CE Article: Aortic Dissections and Aneurysms

Michael and Amy are completing their equipment check to start their shift when their alert tones go off. “EMS 22, respond to 2244 South Main, 63-year-old male with chest pain. This is a delta response. Time en route, 0712.”

After an uneventful response, the two paramedics arrive at a well-kept home. As they enter they are directed to the kitchen, where they find their patient, Henry, leaning in a tripod position. With clear shortness of breath, Henry says he has a tearing pain in the center of his chest that radiates into his left arm as well as his jaw. He is pale and diaphoretic.

Recognizing that Henry appears to be critically ill, Michael and Amy work together to quickly place him on oxygen and obtain vital signs, along with a 12-lead EKG. Henry’s 12-lead is normal, and Michael tells Amy that his vitals are pulse 118, respirations 24, and blood pressure 94/52. While Amy establishes an IV, Michael prepares the stretcher. Before they can assist Henry to the stretcher, though, he collapses forward and experiences a cardiac arrest.

When responding to complaints of chest pain, it is important to remember that your patient could be experiencing any one of more than 40 different diagnoses associated with that symptom. This month’s CE article reviews two of the most critical chest pain differential diagnoses: aortic dissection and aortic aneurysm.

Incidence

Neither dissections nor aneurysms are common. However, they are not rare, and the consequences of a missed diagnosis can be fatal. Aortic dissection is a catastrophic event with around 10,000 annual cases in the United States.1 While dissections can occur anywhere in the aorta, they occur in the thorax at a rate of 3:1 over the abdomen.1 EMS providers likely see more dissections than we realize, as dissections are identified as a primary cause of death in roughly 3% of all autopsies for unexpected death.2

Compared to dissections, aortic aneurysms are relatively common vascular emergencies occurring in the abdomen. When an aortic aneurysm ruptures prior to or during prehospital care, mortality exceeds 65% and increases by 1% for each minute that passes following rupture. Fortunately, when patients can reach a vascular surgeon prior to rupture, mortality drops to 5%.3 Nearly 75% of aneurysms occur in men, with the most frequent occurrences in males over age 50 who also smoke.2 Additional risk factors are listed in Table 1. Overall, fatal aneurysms occur in 15,000 Americans a year and are the 13th-leading cause of death in the United States.3 It is imperative that prehospital providers remain diligent in monitoring for aneurysms, as 80% of patients with a serious aneurysm present without a history of aneurysms.3

Anatomy Pathology

Exploring the physiology of aortic dissections and aneurysms requires a thorough understanding of the aorta. Originating from the left ventricle at the aortic valve, the aorta is the largest artery in the human body. It departs the left ventricle traveling superiorly towards the left clavicle before curving laterally and forming the aortic arch. As the aortic arch curves posteriorly and then medially, it brings the aorta back in line with the spine, where it then travels inferiorly.

Think of the aorta has having two regions: thoracic and abdominal. Within the thoracic region are the ascending arch and descending aorta. When the aorta passes through the diaphragm around the 12th thoracic vertebra, it transitions into the abdominal region. Here the aorta is further divided into the suprarenal and infrarenal segments, which are above and below the bifurcation of the renal arteries.

Upon leaving the left ventricle, the aorta is rather wide, at about 3 cm. The first arteries diverting blood from the aorta are the coronary arteries, followed quickly by the three great vessels off the arch: the brachiocephalic, left common carotid and left subclavian artery. As the aorta then travels inferiorly though the thorax, it reduces in size to about 2 cm by the time it reaches the abdominal region.

An impressive volume of blood under great force moves through the aorta as it travels from the heart until it divides into the iliac arteries just superior to the umbilicus. This protects and provides strength to the aorta. Like all arteries, the aorta has three distinct tissue layers: the tunica intima, media and adventitia. The innermost intima is composed of endothelial cells and is smooth compared to the muscular tunica media, which consists of elastin, collagen and proteoglycans; together these comprise the structural integrity of the artery. To provide the aorta with optimal strength, the medial layers are organized in spiral sheets of connective tissues. Finally the outermost tunica adventitia consists of collagen and minimal amounts of other cells, including the adrenergic nerves. These adrenergic nerves can sense pain, which is why the ripping associated with dissection is consistently felt.

