February 2019, Volume XXXII, No 11

PROFESSIONAL UPDATE: Cardiology

Acute aortic dissection

Timely recognition and multidisciplinary care

n acute aortic dissection (AD) occurs when there is a tear in the intima, the inner layer of the aorta, allowing blood to travel through a separate channel (false lumen), often leading to complications which may include cardiac tamponade, aortic regurgitation, ischemia of the branch vessels, and, ultimately, aortic rupture. The patient’s symptoms depend on the path of the dissection and which organs are malperfused. Most commonly, patients with AD have symptoms of chest or back pain that may mirror the much more prevalent acute coronary syndromes, and are frequently mistreated as such. If the ascending aorta (Type A) is involved, this condition represents an acute surgical emergency, with a mortality that is historically 1 percent per hour until surgery can be performed. The Minneapolis Heart Institute (MHI) at Abbott Northwestern Hospital (ANW) has developed an AD Program with a goal of increasing recognition and more rapidly instituting treatment.

Clues to recognition

A focus of the American Heart Association guidelines for aortic disease is timely recognition of AD. On average, in the International Registry of Acute Aortic Dissection (IRAD), the median time for presentation to diagnosis of AD is 4.3 hours, with an additional 4.3 hours until surgical intervention. Given that delays may be even longer when patients are transferring from outlying hospitals, there is a need for a streamlined process to rapidly diagnose and transfer these critically ill patients. Unfortunately, delays in recognition do occur. In some cases the diagnosis is not established until autopsy, which illustrates how critical early recognition is.

Early recognition is best made by the clinician integrating high-risk historical features (known aortic aneurysm, aortic valve disease, family history of aortic disease, prior cardiac surgery), symptoms (severe, sudden chest/back pain), and exam findings (blood pressure discrepancy, pulse deficit, diastolic murmur suggestive of aortic regurgitation, or neurologic finding). The vast majority of patients with AD will have one of these clinical findings. Most ADs occur in males with a mean age of 62 years, though it can occur in patients across a wide age spectrum. Younger patients that have connective tissue disease may be afflicted, and although rare, females during or after pregnancy can be at risk. Overall incidence is approximately three per 100,000 people annually. Although more common in males, females typically present with AD at an older age, and often have more severe in-hospital complications and mortality.

Significant delays in recognition can occur in patients with atypical presentations, such as those without pain, in females, and among those presenting to non-tertiary hospitals. Clinical suspicion is confirmed via diagnostic testing, most commonly computed tomography (CT) imaging—though transesophageal echocardiography (TEE) or magnetic resonance imaging (MRI) could also be used.

Aortic dissection represents a high-risk surgical emergency.

Initial treatment

Once an AD is recognized, the principles of medical therapy include control of the patient’s blood pressure with beta blockade principally, but also with pain medications. At the time of transfer, the focus of the team is blood pressure and heart rate control preferentially with beta blockers. The goal of care during this early phase is to prevent the dissection from extending or rupturing by both lowering the pressure and by lowering the number of pulses being generated. This last point, limiting pulse generation, is one of the keys to using beta blockers over other anti-hypertensives.

If the patient presents to a non-tertiary hospital, it is imperative the patient move quickly to a facility with expertise in surgical treatment. If the ascending aorta is involved, (Type A AD), and the patient is a surgical candidate, then urgent surgery should occur. The corrective surgery includes graft replacement of the ascending aorta (often including the under surface of arch). With a Type B AD (where the tear starts in the descending aorta), consultation with a vascular surgeon is needed, and if high-risk features are present, such as ischemia of the mesenteric or peripheral vessels, then an urgent surgical procedure (often stent grafting) should take place.

Needs for improvement

Since AD is significantly less common than acute coronary syndromes, the clues suggesting the diagnosis are less evident and, without a point-of-care laboratory assay, the diagnosis is often delayed or missed. Death in AD is most frequently due to aortic rupture, and thus lifesaving surgery must be initiated before this occurs. The AD Program was created based on the same principles of the Level 1 Heart Attack program for ST elevation myocardial infarction, which emphasizes standardized and protocolized care in concert with a regional referral network resulting in rapid transport directly to the cath lab for emergent percutaneous coronary intervention.

Components of the AD Program

The multidisciplinary AD Program goals included standardizing diagnostic testing/imaging, decreasing the time to diagnosis and surgical treatment, early and aggressive blood pressure control, rapid access to blood products, and standardizing intraoperative imaging and surgical techniques.

Once the diagnosis of AD is confirmed, a call through a dedicated emergency phone number is used to arrange transfer to the AD team, including cardiothoracic and/or vascular surgeons, cardiologist, and emergency physician. Image transfer is also a priority. Throughout this phase in the AD protocol, order sets (which specify blood pressure goals, including recommended doses of beta blockers) are utilized by the transferring team to standardize care between providers and hospitals within the same system. This process focuses the team on clinical priorities and ensures critical steps are addressed during the final preparation for surgery. (For current AAD protocols, install the MHI/ANW CV Resources App, which includes information on cardiovascular protocols, as well as a checklist on Aortic Dissection (AoD) Protocol. This latter checklist is also available at www.tinyurl.com/mp-AD-Protocol).

