Why do asymmetric blood pressures occur in aortic dissection?

From the Guidelines

Asymmetric blood pressures in aortic dissection occur due to the obstruction of blood flow to various arteries by the dissection flap, which can lead to a measurable difference in blood pressure between the two arms or between upper and lower extremities. This phenomenon is a result of the dissection extending into the aortic arch or branches, partially or completely blocking blood flow to one arm, and creating a false lumen that can compress the true lumen or directly obstruct branch vessels 1. The mechanism behind this is crucial in understanding the clinical significance of asymmetric blood pressures in aortic dissection, as it serves as an important diagnostic clue for this life-threatening condition.

When an aortic dissection occurs, the dissection flap can obstruct blood flow to various arteries, including those supplying the arms, resulting in a measurable difference in blood pressure between the two arms (typically >20 mmHg) 1. This finding is clinically significant as it warrants immediate imaging studies such as CT angiography to confirm the diagnosis. According to the 2024 ESC guidelines for the management of peripheral arterial and aortic diseases, early diagnosis and treatment of aortic dissection are crucial to reduce in-hospital mortality, which can reach 60% 1.

Key points to consider in the management of aortic dissection include:

• Initial reduction of the pulse pressure by lowering SBP below 120 mmHg and heart rhythm ≤60 beats per minute (b.p.m.) to decrease aortic wall stress and avoid further extension of dissection 1
• Use of intravenous beta blockade, such as labetalol, as the first choice for initial treatment, due to its alpha- and beta-blocking properties 1
• Consideration of higher BP tolerance in cases of malperfusion to optimize perfusion to the threatened region 1
• Early placement of an arterial line to monitor BP invasively and admission to an intensive care unit for close monitoring and management 1.

In patients presenting with chest or back pain, the presence of asymmetric pulses or blood pressures should always raise suspicion for aortic dissection, and immediate imaging studies should be performed to confirm the diagnosis 1.

From the Research

Asymmetric Blood Pressures in Aortic Dissection

• Asymmetric blood pressures in aortic dissection can be attributed to several factors, including the location and extent of the dissection, as well as the presence of any underlying medical conditions 2.
• The dissection can cause a separation of the aortic wall layers, leading to the creation of a pseudolumen that may compress the true aortic lumen, resulting in uneven blood pressure readings 2.
• Hypertension is a common predisposing factor for aortic dissection, and uncontrolled high blood pressure can exacerbate the condition, leading to further dissection and potential organ damage 2, 3.
• The management of aortic dissection involves controlling blood pressure, heart rate, and pain, with the goal of preventing further dissection and promoting healing 4, 3.
• The choice of intervention varies depending on the type of dissection, with surgical repair, endovascular repair, and medical management being considered as treatment options 2.

Hemodynamic Instability

• Hemodynamic instability, including hypotension and bradycardia, can occur in patients with aortic dissection, particularly during treatment with antihypertensive agents 5, 6.
• The use of esmolol and labetalol has been studied in the management of aortic dissection, with varying results in terms of achieving heart rate control and preventing hemodynamic instability 5, 6.
• The incidence of hemodynamic instability was found to be higher in patients receiving high-dose continuous intravenous labetalol compared to those receiving esmolol combination therapy, although the difference was not statistically significant 6.

Clinical Implications

• Prompt recognition and management of aortic dissection are crucial to prevent further dissection and promote healing 4, 3.
• Controlling blood pressure and heart rate is essential to prevent target organ damage and reduce the risk of mortality 4, 3.
• Further studies are needed to evaluate the optimal treatment strategies for aortic dissection, including the use of antihypertensive agents and the role of endovascular repair in uncomplicated type B dissections 5, 6, 2.