As the aorta travels inferiorly, its volume of elastin and collagen decreases because less force is required to move blood as it travels farther from the heart. Elastin is the primary load-bearing structure of the aortic walls. Elastin, collagen and smooth muscles are arranged together in concentric layers. This promotes tolerance of high arterial pressures, but these structures are often found to be fragmented and weakened upon autopsy of patients with aneurysms.3

Physiology of Aortic Disease

Through the human aging process, there is a natural and gradual narrowing of the aorta caused by atherosclerosis. By age 50 the abdominal aorta narrows to 1.7 cm in men and 1.5 cm in women.3 While this narrowing may seem minimal, it can have profound changes on overall blood volume. Further, both elastin and collagen degrade with age and become weakened. These natural aging processes are exacerbated by chronic medical conditions such as hypertension, which is present in the history of 70% of patients who experience aortic dissections. Additional medical conditions that contribute to an increased risk of aneurysms and dissection are listed in Table 2.

Evolution of an aortic aneurysm

Aortic aneurysms exist when the aorta’s diameter increases by at least 50%. Dilation occurs as a result of the degradation of all three vessel layers, although it is most pronounced in the tunica media, where elastin and collagen fail.3

Dilation in the weakened aortic wall results in a ballooning-type effect. This ballooning can be on one side of the aorta or circumferential as shown in Figure 1. Whether circumferential or one-sided, the size of the aneurysm and its rate of change both predict the need for intervention, while the rate of size change is the greatest risk factor for rupture. Small aneurysms are less than 4 cm in diameter and have minimal risk for rupture. Table 3 shows the increase in rupture risk as aneurysm size increases. Figure 1 also demonstrates how aneurysms can occur in both the abdomen and thorax. Note the size and location; when the aneurysm develops near a major artery coming off the aorta, the distal organ may experience ischemia. For example, if the aneurysm develops around the renal artery, we can experience renal ischemia and prerenal failure.

An aneurysm in and of itself is not an emergency. Many people walk around with small and unrecognized aneurysms for years. However, as aneurysms increase in size, there is an increased risk for rupture. Often the aneurysm is first identified when the patient presents with a complaint such as flank pain and assumes they have a kidney stone. When a rupture occurs, a hole develops in the aortic wall, allowing blood to enter into the abdominal cavity and leading to a rapid onset of the most common presenting symptom: syncope. Since blood will flow from an area of high pressure to an area of low pressure, the blood will quickly flow from the high-pressure aorta into the low-pressure abdominal region. That’s why, when rupture occurs outside the hospital, mortality exceeds 65%.

Evolution of an aortic dissection

Aortic dissections occur when the connective tissue between the arterial layers fails and the two layers separate.2 Most often dissections are triggered by a tear in the tunica intima and high-pressure blood penetrating the potential space between the tunica intima and tunica media. As the blood penetrates this space, there is a horizontal or diagonal splitting of the two aortic layers, and a false lumen is created. In many instances this false lumen ends up being larger than the aorta’s true lumen. However, since no blood flows out of this false lumen, blood within it can become stagnant and clot, creating risk of embolism.

Over 90% of aortic dissections occur within the aortic arch beginning either 2 cm superior to the aortic valve or just distal to the left subclavian artery.2 Dissections here can impair blood flow to the left carotid artery and left arm as well as the right. Thus, one common symptom of aortic dissection is a difference of more than 20 mmHg between the right and left arm blood pressures; more than a third of patients with dissection present with this pulse differential.4 Additionally, until CT scan proves otherwise, aortic dissection needs to be your leading differential diagnosis in any patient complaining of a rapid onset of severe chest pain that leads to altered mental status.4

The location of an aortic dissection determines its classification. While there are two accepted classification systems, DeBakey and Stanford, the classification system is nowhere near as important as location identification. Figure 2 shows both classification systems; notice the DeBakey I and II are both Stanford A while DeBakey III is a Stanford B. DeBakey I dissections are the most serious and carry the greatest mortality. It is not uncommon for a DeBakey I dissection to also dissect into the right coronary artery and also cause STEMI on a 12-lead EKG. This patient requires emergency thoracic surgery over catheterization, though, and diagnosis is made based on clinical presentation.