While the patient is en route, a page goes out to assemble the surgical team, and to notify the emergency department (ED) and accepting units of impending arrival of an AD. With outside transfers, all surgical emergencies go through the ED, where the patient meets the emergency physician, cardiologist, and cardiovascular and/or vascular surgeon. This allows time for massive transfusion orders to be placed, the operating room (OR) to be prepped, and the opportunity for repeat imaging if needed. The OR staff, led by the anesthesiologist, moves the patient from the ED to the OR and rapidly prepares the patient for surgery. The use of TEE for intraoperative imaging is universal and helps confirm the anatomy of proximal aorta and additional cardiovascular findings. These TEE findings aid in surgical decision-making regarding concomitant need for aortic valve surgery. Over the past five years, vascular surgery has been actively involved in all Type A AD. Selected patients with high-risk features, including branch vessel ischemia or descending aorta progression, are managed with a hybrid approach where a concomitant stent graft is placed at the time of ascending/arch repair. Following surgery, hospitalized patients are cared for by a multidisciplinary team including the surgical teams, intensive care, and cardiology.

Patients with AD present with acute chest or back pain.

Follow-up

An additional key component of the AD Program is systematic surveillance, including standardized imaging and clinical follow-up. Clinic visits emphasize blood pressure management with guideline-directed pharmacotherapy; work and lifestyle advice, including tobacco cessation; genetic screening in specific cases; and coordinated familial screening. AD is a lifelong disease that requires regular follow-ups to decrease adverse outcomes. Patients are at continued risk of progressive aortic expansion, new dissection, and aortic rupture years after the initial event (see Figure 1).

Figure 1. CT sagittal view of a Stanford type B aortic dissection showing the true lumen separated from the false lumen by the intimal flap.

Patients undergo CT or MRI imaging prior to discharge, along with an echocardiogram, and tomographic imaging should be repeated at three, six, and 12 months, and then annually thereafter as suggested by American Heart Association’s aortic guidelines. Patients who are compliant with follow-up clinic visits and imaging have improved outcomes.

Successes

Data shows that both time to diagnoses and treatment of AD has improved with the implementation of the AD Program. Since the initiation of the protocol, the median time from outside hospital presentation to diagnosis decreased by 43 percent, and time to OR by 30 percent. For patients transferred from outlying hospitals, the overall time from arrival decreased by over six hours, a rather significant time in a condition that has a 1 percent/hour mortality. The 30-day mortality rate for surgical Type A’s has decreased and is at 14 percent for the last three years, while 30-day Type B mortality has decreased to 14 percent overall. Additional improvements include almost all eligible patients receiving beta blockers at time of arrival and discharge, and intraoperative TEE is now used in all surgical cases.

Conclusion

Aortic dissection represents a high-risk surgical emergency that requires immediate recognition and streamlined management. Patients with AD present with acute chest or back pain, and clues to recognition may include high-risk historical features (aortic valve or connective tissue disease, family history of aortic disease, prior cardiac surgery) or physical exam features including perfusion deficit, diastolic murmur, or hypotension.

The AD Program was the first of its kind to systematically treat these high-risk patients with a multidisciplinary care team in conjunction with regional partners. This approach has led to earlier recognition, decreased time to treatment, and guideline-directed blood pressure and heart rate management. Additionally, MHI surgeons have adopted a hybrid approach to Type A AD patients, allowing cardiothoracic and vascular surgeons to work simultaneously, address high-risk potential complications, and reduce the potential need for future surgeries. Following initial treatment of AD, patients remain at lifelong risk for complications and benefit from ongoing surveillance and guideline-driven management of risk factors to ensure longevity.

Jasmine Curry, BS, is a physiology graduate from the University of Arizona, and worked at the Minneapolis Heart Institute Foundation summer intern program on aortic dissection research in 2018. She is now enrolled in the Wy’east Post-Baccalaureate Program at Oregon Health and Science University, where she will attend medical school.

Matt Pavlovec, RN, BSN, is the clinical coordinator for the CV Emergencies Program at Minneapolis Heart Institute/Abbott Northwestern Hospital, which includes the Level 1 STEMI, ECPR, and Aortic Dissection Programs. He brings over 20 years of combined nursing and paramedic experience in cardiovascular, critical care, and emergency medicine.

Kevin M. Harris, MD, is a clinical cardiologist, echocardiographer, site director of cardiology training, and the aortic dissection program at the Minneapolis Heart Institute/Abbott Northwestern Hospital. He is a member of International Registry of Acute Aortic Dissection. 

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Kevin M. Harris, MD, is a clinical cardiologist, echocardiographer, site director of cardiology training, and the aortic dissection program at the Minneapolis Heart Institute/Abbott Northwestern Hospital. He is a member of International Registry of Acute Aortic Dissection.