Ask the Clinical Instructor: A Q&A column for those new to the cath lab

Todd is the Cardiology Manager for Memorial Hermann Southeast in Houston, Texas. He also teaches an online RCIS Review course for Spokane Community College, in Spokane, Washington, and regularly presents with RCIS Review Courses. “I was involved in one of our initial carotid stent procedures, and during the ballooning, the patient went severely bradycardic and hypotensive. What happened?!” — Online RCIS Review participant I had to chuckle when I read your question, because many of us were in the same position the first time our facilities participated in such a procedure. I understand EXACTLY how you felt. As carotid artery stenting (CAS) is occurring more frequently, I think most people are now aware of this occurence. However, it is a good question to help people who haven’t yet experienced it. The reason this happens is because of the baroreceptors in our body. Let’s talk about this for a minute. What is a baroreceptor? According to Webster’s Dictionary, it is “a nerve ending sensitive to pressure: in the circulatory system, they help regulate the dilation of blood vessels by reacting to blood pressure.” That probably gives you an answer right there, but let’s define it further. Arterial baroreceptors are present in the aortic arch and the carotid sinuses of the left and right internal carotid arteries. The baroreceptors found within the aortic arch enable the body to assess the pressure of the blood being delivered to all the blood vessels via the systemic circuit, and the baroreceptors within the carotid arteries do the same with the blood pressure of the blood being delivered to the brain. These baroreceptors are stimulated by pressure changes in the arteries. The baroreceptors can identify the changes in the blood pressure which can increase or decrease the cardiac output. The receptors are actually nerve endings that lie in the wall of the artery. They are different from the “medication receptors” we have discussed in previous articles. Baroreceptors respond very quickly to alterations in the blood pressure, but they only respond to short-term changes. In long-term changes, for example, in people with chronic hypertension, the baroreceptors respond as if the elevated blood pressure is normal. Over the long term, the baroreceptors try to maintain this high blood pressure. In the cardiac cath lab, there are two receptors with which we are mainly concerned. The receptors in the aorta, and the receptors in the internal carotid arteries (ICA) (Figure 1). As we stated, these receptors keep an eye on the blood pressure status within the body, and respond accordingly when there is distress. When a patient suffers physical trauma (in a car accident, for example) and subsequent hypovolemia, the receptors in the aortic arch are able to identify a decrease in pressure because of the hypovolemia. This results in an initial tachycardia and peripheral vasculature constriction in an attempt to increase blood pressure and cardiac output. In coronary artery stenting (CAS), we initiate a reverse response. During angioplasty of either a bifurcating external carotid artery (ECA) and ICA, or just an ICA angioplasty, a balloon is generally inflated at some point during the procedure. When the balloon inflates, the walls of the artery are expanded slightly. The baroreceptors in the ICA ‘see’ this as an increase in pressure because of that artery expansion. They respond as if there was a condition of hypervolemia or acute hypertension, and try to reduce cardiac output. One of the quickest ways to reduce cardiac output is the reduction of the heart rate. Therefore, bradycardia often occurs immediately. When the heart rate slows down, the cardiac output also decreases, and hypotension is seen. This is not considered a ‘complication’ of the procedure. It is considered a normal hemodynamic response TO the procedure. It is seen approximately 40% of the time either at the point of the balloon inflation, or occasionally post procedure.1 It can be easily managed, dependant upon physician preference. This preference should be identified before the procedure even starts, so staff can be prepared with the right supplies and response. Management can include: 1. Since the balloon inflations are relatively short in duration, the hemodynamic adjustment can also be short in duration. Some physicians will do nothing but administer fluids aggressively and allow the body to return to its normal state. 2. Some physicians will treat the bradycardia with atropine 0.5mg IV and IV fluid bolus administration. 3. There are some studies that indicate a pre-cautionary dose of atropine, usually 0.5mg IV, prior to the inflation of a balloon device. However, in the elderly, routine administration of atropine is also associated with significant side effects, such as urinary retention, severe dry mouth and confusion.1 4. Pacing is rarely needed, but should be readily available.2 Some physicians may opt to have a temporary pacing catheter in place prior to the balloon/stenting procedure based upon previous history and clinical history of the patient. Once the ballooning and treatment measures are complete, hemodynamic status returns to normal relatively quickly. As with many other procedures, the procedural staff needs to be aware of what CAN happen and have that in their minds as the procedure progresses. Having the equipment available to manage these events is necessary. Next month, we’ll address a question about troponins. Email your question to: tginapp@rcisreview.com

1. King SB, Yeung A. Interventional Cardiology. New York: The McGraw-Hill Companies; 2007.
2. Baim DS, ed. Grossman’s Cardiac Catheterization, Angiography, and Intervention. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006.