Risk Stratification:
Is My Aneurysm at Risk for Rupture?

(Click the image above to see a larger version and click here for the full article from Circulation)

The 'rules' regarding thoracic aneurysms have changed somewhat over recent years. Most heart specialists learned in their training that ‘thoracic aneurysms do not require treatment unless larger than 5.5 cm (or 5 cm for Marfan Syndrome patients)'.

Multiple research papers now show that this algorithm may not be appropriate for all patients, despite the fact that it does work for most. Particularly, a world-wide registry that tracks aortic dissection, called IRAD (International Registry of Acute Aortic Dissection) produced a paper entitled: “Aortic Diameter > 5.5 cm Is Not a Good Predictor of Aortic Dissection” in the journal Circulation in 2008.

They retrospectively analyzed approximately 600 patients who presented to ERs with acute aortic dissection. The investigators found that an astounding 60% of acute aortic dissections occurred in aneurysms that measured less than 5.5 cm at the time of diagnosis, 40 % in those that measured less than 5 cm, and approximately 25% at sizes less than 4.5 cm. It is worth mentioning that the majority of these patients likely had no idea that they had an aneurysm, and likely never received counseling that could have impacted the incidence of aneurysm rupture/dissection.

Even more concerning, is the fact that aortic aneurysms typically become acutely larger when aortic dissection occurs. Unfortunately, the IRAD investigators do not give us guidance on why thoracic aneurysms can and do rupture or dissect at these 'smaller' sizes, but it is important to recognize that they can and that we take them seriously in terms of risk stratification and counseling.

When performing risk assessments for patients with thoracic aneurysm, our personal estimation of risk involves the following, and in order of decreasing importance:

1. Symptoms consistent with acute aortic dissection or rupture. Typically includes central chest discomfort that may radiate, sometimes including the throat or the upper back, often of sudden onset and very severe. IRAD actually reported a myriad of different symptoms that were associated with acute aortic dissection and can be found in this table. In facilities that have rapid access to CT scanners, the diagnosis of aneurysm with or without dissection can be made with high accuracy. When symptoms are present in the setting of an intact ascending aneurysm (especially associated with high blood pressure measured in the ER), urgent surgery might be indicated. If symptoms are totally under control, cardiac catheterization and/or echocardiography may be indicated to make sure that important valvular or coronary disease is not present. If symptoms cannot be eliminated with medications, emergent surgery is indicated without any further testing.
    
2. Symptoms in patients diagnosed with thoracic aneurysm that are not quite as dramatic as those in acute aortic dissection, that recur from time to time (especially associated with straining) and are not explained by other conditions (coronary disease, esophageal disorders, musculo-skeletal trauma). In these patients, elective aneurysm surgery should be strongly considered. Until we know more about why ‘smaller’ (< 5.5 cm) aneurysms sometimes have complications, these symptoms could be a ‘heads-up’ that an adverse aortic event is about to occur. If symptoms occur with straining or high blood pressure episodes (i.e. at the doctors' office, during an ER evaluation or using a home blood pressure monitor), the incidence of a complication is potentially higher, and urgent evaluation for surgery may be indicated. Patients may not realize that by straining (lifting heavy objects, or any activity that requires breath-holding: i.e. difficult bowel movement in the setting of constipation) may result in dramatic increases in blood pressure. Emotional stress or anxiety can also sometimes lead to spikes in blood pressure. Higher blood pressure may stretch the aneurysm, leading to symptoms, and an indication for intervention. It is a challenging decision to recommend surgery in these situations, particularly in the setting of small or modest sized aneurysms.
    
3. Situations in which the ‘relative aortic size’ (click here for full article) exceeds published guidelines. It is more than intuitive that a 5 cm aneurysm should represent a different risk to a petite (short stature) lady, as compared with a NBA center, especially in the setting of a genetic syndrome associated with aggressive aneurysm behavior. It is appropriate to compare aneurysm dimensions to body dimensions in certain scenarios. A relative risk system that has been incorporated into current AHA/ACC guidelines relates to patients with connective tissue disorders (i.e. the Marfan Syndrome) or Bicuspid Aortic Valve (BAV). Though Marfan Syndrome is relatively rare (1/10,000 in the general population), BAV is quite common (1/50 in the general population), and is over-represented in the aneurysm population at large. These patients have a genetically-driven absence or reduction of certain proteins that are the building blocks of blood vessels. This leads to weaker and more friable than usual aortas, that typically degenerate into aneurysms, and when they do, they behave in a much more malignant fashion than usual, and intervention has been traditionally recommended at smaller sizes. More recently, studies from Johns Hopkins University and the Cleveland Clinic have shown that a relative risk sizing system is better at predicting aortic dissection or rupture in both Marfan Syndrome patients as well as patients with BAV. A mathematical ratio between cross sectional area of the aorta at its maximum dimension divided by the patient’s height in meters yields a value that is of particular importance. When the Cleveland Clinic Foundation retrospectively analyzed patients operated for acute aortic dissection that were diagnosed with BAV at the time of emergency surgery, they found that using 2 standard deviations around the mean, 95% of aortic dissections could have been avoided in these patients if pre-emptively operated at a ratio above 9.5 cm/m2. For example, a patient with BAV who is 5’ 8” and has an aortic root aneurysm with a maximum diameter of 4.7 cm has a cross sectional area to height ratio of 10 cm/m2, favoring elective aneurysm surgery to prevent rupture or dissection.
   
