of 58.3% but did not measure actual hemodynamic parameters of LV decompression. Although we included the small number of patients, the clinical outcomes regarding survival rate and complication rate were notable. Four patients had undergone cardiopulmonary resuscitation before cannulation, which means the underlying pathological process was fulminant. In the previously mentioned setting, four of the seven patients (57%) survived, showing a comparable outcome to previous reports with similar settings. We performed ECMO with TACV without procedure-related complications.
There were some limitations to the current study. First, this was a retrospective study without a control group and included a small number of patients. Consequently, the study has weak statistical power. Further comparison between the TACV and the transseptal approaches will be required. Second, left ventricular end diastolic pressure (LVEDP) is widely used in echocardiographic evaluation of diastolic dysfunction and might be a more accurate index of LV decompression.21 In our study, LVEDD was used as an index of LV decompression in place of LVEDP. However, we were able to confirm a decrease in LVEDP in one case (patient 7) by connecting TACV to a pressure monitoring line. In the future, we will measure LVEDP using a continuous pressure monitor on TACV. Third, we were unable to collect TTE data (e.g., pre-TACV-LVEDD) from deceased patients (patients 1, 2, and 3) because of hemodynamic instability. Last, we could not determine the correct flow through the vent catheter. We could only check the flow patency of the TACV catheter using Doppler ultrasound. Instead, we had to predict the effect of venting as LVEDD according to TTE before and after the procedure.
In conclusion, TACV is an easy, rapid, and safe method for direct LV decompression. It is useful especially in emergency cases in which surgical venting or complex procedures are not possible. Transaortic catheter venting is a feasible option for LV venting, especially in patients with LV distension with asystole or severe LV dysfunction.
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Keywords:Copyright © 2016 by the American Society for Artificial Internal Organs
extracorporeal membrane oxygenation; decompression; left ventricular dysfunction