Cardiogenic shock represents a dynamic set of conditions, presentation profiles and pathophysiologic mechanisms whose mortality has not changed in more than 20 years. While almost 75 percent is due to predominant left ventricular failure, a quarter is due to something else, such as a rupture or tamponade, right ventricle shock or acute severe mitral regurgitation.
“The reality is all shock is not created equal,” says Shelley Hall, MD, FACC, FHFSA, FAST, Chief, Transplant Cardiology, Mechanical Circulatory Support and Advanced Heart Failure, Baylor University Medical Center, part of Baylor Scott & White Health. “The etiology and acuity of the shock state are incredibly important in determining how the condition is treated. Our failure to appreciate that over the past two decades has somewhat hampered our ability to make advances in our understanding and treatment of shock.”
Unlike most other disease entities, cardiogenic shock is also defined by the same language that was in use more than 20 years ago. The Society for Cardiovascular Angiography & Interventions (SCAI) published a Clinical Expert Consensus Statement on the Classification of Cardiogenic Shock in 2019. To develop this terminology, SCAI brought together a variety of specialties from many different organizations, including interventional cardiology, heart failure, critical care, emergency medicine, cardiac surgery and nursing. Dr. Hall was part of this committee as a representative of the Heart Failure Society of America. This staged terminology has ultimately been endorsed by nearly all the five major cardiac societies and is currently undergoing an update with refinements based on the past two years.
|SCAI Stages of Cardiogenic Shock|
|Stage A||At Risk|
A patient with risk factors for cardiogenic shock who is not currently experiencing signs or symptoms. The shock team needs to be alert to signs of deterioration.
A patient who has clinical evidence of relative hypotension or tachycardia without hypoperfusion. The patient is starting to experience hemodynamic changes, yet still feels warm, well perfused.
A patient presenting with hypoperfusion requiring intervention beyond volume resuscitation (inotrope, pressor, or mechanical support, including ECMO).
A patient who fails to respond to initial interventions (multiple pressors or temporary mechanical support). Similar to Stage C but getting worse.
A patient being supported by multiple interventions who may be experiencing cardiac arrest or recurrent arrhythmias with ongoing CPR and/or ECMO.
“In diagnosing classic shock, you must have both inadequate cardiac output and hypoperfusion of other organs,” Dr. Hall says. “Acute chronic heart failure patients have inadequate cardiac output all the time, but their bodies have adapted. This is when biomarkers and historical labs become important. If a patient’s creatinine is always at 2.0, it’s not necessarily hypoperfusion. But if the patient’s normal creatinine is 0.8 and he or she comes in with a creatinine of 2.0, then we know something is happening.”
Several recent studies have validated the utility of these stages in predicting outcomes. A retrospective study looked at more than 10,000 patients in the cardiac intensive care unit over a 10- to 11-year period. The results found a direct correlation between ICU and total hospital mortality: the worse the stage, the greater the mortality (J Am. Coll Cardiol 2019). A prospective validation of the SCAI shock classifications by David A. Baran, MD, FACC, FSCAI, FHFSA was published Oct 7, 2020. This single center analysis looked at 166 patients and again found a correlation related to severity. The worse the SCAI shock category, the less likely they were going to survive.
“What is particularly interesting is the 24-hour response,” Dr. Hall says. “If they improved their SCAI stage in the first 24 hours, then they had excellent outcomes with nearly 80 percent survival. If they failed to respond or improve or got worse, then there were very poor outcomes. These data give us the beginnings of real potential trial design and analysis for cardiogenic shock.”
Identifying cardiogenic shock
Despite the availability of data used to develop the SCAI shock classification, identifying patients with shock can be a challenge. Physical exam findings are not particularly helpful, no matter how skilled the physician or nurse assessing the patient. However, some lab results can be very useful. A mixed venous blood gas drawn from a central line or PICC line can indicate how low the cardiac index is before starting inotropes. In addition, multiple studies have validated the importance of lactate, which reflects poor tissue perfusion. If a patient’s lactate levels can be brought down to the 2-4 range within 24 hours, he or she is much more likely to survive. If the lactate level stays elevated and tissue perfusion does not improve despite interventions, the patient is less likely to survive.
Ultimately, identification of cardiogenic shock falls to hemodynamic data derived from placement of a Swan-Ganz catheter. Hemodynamic assessment is critical for making decisions on the severity of the shock, as well as determining the right support for the right patient as quickly as possible.
“We need better understanding of the importance of the Swan,” Dr. Hall says. “The reality is indiscriminate use of the Swan is not effective, but cardiogenic shock by its very nature is a Class 1 indication since the 2013 ACC/AHA heart failure guidelines. The guidelines tell us to use it, but, as a group, clinicians are not using it effectively or frequently enough.”
Treating cardiogenic shock
The treatment of cardiogenic shock has two goals: to restore adequate end-organ perfusion before patients reach the vasodilatory SIRS response where it is almost too late to save them and to unload the ventricle to save cardiac muscle, especially when dealing with acute myocardial infarction. The goal of any medical therapy should be to optimize perfusion while limiting the toxicity of the particular drugs being used.
“While we don’t have the ideal drug to treat cardiogenic shock, inotropes, vasopressors and vasodilators all have their role when used correctly,” Dr. Hall says. “So again, hemodynamic monitoring with a Swan is integral to titrating these drips if you’re going to have any success at all with them.”
Fortunately, many different devices are available to try to help patients who do not respond to first-line medications. These devices include the intra-aortic balloon pump (IABP), TandemHeart®, Impella® and veno-arterial ECMO. Each device has different mechanisms of operation, variable cost and its own set of pros and cons.
“Despite our progress in the management of cardiogenic shock, which mechanical circulatory support therapy to use and when to use it remains a challenge,” Dr. Hall says. “To date, no trials have demonstrated one device is superior to the other or the most appropriate time to use it. This is where we hope the SCAI shock language will help us design such trials.
“Shock patients are very sick, complicated patients. The more mechanical circulatory support that is available, the more costs and more risks are associated with it,” Dr. Hall continues. “The devices are designed to promote myocardial and end-organ recovery, but outcomes have not changed in trials so far. Hospitals must make logical decisions about their resources and master the support devices that are available. It is also critical to have processes in place for deciding when to use them. Not every patient can be saved, so it’s also crucial to understand and recognize futility and not put a patient on a device when it’s too late.”
Pathway for instituting a shock program
Ultimately, only two interventions to date have demonstrated improvement in shock survival: utilization of Swan-Ganz catheter data to guide therapy and organized institutional protocols to recognize, evaluate and treat cardiogenic shock. To that end, Dr. Hall and her team have spent the last several years developing a formal shock protocol for the Baylor Scott & White Health system. Activated in June 2021 starting at Tier 1 centers, the protocol and processes will be fine-tuned over the next several months.
“Developing a shock team is a huge undertaking,” Dr. Hall says. “It takes a lot of discussion and clear agreement among all the stakeholders about what you’re going to do and how you’re going to do it. But a multidisciplinary cardiogenic shock team has been demonstrated to be much more effective in addressing all of the many different issues that surround a shock patient and improve survival. Eventually, all of the processes we’ve developed will span the entire health care system for the betterment of our patients.”