Acute Myocardial Infarction with Cardiogenic Shock: Time for a Paradigm Shift in Care
Despite advancements in clinical care, pharmacologic technology, and streamlined access to primary PCI centers in much of the United States, the mortality rate of acute MI patients presenting in cardiogenic shock here has plateaued after an initial decline in the 1990s. Additionally, there are NCDR registry data to further suggest that those who survive to hospital discharge are exposed to ongoing hazards.
As interventional fellows, we are training in an era of more complex patients and rapid technological advancements. Understanding the current challenges and developing the cognitive and procedural skills to treat these patients is essential for the toolkit of every fellow.
We should, as a collaborative community, develop a consensus on how these patients ought to be evaluated and treated. Here are a few ways in which we can improve upon the care delivery to these critically ill patients.
1. Recognize cardiogenic shock
Despite the standardized definition of cardiogenic shock used in the 1999 SHOCK trial, there remains interphysician variability in identifying shock patients. Cardiogenic shock is defined as systolic blood pressure < 90 mm Hg (or > 90 mm Hg on inotropic support), evidence of end-organ hypoperfusion or a cardiac index < 1.8 L/min/m2 (or < 2.2 L/min/m2 on ionotropic support), and a pulmonary capillary wedge pressure > 15 mm Hg. Patients with overt presentations of shock and/or acute MI-related circulatory arrest are easily identifiable. However, what clinicians do with the information is another matter. Institutional resources, clinical context, and the procedural skill set of the interventional operator all play into the management strategy employed. Furthermore, subtle presentations can be challenging to identify as certain patients may have noninvasive hemodynamic parameters near normal and thus require a closer look with invasive measures. These patients may stand to benefit the most because timely recognition and treatment of cardiogenic shock is linked to survival. A quick-focused transthoracic echocardiogram at the bedside to assess LV systolic function, basic cardiac structure, and the pericardial space can be an indispensable tool in rapidly forming a treatment strategy upon arrival to the cath lab. Although right heart catheterization for acute MI patients with cardiogenic shock is not routinely recommended per American College of Cardiology/American Heart Association guidelines, invasive hemodynamics can be helpful in recognizing cases such as patients with baseline LV dysfunction who present with a mild MI but have extreme hemodynamic compromise due to low reserve.
2. Identify concomitant RV failure
Traditionally, the management of this patient subset has been heavily centered on LV function assessment and support. However, it is equally crucial to identify the presence of concurrent RV failure. The pulmonary artery pulsatility index can be a helpful tool in identifying high risk patients with inferior wall acute MI and RV systolic dysfunction. The assessment of right heart pressures after the appropriate consideration of LV support and culprit-vessel revascularization may help identify cardiogenic shock patients presenting with simultaneous RV failure. These patients with acute biventricular failure may warrant a percutaneous assist device for both ventricles prior to departure from the cath lab. Therefore, recognizing that many acute MI shock patients do not necessarily present with isolated LV failure is crucial in uncovering who may stand to benefit from timely biventricular support.
3. Think about access routes
Historically, patients presenting with acute MI and cardiogenic shock have been triaged to femoral access and potentially bifemoral arterial access if a hemodynamic support device is placed on the contralateral side. However, transradial PCI allows for sparing of one of the femoral access points and saves unilateral femoral access for a support device as needed. Additionally, with the radial approach the operator can quickly advance a 125-cm pigtail catheter into the distal infra-renal abdominal aorta for bilateral aortoiliac angiography and quick visual assessment of aortoiliac vessel size and tortuosity. With this road map, it’s possible to devise a plan for access side and type of LV assist device. Overall, it is important to keep in mind that shock patients present with multiorgan dysfunction and coagulopathy and that less reliance on femoral access can translate into fewer major vascular complications.
4. Know that time-to-implant of LV support is as crucial as D2B time
Traditional dogma once dictated that we open the infarct artery first, and oftentimes solely, when managing acute MI patients with shock. Our knowledge and clinical practice has certainly come a long way since that time, and interventional fellows now have access to several commercially-available percutaneous ventricular assist device (pVAD) options. Although pVADs and extracorporeal membrane oxygenation (ECMO) have not been shown to definitively improve survival in acute MI patients with shock, they have been shown to improve end-organ perfusion, decrease blood lactic acid concentration, and effectively unload the ventricle irrespective of residual native ventricular function or underlying rhythm. Each pVAD has its own nuances of implantation (ie, trans-septal puncture, large bore femoral arterial-venous access) and provides enhanced hemodynamic support above and beyond the capabilities of the intra-aortic balloon pump. As fellows, we ought to starting thinking about ‘time-to-implantation’ of an indicated and appropriate pVAD being as crucial as opening the infarct artery; the concept of ventricular and global organ rescue is as central of a priority as restoring coronary flow. Acute MI with cardiogenic shock is not simply a one-dimensional problem of an occluded coronary artery.
5. Create regional “shock centers” and an algorithmic approach to care
Pragmatically, not every hospital can be a referral center or center of excellence for acute MI patients in cardiogenic shock given the breadth of resources needed to support such titles. However, this reality is juxtaposed against the truth that the majority of acute MI patients with shock initially present to local community hospitals. To make matters worse, pVADs and the clinical support staff to manage these devices are not ubiquitously available. As such, we need statewide systems to designate regional shock and cardiac arrest centers so that patients have access to trained clinicians, nurses, and cath lab staff when they present in extremis. At the same time, efforts need to be made to make pVADs more widely available to primary PCI centers. An algorithmic and team-based approach to care can help provide an educational and training framework for staff and first responders. Lastly, presentations of shock can initially be nondescript and due to a myriad of differential diagnoses, therefore designated “shock centers” must also be equipped to manage the patients with other forms of systemic shock who need critical care.