From the Guidelines
Blood pressure (BP) differences between arms greater than 20 mmHg systolic or 10 mmHg diastolic should raise suspicion for aortic dissection, especially when accompanied by severe, tearing chest or back pain. This discrepancy occurs because the dissection flap can obstruct blood flow to one of the subclavian arteries, reducing pressure in the corresponding arm, as noted in the 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease 1. When evaluating a patient with suspected aortic dissection, BP should be measured in both arms, and the higher reading should be used for clinical decision-making. Key considerations include:
- Accurate systemic blood pressure measurement may be complicated by dissection-related occlusion of aortic branch arteries, resulting in erroneously low blood pressure readings in the affected limb 1.
- Hypotension and shock can result from cardiac tamponade, aortic hemorrhage, severe aortic insufficiency, myocardial ischemia or infarction, true lumen compression by distended false lumen, or an intra-abdominal catastrophe 1.
- Patients with hypotension on admission were found more likely to have neurologic complications; myocardial, mesenteric, or limb ischemia; and death 1. If aortic dissection is suspected, immediate action is required: stabilize the patient, control blood pressure (target systolic BP 100-120 mmHg) using IV beta-blockers, obtain immediate imaging (CT angiography is preferred), and consult vascular surgery or cardiothoracic surgery. It is crucial to remember that not all patients with aortic dissection will have an arm BP discrepancy, and the absence of this finding does not rule out the diagnosis if other clinical features are present.
From the Research
Significance of Blood Pressure Arm Discrepancy
The significance of blood pressure (BP) arm discrepancy in the diagnosis of aortic dissection is a topic of interest in medical research.
- BP arm discrepancy is characterized by a difference in blood pressure readings between the two arms, which can be an indicator of aortic dissection 2, 3, 4.
- A study published in the Journal of Nippon Medical School found that an inter-arm difference in blood pressure (IADBP) is characteristic of acute aortic dissection (AAD), and that the prevalence of IADBP was higher in patients with type A AAD than in those without AAD 2.
- Another study published in the Emergency Medicine Journal found that a systolic BP differential >20 mm Hg was significantly associated with AAD, but had poor diagnostic accuracy and potential variability in measurement 3.
- A study published in Archives of Internal Medicine found that a large interarm blood pressure difference can help identify patients with aortic dissection, but that the degree of normal interarm blood pressure variation has not been well defined 4.
Diagnostic Accuracy
- The diagnostic accuracy of BP arm discrepancy in detecting aortic dissection is a topic of debate.
- A study published in the Journal of Nippon Medical School found that IADBP was characterized by R<L with low R in type A AAD, but was not associated with type B AAD 2.
- Another study published in the Emergency Medicine Journal found that pulse deficit had better diagnostic accuracy than systolic BP differential >20 mm Hg in isolation or combined with systolic BP differential >20 mm Hg 3.
Blood Pressure Control
- Blood pressure control is an important factor in preventing acute exacerbations of aortic dissection.
- A study published in Blood Pressure Monitoring found that invasive arterial BP control was important in preventing acute exacerbations, and that the time to target BP was significantly longer in the exacerbation group 5.
- Another study published in Perfusion found that intensive BP control increased the incidence of acute kidney injury and raised the utilization of anti-hypertensive drugs, but did not reduce operative mortality and late mortality in type B aortic dissection patients undergoing surgical repair 6.