Antidysrhythmics
Antidysrhythmics are drugs that restore normal cardiac rhythm and are used to
treat cardiac dysrhythmias. A cardiac dysrhythmia is a disturbed heart rhythm.
It is also known as arrhythmia—absence of heart rhythm. A disturbed heart
rhythm is any deviation from the normal heart rate or heart pattern including
slow rates (bradycardia) and fast rates (tachycardia). The electrocardiogram
(ECG) is used to identify the type of dysrhythmia.
Table 19-2 lists the actions of antidysrhythmics and Table 19-3 describes
classes of antidysrhythmic drugs.
CHAPTER 19 Cardiac Circulatory Medications^353
Drug Group Variant (Vasospastic) Angina Classic (Stable) Angina
Nitrates Relaxation of coronary arteries, Dilation of veins, which decreases
which decreases vasospasms preload and decreases oxygen demands
and increases oxygen supply
Beta blockers Not effective Decreases heart rate and contractility,
which decreases oxygen demand
Calcium Relaxation of coronary arteries, Dilation of arterioles, which decreases
channel which decreases vasospasms after load and decreases oxygen
blockers and increases oxygen supply demand. Verapamil and diltiazem
decrease heart rate and contractility.Table 19-1. Effects of antianginal drugs on angina.
Mechanisms of Action
Block adrenergic stimulation of the heart
Depress myocardial excitability and contractility
Decrease conduction velocity in cardiac tissue
Increase recovery time (repolarization) of the myocardium
Suppress automaticity (spontaneous depolarization to initiate beats)Table 19-2. Antidysrhythmic actions.