Iatrogenic dissections can occur as a result of invasive medical procedures. During a cardiac catheterization, for example, puncture of the femoral artery can create the potential for the artery to dissect. While prehospital providers are unlikely to cause a dissection by puncturing an artery, they may perform interfacility transports of such patients.

Finally, dissections are considered acute when known to have existed for less than 14 days; once present for more than 14 days, they are chronic and have a lower mortality.2 Chronic dissections are often managed medically.

Case #1: Thoracic Aortic Dissection

You find your patient curled up in a ball on his bed, holding his chest and complaining of 10-out-of-10 midsternal tearing pains. While your partner obtains vital signs and a 12-lead EKG, you obtain a quick SAMPLE history:

S/Sx—In addition to pain, you observe your patient is anxious, and he says he felt like he was going to pass out when he tried to stand for the bathroom. His pain is described as:

     O—2:30 a.m.;

     P—No comfortable position;

     Q—Described as tearing, with numbness in the left arm;

     R—Described as spreading into the jaw and abdomen;

     S—10/10;

     T—Worsening for the past 30 minutes.

A—NKDA;

M—Metoprolol, nicotine patch, Lipitor and ASA;

P—Hypertension, 40-pack/year smoker, high cholesterol, coronary artery disease;

L—Dinner at 7:30 was a stir-fry;

E—Patient was asleep when the pain woke him.

As you finish, your partner reports that the 12-lead EKG shows sinus tachycardia without ST segment changes consistent with injury or ischemia, with a pulse of 108, regular and weak; respirations 24 and shallow; and a blood pressure of 172/118 in the right arm and 198/128 in the left. His skin is pale, cool and clammy.

You package your patient onto your stretcher and place him on oxygen via a nonrebreather mask. You elect to transport 25 minutes to the closest surgical trauma center over the community hospital ED 10 minutes away. During the transport you administer fentanyl for pain and an antiemetic, and apply an inch of nitro paste. After establishing a second IV site, you radio your report to the emergency department.

Based on your report the emergency department has the trauma room prepared for your arrival and urgently obtains a chest x-ray, which reveals a widened mediastinum consistent with an aortic dissection.

This patient showed the classic symptoms of aortic dissection, which include sudden and severe tearing chest pain. It is not uncommon for patients to describe their pain as radiating into the neck and jaw and arms in DeBakey I and II dissections and into the abdomen in DeBakey III dissections. Do not, however, attempt to diagnose a dissection type based on how pain radiates. Nearly 20% of patients present with neurologic symptoms including anxiety, syncope, altered mental status and even stroke symptoms.2

Exam findings during dissection are usually nonspecific, and dissections are best identified by having a high clinical suspicion. Always perform a 12-lead EKG to rule out STEMI. In some DeBakey I dissections, blood flow to the coronary arteries can be significantly reduced or cut off, causing a myocardial infarction. Fortunately this is rare, as it’s often a grave finding. Make it a standard practice to obtain bilateral blood pressures in all chest pain patients. An interarm systolic blood pressure difference greater than 20 mmHg is indicative, although not diagnostic, of dissection. Other prior vascular surgeries and injuries could also cause such a discrepancy.2

Hypertension during suspected dissection is a serious finding and requires intervention (described later), as it represents potential rupturing, cardiac tamponade and excessive vagal tone.2

Case #2: AAA

You and your partner have been requested to complete an emergent interfacility transport from an urgent care to the emergency department for an abdominal aortic aneurysm. Upon arrival you are directed by the receptionist to the patient area. A 65-year-old female lies on the stretcher in no apparent distress. She reports that she came in after “passing out” this morning at home, and all she knows is that the doctor examined her and then left quickly.

