Cath Lab Digest - December 2007 - (Page 35) 35 Figure 1. Figure 2. Table 3. Commonly administered beta-blockers Propranolol Labetalol Normodyne Atenolol Esmolol Metroprolol Sotalol Inderal Trandate, Tenormin Brevibloc Toprol Betapace myocardial infarction (AMI) will receive beta-blocker agents early in their treatment. It allows the heart to have a reduced workload. When to use alpha agents We will most commonly use alpha-stimulating medications when there is poor blood pressure because of unwanted vasodilation of the vasculature. This can also be considered in hypotensive states where we do not wish to over-stimulate the heart with beta agents. The alpha agents provide marked constriction of the vasculature, effectively increasing blood pressure. Considerations prior to agent administration Some important considerations before administration would be to detect the presence of any form of AV block. We would not want to administer an agent that could lower the heart rate to a patient already susceptible to an abnormally low heart rate. We would also not want to administer it to someone who is in an already hypotensive or hypovolemic state. We would also not want to administer it to someone with active bronchospams or a history of uncontrolled COPD, for the risk of bronchoconstriction would be present, and possibly worsened by, betablocker administration. One of the problems with patients on large doses of beta-blockers is that when they encounter a medical condition that would require an increase in heart rate (i.e., hypoxia, hypovolemia, etc.) the body can have a delay in achieving this heart rate increase. This delay is because of the beta blockade that will keep their heart rate and stroke volume lower and keep the body’s response to those conditions in check. One last tip As your cardiologist is running off his list of medications to administer during a case, how do you know what medications are beta-blockers? Simple. Any medication ending in “-lol” is a beta-blocker. Some examples of commonly administered beta-blockers are listed in Table 3. As you care for your AMI, hypertensive and angina patients, you can now see why beta-blocker administration can be important to control both their heart rate and blood pressure. ■ body results in increased heart rate, force of contractions, bronchodilation and vasodilation. When beta-blockers are administered, the beta receptor sites are not very specific, and can not differentiate between an actual agent and a blocker agent. The blocker agent takes up the receptor sites, preventing the beta stimulation actions from occurring. From what we discussed before, we know that the administration of betablockers would PREVENT chronotropic effects, it would PREVENT inotropic effects, it would PREVENT bronchodilation and PREVENT vasodilation. Understanding that beta-blockers have slight effects on the lungs and the vasculature, we can see how it can affect heart rate and blood pressure. If the beta receptors are ‘blocked’ to prevent stimulation, then the heart rate will not increase, and will likely even slow down a little because of the lack of ‘accelerant’ stimulation. If we remember that: CARDIAC OUTPUT (blood pressure) = STROKE VOLUME x HEART RATE then by changing the inotropic (force of contraction > stroke volume) and chronotropic (heart rate) effects, we can also manage the blood pressure. Ultimately, to answer your question, the blood pressure is lowered because we controlled the chrontropic and inotropic effects of that stimulation. The blocking of these actions also decrease the excitability of the heart (automaticity), decrease the cardiac workload (preload and afterload), and decrease myocardial oxygen consumption. These are the main reasons that patients with an active acute Next month, we will answer a question about activated clotting time (ACT) checks in the cath lab. Email your question to: tginapp@rcisreview.com Understanding that beta-blockers have slight effects on the lungs and the vasculature, we can see how it can affect heart rate and blood pressure. “The only foolish question is one left unasked.” New Staff: Your suggested topics and questions are needed! (You are welcome to remain anonymous.) Email us at: tginapp@rcisreview.com
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