Arrhythmias, cardiac drugs

Six helpful appendices are included Quick guide to cardiac arrhythmias summarizes the details of 20 arrhythmias Cardiac drug overview covers commonly used cardiac drugs Best monitoring leads shows the most beneficial leads to monitor for the most challenging arrhythmias Depolarization-repolarization cycle explains the five phases of this cardiac cycle Action potential curves reviews the cellular changes that occur during the depolarization-repolarization cycle and Cardiac conduction system reviews how electrical impulses affect heart function. 

When propranolol is administered orally for a less serious cardiac arrhythmia, cardiac monitoring is usually not necessary. The nurse should monitor the patient s blood pressure and pulse rate and rhythm at varying intervals, depending on the length of treatment and the patient s response to the drug. 

Fixed cardiac output Avoid use with fixed cardiac output because severe hypotension may result from a fall in peripheral resistance without a compensatory increase in cardiac output. If survival is threatened by arrhythmia, the drug may be used, but give vasoconstrictive catecholamines promptly if severe hypotension occurs. 

Contraindications for antipsychotic therapy are few they may include Parkinson s disease, hepatic failure, hypotension, bone marrow depression, or use of CNS depressants. Overdoses of antipsychotics are rarely fatal, except for thioridazine, which is associated with major ventricular arrhythmias, cardiac conduction block, and sudden death. For other agents gastric lavage should be attempted even if several hours have elapsed since the drug was taken, because gastrointestinal motility is decreased and the tablets may still be in the stomach. Moreover, activated charcoal effectively binds most of these drugs and can be followed by a saline cathartic. The hypotension often responds to fluid replacement or pressor agents such as norepinephrine. 

Contraindications Angle-closure glaucoma, blood dyscrasias, cardiac arrhythmias, cardiac or hepatic impairment, concurrent use of drugs that prolong QT interval, severe CNS depression... 

Problem/lnfluence of Medication. Propranolol and the other beta blockers are successful in reducing various supraventricular arrhythmias. These drugs, however, also attenuate the cardiac response to exercise. Heart rate and cardiac output are lower at any absolute workload, and maximal heart rate and cardiac output are attenuated by beta blockade. Consequently, the exercise response of a patient taking a beta blocker will be less than if the patient is not tak-... 

Interactions The vitamin pyridoxine (B6) increases the peripheral breakdown of levodopa and diminishes its effectiveness (Figure 8.6). Concomitant administration of levodopa and monoamine oxidase (MAO) inhibitors, such as phenelzine (see p. 124), can produce a hypertensive crisis caused by enhanced catecholamine production therefore, caution is required when they are used simultaneously. In many psychotic patients, levodopa exacerbates symptoms, possibly through the buildup of central amines. In patients with glaucoma, the drug can cause an increase in intraocular pressure. Cardiac patients should be carefully monitored because of the possible development of cardiac arrhythmias. Antipsychotic drugs are contraindicated in parkinsonian patients, since these block dopamine receptors and produce a parkinsonian syndrome themselves. 

Adverse effects. Halofantrine may cause gastrointestinal symptoms pruritis occurs but to a lesser extent than with chloroquine which may be reason for it to be preferred. It prolongs the cardiac QT interval and may predispose to hazardous arrhythmia. The drug should therefore not be taken ... 

Procainamide is a Type la antiarrhythmic agent used to treat supraventricular and ventricular arrhythmias. This drug is also used in the management of cardiac arrest. ... 

Many local anesthetics have a selective depressant action on heart muscle when given system cally. This is useful in t.reatment of cardiac arrhythmias, and a 1 idocaine-1 ike drug with this kind of action is tocainide (2). ... 

Antiarrhythmic drugs are substances that affect cardiac ionic channels or receptors, thereby altering the cardiac action potential or its generation or propagation. This results in changes of the spread of activation or the pattern of repolarization. Thereby, these drugs suppress cardiac arrhythmia. 

Ca2+ is an important intracellular second messenger that controls cellular functions including muscle contraction in smooth and cardiac muscle. Ca2+ channel blockers inhibit depolarization-induced Ca2+ entry into muscle cells in the cardiovascular system causing a decrease in blood pressure, decreased cardiac contractility, and antiarrhythmic effects. Therefore, these drugs are used clinically to treat hypertension, myocardial ischemia, and cardiac arrhythmias. 

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