When the physician returns, he explains to you and the patient that she has a large pulsatile mass midline in her upper abdomen and several risk factors for an aneurysm, including multiple pregnancies, a history of hypertension and smoking.

As you assist your patient onto your stretcher, your partner begins to perform a physical exam. You establish baseline vitals: Her pulse is 84, strong and regular; blood pressure is 156/102; respirations are 18 with good tidal volume; and skin is pink, warm and dry. After completing his physical, your partner advises that there is no JVD, her lungs are clear, heart tones normal, and he too can feel the pulsating mass in her abdomen. She has equal and strong motor strength in all extremities and no neurological weaknesses. Your transport to the emergency department is uneventful. A 12-lead EKG is normal; you apply oxygen at 2 lpm via nasal cannula and establish an IV in each forearm.

The next day you go to see your medical director, concerned about being dispatched emergently for an asymptomatic patient and because you’re concerned that your partner palpated the abdomen of a known aneurysm. He explains that the partner part is easy: There is no clinical evidence that palpating the abdomen of a patient with an aneurysm will increase the likelihood of rupture.3 He explains that it is good medicine to complete your own physical exam to confirm the findings of others; he would do the same thing. He warns you, though, that a pulsatile mass is found in less than half of all nonruptured aneurysms, so its absence cannot rule out the diagnosis.

He continues that this patient had a classic presentation of an abdominal aortic aneurysm prior to rupture. Patients often remain asymptomatic while the aneurysm dilates unless there is sudden and rapid dilation, in which case you may observe that the patient has back and flank pain that radiates into the groin. Groin pain suggests retroperitoneal expansion and compression of the femoral nerve. Finally, nausea and vomiting are common associated findings. Should a rupture occur and bleeding into the abdominal cavity begin, anticipate the rapid progression of hemorrhagic shock that does not respond to aggressive fluid resuscitation. You will also observe the rapid development of cyanosis and mottling while cardiovascular collapse occurs.3

Treatment and Definitive Care

When treating a patient with a suspected dissection or aneurysm, management is based on the patient’s hemodynamic status. All patients require routine ALS interventions, including telemetry and a 12-lead EKG, oxygen via nasal cannula, and bilateral large-bore IV access, preferably 18-gauge or larger. Fluid resuscitation is not indicated unless rupture occurs and shock develops. Patients with an adequate blood pressure should receive a prophylactic antiemetic and an appropriate analgesic based on local protocols.

One of the most important steps prehospital providers can perform is the acquisition of a complete medicine list. The presence of any anticoagulation medicines will change patient care and require intervention. You may be the only one with the opportunity to identify these medicines. Finally, transport any suspected dissection or aneurysm to a facility with cardiothoracic capabilities, as the later need for interfacility transport of these patients can increase mortality through delays to definitive care.3

Critical care and interfacility teams that transport patients with dissections and aneurysms confirmed with a CT scan can provide more specific care to help prevent rupture. Prior to rupture, aggressive heart rate and blood pressure control is indicated.7 Most treatment protocols include a target systolic blood pressure of 100–120 mmHg and a target heart rate of 60–80 beats per minute.7

Frequently heart rate and blood pressure are controlled by administering an ultrashort-acting beta blocker such as esmolol. Esmolol is beta 1-selective and administered as a continuous IV infusion. Its effects stop within 1–3 minutes of the infusion being stopped, which is ideal in the event of rupture. Because of its beta 1-selective properties, it provides great heart rate control. Labetalol may be considered when esmolol isn’t available. Should hypertension continue after esmolol brings the heart rate into target range, you may consider an arterial vasodilator such as sodium nitroprusside or Cardene to reduce systolic blood pressure. Ensure your beta blocker is always given prior to considering administration of a vasodilator.

Critical care transport programs should place or request an arterial line whenever feasible. Ensure Foley catheter placement to monitor urine output. Less than half a milliliter of urine per kilogram of body weight per hour may indicate decreased renal perfusion and the involvement of a renal artery.

