Class IV antidysrhythmics or calcium channel blockers have what action on the cardiovascular system?
Increase blood vessel spasm.
Decrease flow of calcium ions thus decreasing heart rate and contractions.
Decrease refractory period.
Increase heart rate.
The Correct Answer is B
Class IV antidysrhythmics or calcium channel blockers decrease the flow of calcium ions into cardiac and vascular smooth muscle cells, thus decreasing heart rate and contractions. By reducing the calcium influx, they also decrease the slope of phase 0 and 4 and prolong phase 2 of the cardiac action potential. This results in vasodilation, reduced myocardial oxygen demand, and decreased conduction through the AV node.
Choice A is wrong because calcium channel blockers do not increase blood vessel spasm, but rather cause vasodilation.
Choice C is wrong because calcium channel blockers do not decrease refractory period, but rather prolong it by extending phase 2 of the cardiac action potential.
Choice D is wrong because calcium channel blockers do not increase heart rate, but rather decrease it by slowing down the pacemaker activity and AV nodal conduction.
Normal ranges for heart rate are 60 to 100 beats per minute, and for blood pressure are 120/80 mmHg or lower.
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Related Questions
Correct Answer is D
Explanation
Choice A is wrong because calcium channel blockers (CCBs) are a class of drugs that prevent calcium from entering the cells of the heart and blood vessels, causing them to relax and lower blood pressure.
Examples of CCBs include amlodipine, diltiazem, verapamil, and nifedipine.CCBs are used to treat hypertension, angina, and arrhythmias.
Choice B is wrong because beta blockers are a class of drugs that reduce the heart rate and force of contraction, lowering the cardiac output and blood pressure.
Examples of beta blockers include atenolol, metoprolol, propranolol, and bisoprolol.Beta blockers are used to treat hypertension, angina, heart failure, and arrhythmias.
Choice C is wrong because platelet inhibitors are a class of drugs that prevent platelets from clumping together and forming blood clots.
Examples of platelet inhibitors include aspirin, clopidogrel, ticagrelor, and prasugrel.Platelet inhibitors are used to prevent or treat cardiovascular events such as heart attack or stroke.
Choice E is wrong because ACE inhibitors are a class of drugs that inhibit the enzyme that converts angiotensin I to angiotensin II, reducing the production of this vasoconstrictor hormone.
Correct Answer is A
Explanation
This is because low potassium levels (hypokalemia) increase the sensitivity of the heart to digoxin and can lead to toxicity even with normal serum digoxin levels. Digoxin inhibits the sodium-potassium pump on the cardiac cells, which causes potassium to accumulate outside the cells.Low potassium levels in the blood create a larger gradient for potassium to move out of the cells, which enhances the effect of digoxin and can cause arrhythmias.
Choice B is wrong because calcium 9.2 mg/dL is within the normal range (8.5 to 10.2 mg/dL) and does not increase the risk of digoxin toxicity.However, high calcium levels (hypercalcemia) can potentiate the effects of digoxin and cause toxicity.
Choice C is wrong because sodium 140 mEq/L is within the normal range (135 to 145 mEq/L) and does not increase the risk of digoxin toxicity.However, high sodium levels (hypernatremia) can reduce the binding of digoxin to the sodium-potassium pump and decrease its efficacy.
Choice D is wrong because magnesium 2.2 mg/dL is within the normal range (1.7 to 2.4 mg/dL) and does not increase the risk of digoxin toxicity.However, low magnesium levels (hypomagnesemia) can increase the sensitivity of the heart to digoxin and cause toxicity.
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