   It is intuitive that relative aortic size should also be relevant in non-BAV/Marfan patients, and though a risk system for these ‘general' aneurysm patients has been proposed based on data from Yale University, these findings have not yet been incorporated into the latest AHA/ACC guidelines. This risk system may still have some usefulness, especially in equivocal patients who are experiencing intermittent chest or back discomfort as described above. The investigators found that creating a ratio between maximum aortic diameter and body surface area was more accurate at predicting adverse aortic events than maximum aortic diameter alone. Specifically, an Aortic Size Index of 2.75 cm/m2 or greater conferred a yearly risk of 8% of the cumulative end point of rupture, dissection and confirmed aneurysm-related death. For example, a patient who is 5’ 3” and 120 lbs (body surface area of 1.56 m2) with a 4.4 cm ascending aortic aneurysm has an aortic size index of 2.82 cm/m2 (maximum aortic diameter divided by body surface area). Such a patient could be considered for surgery outside of the guidelines particularly in the setting of recurring chest/back symptoms with an otherwise negative work-up.
   
   

   CLICK HERE TO CALCULATE YOUR RELATIVE AORTIC SIZE

    
4. Significant family history of thoracic aneurysm, aortic dissection or rupture, or unexpected death of a relative (especially a first degree relative) particularly at a young age without a known or proven cause. Aneurysms tend to run in families, and familial aneurysm is recognized as a subcategory of aneurysm patients that rupture or dissect at smaller sizes. No specific relative risk size systems have been validated for this group, but intervention at smaller sizes has been recommended (‘between 4 and 5 cm', according to AHA/ACC guidelines). Unless a relative aortic size threshold is appropriate, we would offer asymptomatic patients with confirmed or strong suspicion of familial aneurysm surgery by the time the aneurysm reaches 5 cm. Hopefully, clinical research will show which, if any, relative risk systems are appropriate. According to the NIH-funded Gen-TAC Registry, which studies genetically triggered thoracic aortic conditions, in patients with familial type A aortic dissection, the average age at first surgery was 51 years old.
    
5. Significant aortic valve stenosis or insufficiency associated with an aneurysm. Since the aortic root and proximal ascending aorta are anatomically associated with the aortic valve, as the aneurysm grows, it may stretch apart the leaflets of the valve, causing ‘leaking’ of blood back into the ventricle during the ventricle’s relaxation phase. This may lead to symptoms of fatigue and shortness of breath with exertion, and in extreme causes, overt heart failure symptoms. If moderate or greater aortic insufficiency is present with symptoms, or even in the absence of symptoms but associated with diminishing heart contractile function (ejection fraction %) or a dilating ventricle, surgery could be indicated electively to treat both the valve and aneurysm (a Class I indication when operating for the valve with aneurysm size > 4.5 cm). Often, leaking aortic valves associated with aneurysm can be treated with aortic valve repair, as opposed to replacement.
    
6. Young patients with aortic root aneurysm who could be candidates for valve-sparing surgery (the 'David' Procedure): Dr. David's own recommendation is for surgery at a root size of 5 cm. Allowing root aneurysms to become much larger could preclude the ability to preserve the patient's aortic valve and necessitate replacement instead. Valve-sparing aortic root surgery is the favored treatment (Class I) for younger patients with root aneurysm according to current guidelines. It is important to note that absent of genetic risk factors, current AHA/ACC guidelines have not yet incorporated this 5 cm threshold, and still indicate root replacement at a size of 5.5 cm.
    
7. Lifestyle or Occupational Risk. Individuals with aneurysm who strain heavily during recreation (i.e. weight lifting) must refrain from such activities (Class IIa indication in the guidelines) or modify them in such a way to minimize strain, since this can cause impressive spikes in blood pressure and heart rate, even in those without hypertension. Similarly, patients with severe constipation or urinary obstruction must be treated, so that they avoid settings where they must Valsalva (closing the vocal chords at same time as bearing down). Patients who have an aneurysm and whose profession requires them to strain on the job (heavy lifting, manual labor) may be at substantial risk for aortic events. Ideally, a change in job-related responsibilities can be made. If the patient can only work in such a profession in order to support his or her family, in rare instances elective surgery could be considered, with an anticipated return to work of approximately 3 months.
    

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