Category: Fundamentals
Sodium channel blockers (class I antiarrhythmics) block cardiac sodium channels. By doing so, these drugs slow impulse conduction in the atria, ventricles and His-Purkinje system. Class I constitutes the largest group of antidysrhythmic drugs.
Category: Fundamentals
Reentry, also referred to as recirculating activation, is a generalized mechanism by which dysrhythmias can be produced. Reentry causes dysrhythmias by establishing a localized, self-sustaining circuit capable of repetitive cardiac stimulation.
Category: Fundamentals
Dysrhythmias arise from two fundamental causes: disturbances of impulse formation (automaticity) and disturbances of impulse conduction. One or both of these disturbances underlie all dysrhythmias.
Category: Fundamentals
Fast potentials occur in fibers of the His-Purkinje system and in atrial and ventricular muscle. These responses serve to conduct electrical impulses rapidly throughout the heart. Slow potentials occur in cells of the SA node and AV node.
Category: Fundamentals
In the healthy heart, impulses arriving at the AV node are delayed before going on to excite the ventricles. This delay provides time for blood to fill the ventricles prior to ventricular contraction.
Category: Fundamentals
The half-life of digoxin is about 1.5 days. In the absence of a loading dose, about 6 days (four half-lives) are required to reach plateau. When use of the drug is discontinued, another 6 days are required for digoxin stores to be eliminated.
Category: Fundamentals
In contrast to the thiazides and loop diuretics, the potassium-sparing diuretics promote only scant diuresis. In patients with HF, these drugs are employed to counteract potassium loss caused by thiazide and loop diuretics.
Category: Fundamentals
Loop diuretics produce profound diuresis. In contrast to the thiazides, these drugs can promote fluid loss even when GFR is low. Hence, loop diuretics are preferred to thiazides when cardiac output is greatly reduced.
Category: Fundamentals
Thiazide diuretics produce moderate diuresis. These oral agents are used for long-term therapy of HF when edema is not too great. Since thiazides are ineffective when GFR is low, these drugs cannot be used if cardiac output is greatly reduced.
Category: Fundamentals
Diuretics are first-line drugs for all patients with signs of volume overload or with a history of volume overload. By reducing blood volume, these drugs can decrease venous and arterial pressure, pulmonary and peripheral edema plus cardiac dilation.
Category: Fundamentals
Calcium channel blockers can cause reflex tachycardia. This reaction is greatest with the dihydropyridines and minimal with verapamil and diltiazem. Reflex tachycardia is low with verapamil and diltiazem because of cardiosuppression.
Category: Fundamentals
The baroreceptor reflex frequently opposes our attempts to reduce BP with drugs. Opposition occurs because the “set point” of the baroreceptors is high in people with hypertension. That is, the baroreceptors are set to perceive high BP as “normal.”
Category: Fundamentals
Nitroprusside is used to lower blood pressure rapidly in hypertensive emergencies. Oral antihypertensive medication should be initiated simultaneously. During treatment, furosemide may be needed to prevent excessive retention of fluid.
Category: Fundamentals
Hydralazine can cause an acute rheumatoid syndrome that closely resembles systemic lupus erythematosus (SLE). Symptoms include muscle pain, joint pain, fever, nephritis, pericarditis and the presence of antinuclear antibodies.
Category: Fundamentals
By lowering arterial BP, hydralazine can trigger reflex stimulation of the heart, causing myocardial oxygen demand to increase. Because hydralazine-induced reflex tachycardia is severe, the drug is usually combined with a beta blocker.
Category: Fundamentals
Hydralazine (Apresoline) causes dilation of arterioles. The drug has little or no effect on veins. Arteriolar dilation results from action on vascular smooth muscle. Because hydralazine acts selectively on arterioles, postural hypotension is minimal.
Category: Fundamentals
Prolonged use of arteriolar or venous dilators can cause an increase in blood volume (secondary to prolonged reduction of blood pressure). The increase in volume represents an attempt by the body to restore blood pressure to pretreatment levels.
Category: Fundamentals
Vasodilators differ from one another with respect to the types of BV they affect. Some agents (hydralazine) produce dilation of arterioles. While others (nitroglycerin) produce dilation of veins. Some (prazosin) can dilate arterioles and veins.
Category: Fundamentals
Like verapamil, digoxin suppresses impulse conduction through the AV node. Accordingly, when these drugs are used concurrently, the risk of AV block is increased. Patients receiving the combination should be monitored closely.
Category: Fundamentals
Verapamil is used to slow ventricular rate in patients with atrial flutter, atrial fibrillation and paroxysmal supraventricular tachycardia. Benefits derive from suppressing impulse conduction through the AV node.