If rupture of either a dissection or aneurysm occurs, all medication infusions are discontinued and aggressive shock management is indicated. Ensure the patient is on high-flow oxygen via nonrebreather mask and anticipate the need for advanced airway management. Administer a minimum of 20 ml/kg of an isotonic fluid to maintain a target systolic blood pressure of 90 mmHg. Blood is indicated when permitted by local protocols. Pneumatic antishock trousers, though still used in some regions, can be detrimental to these patients and should be avoided.

Ultimately aortic aneurysms require surgical repair. Larger aneurysms may be repaired prior to rupture as an elective procedure. Emergency surgery is frequently required for DeBakey I and II dissections as well as complicated DeBakey IIIs. Some simple DeBakey III dissections may be managed medically, depending on factors such as the patient’s age and ability to recover following surgery. The location and size of an aortic emergency will drive the physician’s decision to perform an endovascular repair via a graft inserted through the femoral artery or perform open abdominal or thoracic surgery. The best prehospital providers can do is get these patients to a physician as rapidly as safely feasible, so they have time to make this decision.

Conclusion of Opening Case

Michael and Amy immediately request additional support and begin resuscitating their patient on scene with high-quality pit-crew CPR. Once an additional crew arrives, they place an advanced airway to support continuous chest compressions. Despite the administration of 6 liters of normal saline and proper ACLS medicines, the patient deteriorates from PEA into asystole. After 45 minutes of efforts, the resuscitation is terminated in the field.

In the paramedics’ system, a formal case review is completed with any crew-witnessed arrest terminated in the field. Since an autopsy was performed, Michael’s and Amy’s medical director could obtain the report prior to the review. He found they did everything properly and that the patient had an aortic dissection that began at the right subclavian artery and extended to the diaphragm. When it ruptured there was nothing they could have done. He congratulated them for a great effort.

Summary

Aortic dissections and aneurysms are seen with low frequency and have high risk for deterioration during prehospital care. It is essential to include both dissections and aneurysms in your differential diagnoses whenever evaluating patients with chest or abdominal complaints. Often a good history is the best indication of one of these grave vascular emergencies. Consider thoracic aortic dissection in your differential diagnosis for any patient who complains of chest pain and aortic aneurysm in patients who have any sort of abdominal discomfort or syncope with an unknown etiology. When either is suspected transport rapidly to a facility with cardiothoracic and vascular surgery capability, and provide care that prepares you to manage the patient quickly should a rupture occur.

References

1. Braverman AC. Aortic dissection: Prompt diagnosis and emergency treatment are critical. Cleveland Clinic J Med, 2011 Oct; 78(10): 685–96, www.ccjm.org/content/78/10/685.full.

2. Mancini MC. Aortic Dissection. Medscape, https://emedicine.medscape.com/article/2062452-overview.

3. Pearce WH. Abdominal Aortic Aneurysm. Medscape, https://emedicine.medscape.com/article/1979501-overview.

4. Klompas M. Does this patient have an acute thoracic aortic dissection? JAMA, 2002 May 1; 287(17): 2,262–72.

5. Inna P. Marfan syndrome. Medscape, https://emedicine.medscape.com/article/1258926-overview.

6. Mimoun L, Detaint D, Hamroun D. Dissection in Marfan syndrome: the importance of the descending aorta. Eur Heart J, 2011 Feb; 32(4): 443–9.

7. Wiesenfarth J. Acute Aortic Dissection. Medscape, https://emedicine.medscape.com/article/756835-overview#a1.

Kevin T. Collopy, BA, FP-C, CCEMT-P, NREMT-P, WEMT, is performance improvement coordinator for Vitalink/Airlink in Wilmington, NC, and a lead instructor for Wilderness Medical Associates. E-mail kcollopy@colgatealumni.org.

Sean M. Kivlehan, MD, MPH, NREMT-P, is an emergency medicine resident at the University of California, San Francisco. E-mail sean.kivlehan@gmail.com.

Scott R. Snyder, BS, NREMT-P, is a faculty member at the Public Safety Training Center in the Emergency Care Program at Santa Rosa Junior College, CA. E-mail scottrsnyder@me.com.