Inotropic drugs

Discuss the uses, general drug action, general adverse reactions, contraindications, precautions, and interactions of the cardiotonic and inotropic drugs. 

Discuss important preadministration and ongoing assessment activities the nurse should perform on the patient taking a cardiotonic or inotropic drug. 

Acute Ml Use digoxin with caution in patients with acute Ml. The use of inotropic drugs in some patients in this setting may result in undesirable increases in myocardial oxygen demand and ischemia. 

Dopexamine, an agonist of cardiac /32-adrenoceptors and renal DAi-receptors, may be considered an inotropic drug with additional renal and peripheral vasodilator activities. Its duration of action is rather short and the drug is rarely used at present. 

Digitalis may be used in this stage for a reduction of hospitalization. However long-term infusion of positive inotropic drugs are harmful and their use is only indicated for palliation in end stage patient. 

Heart failure is a syndrome with many causes that may involve either ventricle or both. Cardiac output is usually below the normal range. Systolic dysfunction, with reduced cardiac output and significantly reduced ejection fraction (< 45%), is typical of acute failure, especially that resulting from myocardial infarction. Diastolic dysfunction often occurs as a result of hypertrophy and stiffening of the myocardium, and although cardiac output is reduced, ejection fraction may be normal. Heart failure due to diastolic dysfunction does not usually respond optimally to positive inotropic drugs. 

Contractility Heart muscle obtained by biopsy from patients with chronic low-output failure demonstrates a reduction in intrinsic contractility. As contractility decreases in the patient, there is a reduction in the velocity of muscle shortening, the rate of intraventricular pressure development (dP/dt), and the stroke output achieved (Figure 13-4). However, the heart is usually still capable of some increase in all of these measures of contractility in response to inotropic drugs. 

Other Positive Inotropic Drugs Used in Heart Failure... 

Paradoxically, these agents—not positive inotropic drugs—are the first-line therapies for chronic heart failure. The drugs most commonly used are diuretics, ACE inhibitors, angiotensin receptor antagonists, aldosterone antagonists, and blockers (Table 13-1). In acute failure,... 

Severe shock < 90 > 20 < 2.0 Vasoactive drugs, inotropic drugs, circulatory assist devices... 

Mitral regurgitation, < 100 > 20 < 2.5 Vasodilators, inotropic drugs, circulatory... 

The polypeptide ATX II has been found to have class III antiarrhythmic activity, indicating its potential in the management of cardiac arrhythmias [32]. A positive inotropic drug that was also effective as an antiarrhythmic might offer significant advantages therapeutically [33,34]. 

Dopamine and dobutamine are sometimes used to stimulate the heart in cases of acute or severe heart failure (see Chapter 20). Dopamine and dobutamine exert a fairly specific positive inotropic effect, presumably through their ability to stimulate beta-1 receptors on the myocardium.60 Other beta-1 agonists (epinephrine, prenalterol, etc.) will also increase myocardial contractility, but most of these other beta-1 agonists will also increase heart rate or have other side effects that prevent their use in congestive heart failure. Dopamine and dobutamine are usually reserved for patients with advanced cases of congestive heart failure who do not respond to other positive inotropic drugs (e.g., digitalis).6,72... 

Other drugs that may be prescribed in conjunction with diuretics for the treatment of CHF include vasodilators (drugs that dilate blood vessels, such as ACE inhibitors) inotropics (drugs that increase the heart s ability to contract, such as digoxin) and beta blockers (drugs that inhibit the action of epinephrine, such as carvedilol). 

Right ventricular infarct < 100 RVFP > 10 <2.5 Provide volume replacement for LVFP, inotropic drugs. Avoid diuretics. 

Approximately 25% of all patients with hypertrophic cardiomyopathy (HCM) have latent left ventricular outflow obstruction with an intraventricular gradient (I). Pathophysiologic features are asymmetric hypertrophy of the septum and a systolic anterior movement of the anterior leaflet. Medical treatment includes betablockers, and calcium antagonists of the verapamil type. Approximately 5— 10% of the patients with outflow obstruction are refractory to such negative inotropic therapy (2). Positive inotropic drugs such as digitalis or sympathomimetics are strictly contraindicated. In the presence of atrial fibrillation, anticoagulation therapy should be started. Since endocarditis is more common in patients with HCM because of turbulence in the left ventricle, prophylactic antibiotics should be administered for periods of potential bacteraemia. 

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