III. AORTIC DISSECTION
2.MRI
MRI proved remarkably useful and safe even in unstable patients with dissection in a blinded study by Nienhaber et al. In centers where new generation magnets are available, MRI may be the primary procedure of choice. New approaches to breath-hold magnetic resonance angiography (MRA) allow rapid acquisition and produce markedly improved images.
3.New Generation CT
Spiral or helical CT scan significantly reduces scanning time, reduces respiration and motion artifact, and allows more images during peak levels of contrast enhancement. Newer scanners can image the entire aorta within seconds displaying three-dimensional images and appearing to have a sensitivity and specificity comparable to that of TEE and MRI.
All three investigative methods, TEE, MRI, and CT, possess potential pitfalls in the evaluation of dissection and are complimentary. Two imaging modalities may be necessary to correctly establish the diagnosis of this life-threatening condition.
C. Management
1.Urgent Medical Management
Urgent medical management of aneurysm must be insti¬tuted. This includes immediate reduction in blood pressure to 100–120 mmHg and elimination of pain. The force of left ventricular ejection (dP/dt), or ejection velocity, must also be reduced rapidly with the use of an intravenous beta-blocking drug such as esmolol, meto-prolol, or propranolol. These agents are necessary even when the blood pressure is in the low normal range of 90–120 mmHg. If the blood pressure is severely elevated, labetalol, a beta-blocker with vasodilator activity, provides better control of the pressure and reduces dP/dt.