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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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Digoxin is a cardiac glycoside that increases the force of heart contractions (positive inotropy) and decreases the heart rate (negative chronotropy) by inhibiting the sodium-potassium ATPase pump in the cardiac cell membranes and affecting the autonomic tone.This helps to improve the symptoms of heart failure and to control the ventricular rate in atrial fibrillation.
Choice A is wrong because positive chronotropy means increasing the heart rate, which is the opposite of what digoxin does.
Choice B is wrong because negative inotropy means decreasing the force of heart contractions, which is also the opposite of what digoxin does.
Choice D is wrong because positive inotropy and positive chronotropy would both increase the workload of the heart, which is not desirable in heart failure or atrial fibrillation.
Normal ranges for digoxin are 0.5 to 2 ng/mL for heart failure and 0.8 to 2 ng/mL for atrial fibrillation.Digoxin has a narrow therapeutic window and can cause serious side effects if overdosed or underdosed.
Correct Answer is ["B"]
Explanation
This is a mnemonic to remember the common suffix of drugs that block the beta receptors in the heart and blood vessels, which can lower blood pressure, heart rate, and reduce chest pain. For example, metoprolol, atenolol, and propranolol are beta blockers.
Choice A is wrong because calcium channel blockers do not end in DIPINE.
Calcium channel blockers are drugs that block the entry of calcium into the cells of the heart and blood vessels, which can relax the blood vessels and lower blood pressure.
Some calcium channel blockers end in DIPINE, such as amlodipine and nifedipine, but not all of them.
For example, verapamil and diltiazem are also calcium channel blockers.
Choice C is wrong because ACE inhibitors do not end in ZoSIN.
ACE inhibitors are drugs that inhibit the enzyme angiotensin-converting enzyme (ACE), which can lower blood pressure and prevent heart failure.
ACE inhibitors usually end in PRIL, such as lisinopril, enalapril, and captopril.
Choice D is wrong because angiotensin II receptor blockers do not end in STATIN.
Angiotensin II receptor blockers are drugs that block the action of angiotensin II, a hormone that constricts blood vessels and raises blood pressure.
Angiotensin II receptor blockers usually end in SARTAN, such as losartan, valsartan, and irbesartan.
The normal range for blood pressure is less than 120/80 mmHg.
The normal range for heart rate is 60 to 100 beats per minute.
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