CH.48
KEY POINTS
▪ Calcium channels are gated pores in the cytoplasmic membrane that regulate calcium entry into cells.
▪ In blood vessels, calcium entry causes vasoconstriction, and hence calcium channel blockade causes vasodilation.
▪ In the heart, calcium entry increases heart rate, AV conduction, and myocardial contractility, so calcium channel blockade has the opposite effects.
▪ In the heart, calcium channels are coupled to beta1-receptors, activation of which enhances calcium entry. As a result, calcium channel blockade and beta blockade have identical effects on cardiac function.
▪ At therapeutic doses, nifedipine and the other dihydropyridines act primarily on VSM; in contrast, verapamil and diltiazem act on VSM and on the heart.
▪ All CCBs promote vasodilation and hence are useful in hypertension and angina pectoris.
▪ Because they suppress AV conduction, verapamil and diltiazem are useful for treating cardiac dysrhythmias in addition to hypertension and angina pectoris.
▪ Because of their cardiosuppressant effects, verapamil and diltiazem can cause bradycardia, partial or complete AV block, and exacerbation of heart failure.
▪ Beta blockers intensify cardiosuppression caused by verapamil and diltiazem.
▪ Nifedipine and other dihydropyridines can cause reflex tachycardia. Tachycardia is most intense with IR formulations and much less intense with SR formulations.
▪ Beta blockers can be used to suppress reflex tachycardia caused by nifedipine and other dihydropyridines.
▪ Because they cause vasodilation, all CCBs can cause dizziness, headache, and peripheral edema.
▪ In toxic doses, nifedipine and other dihydropyridines can cause cardiosuppression, just like verapamil and diltiazem.
▪ IR nifedipine has been associated with increased mortality in patients with myocardial infarction and unstable angina, although a causal relationship has not been established. The National Heart, Lung, and Blood Institute recommends that IR nifedipine, especially in higher doses, be used with great caution, if at all.
Summary of Major Nursing Implicationsa
VERAPAMIL AND DILTIAZEM
Therapeutic Goal
Verapamil and diltiazem are indicated for hypertension, angina pectoris, and cardiac dysrhythmias (atrial fibrillation, atrial flutter, and paroxysmal supraventricular tachycardia).
Recognize Cues
For all patients, determine blood pressure and pulse rate and obtain laboratory evaluations of liver and kidney function.
For patients with angina pectoris, obtain baseline data on the frequency and severity of anginal attacks. For baseline data relevant to hypertension, see Chapter 50.
ANALYZE CUES AND PRIORITIZE HYPOTHESES
Identifying High-Risk Patients
Verapamil and diltiazem are contraindicated for patients with severe hypotension, sick sinus syndrome (in the absence of electronic pacing), and second-degree or third-degree AV block.
Use with caution in patients with heart failure or liver impairment and in patients taking digoxin or beta blockers.
Generate Solutions
Minimize Risks for Cardiosuppression
Inform patients about manifestations of cardiac effects (e.g., slow heartbeat, shortness of breath, weight gain) and instruct them to notify the prescriber if these occur.
The combination of digoxin with verapamil or diltiazem increases the risk of partial or complete AV block. Monitor for indications of impaired AV conduction (missed beats, slowed ventricular rate).
Verapamil (and possibly diltiazem) can increase plasma levels of digoxin. Digoxin dosage should be reduced.
Concurrent use of a beta blocker with verapamil or diltiazem can cause bradycardia, AV block, or heart failure. Monitor closely for cardiac suppression. Administer intravenous verapamil and beta blockers several hours apart.
Minimize Risks for Peripheral Edema
Inform patients about signs of edema (swelling in ankles or feet) and instruct them to notify the prescriber if these occur. If necessary, edema can be reduced with a diuretic.
Minimize Risks for Constipation
Constipation occurs primarily with verapamil.
Advise patients that constipation can be minimized by increasing dietary fluid and fiber.
Minimize Risks for Acute Toxicity
Grapefruit juice can raise levels of verapamil and diltiazem, although new evidence reveals this is less than originally thought. Nevertheless, toxicity may result. Advise patients that it may be prudent to minimize grapefruit juice consumption.
Take Actions
Routes
Oral, IV.
Administration
Oral
Extended-release formulations are reserved for essential hypertension. Instruct patients to swallow ER formulations whole, without crushing or chewing.
Intravenous
IV therapy with verapamil or diltiazem is reserved for cardiac dysrhythmias.
Perform injections slowly (over 2 to 3 minutes).
Monitor the electrocardiogram (ECG) for AV block, sudden reduction in heart rate, and prolongation of the PR or QT interval.
Have facilities for cardioversion and cardiac pacing immediately available.
Evaluate Outcomes
Angina Pectoris
Keep an ongoing record of anginal attacks, noting the time and intensity of each attack and the likely precipitating event.
Teach outpatients to chart the time, intensity, and circumstances of their attacks and to notify the prescriber if attacks increase.
Essential Hypertension
Monitor blood pressure periodically. For most patients, the goal is to reduce systolic/diastolic pressure to a value below 140/90 mm Hg.
Teach patients to self-monitor their blood pressure and to maintain a blood pressure record.
DIHYDROPYRIDINES
Therapeutic Goal
Amlodipine, nifedipine, and nicardipine are approved for essential hypertension and angina pectoris.
Isradipine, felodipine, levamlodipine, and nisoldipine are approved for hypertension only.
Nimodipine is used only for subarachnoid hemorrhage.
Clevidipine is used only for IV therapy of severe hypertension.
Recognize Cues
See nursing implications for Verapamil and Diltiazem.
Analyze Cues and Prioritize Hypotheses
Identifying High-Risk Patients
Use dihydropyridines with caution in patients with hypotension, sick sinus syndrome (in the absence of electronic pacing), angina pectoris (because of reflex tachycardia), heart failure, and second-degree or third-degree AV block.
Generate Solutions
Minimize Risks for Reflex Tachycardia
Reflex tachycardia can be suppressed with a beta blocker.
Minimize Risks for Peripheral Edema
Inform patients about signs of edema and instruct them to notify the prescriber if these occur. If necessary, edema can be reduced with a diuretic.
Take Actions
Route
Oral
All dihydropyridines except clevidipine.
Intravenous
Nicardipine, clevidipine.
Administration
Instruct patients to swallow SR formulations whole, without crushing or chewing.
Evaluate Outcomes
See nursing implications for Verapamil and Diltiazem.