What's up family! I hope you and your loved ones are all doing wonderful this beautiful morning. Thanks for joining us for another Topic Tuesday! Today, I want to discuss a wonder drug called beta-blockers. These are one of the most commonly prescribed medications in America and for good reason - when appropriately taken, they help protect long-term heart function and prevent cardiovascular disease progression.
Let's start by talking first by what "beta" receptors usually do. The two main classes of beta receptors in the body are Beta 1 and Beta 2.
Beta-1 receptors work mainly in the heart and kidneys.
In the heart, activation of beta-1 receptors causes increased heart rate and heart contractility, essentially meaning your heart is beating strong and fast. As you can imagine, this puts a lot of stress on your heart as it works to keep up this pace.
In the kidneys, Beta 1 receptors activate the Renin-Angiotensin II-Aldosterone cascade. This is a long step-wise metabolic pathway that eventually results in absorption of salt and water in your urine, causing increased BP.
Beta 2 receptors work predominantly in the blood vessels, lungs and heart.
In the blood vessels, activation of beta-2 receptors causes smooth muscle relaxation and decreased blood pressure.
In the heart, activation of beta-2 receptors causes increased heart contractility.
In the lungs, activation of beta-2 receptors causes bronchiole relaxation allowing air to flow smoothly through the lung.
** Fun fact, the popular asthma drug "albuterol" inhalers, work by activating b2 receptors in the lung to improve breathing.
Beta blockers come in one of two main classes > nonselective beta-blockers work to block both beta-1 and beta-2 receptors, basically canceling out their downstream effects. While this may be useful in some regards, such as lowering blood pressure by reducing cardiac pumping and salt/water reabsorption in the kidneys (due to beta-1 blockade), it may have some unintended consequences such as bronchospasm and difficulty breathing (due to the beta-2 blockade).
Alternatively, some people may be more familiar with the "cardioselective" beta-blockers, such as the famous lopressor or "metoprolol." These drugs function to block ONLY the beta-1 receptors in the heart allowing them to reduce strain on the cardiac and aortic muscle while avoiding any unnecessary side effects from beta-2 blocking. The following table summarizes some common beta-blockers in each class - https://my.clevelandclinic.org/health/treatments/22318-beta-blockers
For patients with acute aortic dissection, cardioselective beta blockers are used to quickly decrease the stress of the heart on the aorta. In the hospital, this may be done by administering short quick-acting doses of esmolol to inhibit b1 receptors and slow down your heart rate in anticipation for further imaging or surgery. Survivors of aortic dissections are usually placed on long-term oral beta-blocker therapy to reduce the amount of work the heart does to pump and help offload some of the shearing stresses on the aortic wall to reduce risk of repeat dissection.
Other conditions in which beta-blockers are very commonly used include in patients after a heart attack to reduce heart strain on weakened cardiac tissue and in patients with heart failure. In fact, beta-blockers are one of only 4 drug classes that have been shown to prolong life expectancy in patients with heart failure. Can you guess the other 3? Comment below!
Nonselective beta blockers have also shown utility in many non-cardiovascular conditions, including but not limited to hyperthyroidism, anxiety, and tremor conditions. For more information, check out the following links / videos!
And that's it for this week! Thank you for joining us friends and be sure to check in next time for another post! Until then, think positive. Think Happy. Think Family. And Think Aorta!
AA
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