Control of Blood Pressure
It is vital that patients with suspected or proven dissection should have their blood pressure actively monitored and, if necessary, controlled. Hypertension is the major problem since this increases the risk of propagation of the dissection. A lower systolic blood pressure reduces the shear stress on the aortic flap and reduces the risk of further damage. However, hypotension could increase risk of organ compromise.
In theory, we would like the systolic blood pressure to be the lowest it can be, whilst still maintaining adequate end organ perfusion. In clinical practice, a cut off target for systolic blood pressure of <120 mmHg is generally used.
Similarly, heart rate control is also important since a higher heart rate increases the frequency of maximum stress exerted on the dissection. In practice, the target HR should be at least <80 bpm, though some publications advocate the more restrictive target of around 60 bpm.
During monitoring of BP, it is important to bear in mind that in type A dissection, blood pressures in each arm may be unequal. Both arms should be monitored, at least intermittently, and therapy should be targeted at the higher reading obtained. An arterial line must be placed to facilitate accurate measurement and control of BP.
Remember that the first step to controlling BP is often to provide adequate pain control, thereby reducing sympathetic stimulus. Opiate analgesia is normally indicated.
An intravenous β-blocker is generally the optimal first line anti-hypertensive. Historically, labetalol was considered the ideal agent to be used in this setting [5]. Labetalol’s advantage is that it has mixed alpha and beta blockade activity, but it is disadvantaged by its relatively long half-life of around 3-5 hours. This could cause difficulties if bleeding occurs, or there is haemodynamic instability. Where labetolol is used, it should be given as an initial bolus and then as an infusion with invasive arterial monitoring used to guide the actual dose.
More recently, esmolol has been considered the treatment of choice due to its rapid onset and offset time, which is advantageous in the management of a potentially unstable patient. Esmolol is a cardio-selective β1 receptor antagonist. It has an onset of action within 60 seconds, reaches a steady state within 2 minutes, and has a 9-minute half-life with rapid renal clearance.
If there is a strong contra-indication to β-blockers, then non-dihydropyridine calcium channel blockers (e.g. diltiazem or verapamil) could be considered, though this is rarely justified. In all cases, it may be worth involving other specialist teams (e.g. intensivists) to assist with management of BP.
An important point to remember is that anti-hypertensives which predominantly work by reducing systemic vascular resistance (vasodilators) will likely cause a reflex increase in contractility of the left ventricle which will potentially worsen the dissection. This is why β-blockers are favoured in the first instance, to first lower the heart rate.
Once the HR is around 60 bpm, if the BP is still not adequately controlled then a second agent, typically a nitrate-based vasodilator, should be considered.