An Elderly Woman with Acute Onset Chest Pain

Type A acute aortic dissection (TA-AAD). Cardiac POCUS imaging in the parasternal long axis revealed the intima of the ascending aorta undulating in and out of the left ventricular outflow tract throughout the cardiac cycle, consistent with a TA-AAD.

Discussion

In this case, POCUS resulted in the early diagnosis and prompt treatment of TA-AAD. Cardiothoracic surgery was immediately consulted, and after correcting her supratherapeutic INR, she was taken to the OR for emergent surgery. She received a bioprosthetic aortic valve and her aortic root was replaced with a synthetic graft. Her left atrial appendage was excluded with a clip to lower her long-term risk of stroke in the setting of atrial fibrillation. She had an uneventful recovery and was discharged home in stable condition.

There are two commonly described mechanisms by which TA-AAD occur. A tear in the aortic intima allows high-pressure blood to enter the media and separates the two layers. Alternatively, a rupture of the vasa vasorum allows blood to enter the aortic media creating a hematoma that forces the two layers apart. The later is considered to be much less common, accounting for only 5-10% of reported cases¹.

In one large registry study, in-hospital mortality from TA-AAD was 34.9%. This study noted the highest mortality occurs in the first 7 days after the development of symptoms². Other investigators have determined that TA-AAD has a mortality rate of 1-2% per hour over the first 24 to 48 hours³. This pattern of early mortality after the development of symptoms emphasizes the importance of making a timely diagnosis of TA-AAD.

In general, transthoracic sonography is not considered to be a reliable diagnostic tool for TA-AAD. A retrospective single center study reported on 270 patients suspected of having either an ascending aortic dissection or intramural hematoma who were initially screened for disease using transthoracic echocardiography (TTE). The reported sensitivity, specificity, positive and negative predictive values for TTE in the diagnosis of TA-AAD were 87%, 91%, 75%, and 95% respectively. The 58 patients who were correctly diagnosed by TTE experienced a rapid transit time from admission to the operating room (43 ± 25 minutes)⁴. However, had TTE been the sole diagnostic modality, 9 cases of TA-AAD would have been missed and these patients would have likely died. It must be further noted that this study tested TTE using a full-sized ultrasound machine, and the exams were performed and interpreted by experienced cardiologists who utilized additional views which are not routinely executed by POCUS practitioners. Thus, it is likely the test performance characteristics of cardiac POCUS for diagnosing TA-AAD are even less robust.

Despite these shortcomings, cardiac POCUS can be performed quickly and does not require either transport or IV contrast. This case illustrates how intensivists performing routine cardiac POCUS exams need to be able to identify both direct and indirect signs consistent with TA-AAD or else an opportunity to provide expedited care may be missed. For example, it is important to recognize the presence of an intimal flap which must be differentiated from reverberation or mirror artifact originating from nearby structures. Color Doppler can aid in identifying both true and false lumens along with aortic regurgitation. Finally, depending on the clinical setting other findings may be associated with TA-AAD and should raise concern for this diagnosis including: bicuspid aortic valve, dilated aortic root, aortic regurgitation and pericardial effusion.

References

1. Mann DL, Zipes DP, Libby P, Bonow RO, Braunwald E. Braunwald's heart disease : a textbook of cardiovascular medicine. Tenth edition. ed. Philadelphia, PA: Elsevier/Saunders; 2015.
2. Fojtik JP, Costantino TG, Dean AJ. The diagnosis of aortic dissection by emergency medicine ultrasound. J Emerg Med. 2007;32(2):191-196.
3. Chirillo F, Marchiori MC, Andriolo L, et al. Outcome of 290 patients with aortic dissection. A 12-year multicentre experience. Eur Heart J. 1990;11(4):311-319.
4. Cecconi M, Chirillo F, Costantini C, et al. The role of transthoracic echocardiography in the diagnosis and management of acute type A aortic syndrome. Am Heart J. 2012;163(1):112-118.