7.2fg Cardiovascular Medications (Vasodilators, Beta Blockers, and Calcium Channel Blockers)

Vasodilators

1. Nitroglycerin:

• A common vasodilator used to dilate coronary arteries.
• Derived from natural nitric oxide (NO), which is a vasodilator produced in the body.
• Purpose:
  • Increases blood flow to the myocardium.
  • Reduces peripheral resistance, lowering the heart’s workload.
  • Primarily used to dilate coronary arteries to improve blood flow to the heart muscle, such as in angina pectoris or during myocardial infarctions.
• Mechanism:
  • Mimics nitric oxide (a natural vasodilator) by causing relaxation of blood vessel smooth muscles.
  • Works by causing myosin dephosphorylation in smooth muscle, preventing contraction and promoting relaxation and vasodilation.
  • Myosin dephosphorylation prevents contraction, leading to vasodilation.
• Caution: Careful dosage is key as excessive vasodilation can cause hypotension. leading to dizziness, fatigue, faintness, and reflex tachycardia.

2. Veno-Dilators:

• Help reduce high preload, reducing the volume the heart must pump, easing the heart’s workload.

3. Other Vasodilators:

• Vasodilators reduce systemic resistance (afterload), allowing the left ventricle to eject blood more efficiently.
• Dilating clenched arteries reduces afterload, making it easier for the left ventricle to eject blood, thus increasing stroke volume and cardiac output.
• Vasodilators reduce preload which as mentioned earlier, reduces the volume the heart must pump, easing the heart’s workload.

Beta Blockers

1. Function:

• Block beta-1 adrenergic receptors in the heart, preventing epinephrine and norepinephrine from binding.
• Beta Blockers therefore block the sympathetic “fight or flight” signals, keeping the heart calmer and less strained.
• Used to decrease heart rate and contractility, reducing cardiac output and easing workload on a stressed heart.

2. Practical Use:

• Helps in heart conditions by stabilizing heart function and preventing strain on the myocardium.
• Useful in heart disease, hypertension, and to reduce cardiac workload.

Calcium Channel Blockers

1. Function:

• Calcium Channel Blockers inhibit calcium ion entry through calcium channels in heart and/or smooth muscle cells.
• Just as a reminder:
  • Calcium entry typically occurs during depolarization, and cytosolic calcium then quickly binds to troponin, shifting tropomyosin off myosin-binding sites on actin.
  • After this shift, actin and myosin bind to each other and power stroking occurs, shortening sarcomeres and causing muscular contraction.
• Calcium Channel Blockers therefore, prevent calcium binding to troponin, effectively preventing the shifting of tropomyosin and therefore stops myosin-actin binding and muscle contraction.
• Some Calcium Channel Blockers are specific to calcium channels in cardiomyocytes (cardiac tissue) and others are specific to calcium channels in the smooth muscle of blood vessel walls.
• Importantly, the calcium channel blocker drugs used do not affect calcium channels in skeletal muscle cells.
• Heart muscle: Slows down contraction frequency and force, reducing workload.
• Smooth muscle of arteries: Promotes vasodilation, useful in treating hypertension and preventing angina by opening coronary arteries.

2. Mechanism:

• Calcium Channel Blockers inhibit calcium influx into heart muscle and smooth muscle cells.
• Calcium-Troponin Interaction: Calcium blocking inhibits this interaction, preventing troponin from shifting tropomyosin and stopping myosin-actin binding. This halts muscular contraction in targeted areas.

3. Usage:

• Alleviates symptoms in conditions with high blood pressure.
• Patients may experience exercise intolerance due to reduced ability to increase heart rate.

Summary:

Cardiovascular medications, including vasodilators like nitroglycerin, beta-blockers, and calcium channel blockers, are tailored to reduce cardiac workload and manage symptoms by influencing blood vessel tone and heart function. Vasodilators like nitroglycerin improve blood flow, while beta-blockers and calcium channel blockers reduce cardiac workload.  Proper dosage and use of these medications, focusing on individual mechanisms and effects, ensures safety and effectiveness in treating heart diseases, and minimizes risk of inducing hypotension.