Cardiac stimulants, also known as positive inotropes, are one of the mainstays in the treatment of cardiac insufficiency. When used correctly, they can often save a patient’s life on the first line. So what are the cardiac stimulants? And how are they used? Here we will talk about it. Cardiac drugs are divided into cardiac glycosides and non-cardiac glycosides. Cardiac glycosides, also known as digitalis, include digoxin, sildenafil and digitalis toxin. Their mechanism of action, common adverse effects and contraindications are similar. Mechanism of action 1. positive inotropic effect: inhibit Na+-K+-ATPase activity, increase Na+-Ca2+ exchange, increase Ca2+ concentration in cardiomyocytes, and strengthen the heart; 2. excite the vagus nerve to slow down the heart rate and negative conduction; 3. cardiac electrophysiological effect; 4. reduce the activity of the neuroendocrine system, and treat heart failure. Advantages: enhances the contractility of the heart of patients with congestive heart failure without increasing the oxygen consumption of their myocardium. Disadvantages: The therapeutic dose is close to the toxic dose, which can easily lead to fatal arrhythmias. Risk factors Low blood potassium, low blood magnesium, high blood calcium, myocardial ischemia and hypoxia, renal insufficiency, advanced age and unreasonable drug (such as drugs that lower blood potassium, etc.) combination, so that the blood electrolyte levels need to be checked before use. They also have their own characteristics, therefore, for different disease states, different cardiac glycosides can be used. For example, according to the speed of onset of action: toxin trichothecene K > cidilan (trichothecene C) > digoxin > digitalis toxin. Therefore, acute congestive heart failure can be chosen from poisonous trichothecene K, chronic heart failure is often chosen from digoxin, and cediran is suitable for critical and emergency patients, and can be used repeatedly and many times in a short period of time. For acute heart failure with rapid ventricular rate and atrial fibrillation, cediran 0.2-0.4 mg can be administered slowly intravenously, and 0.2 mg can be used again after 2-4 hours. For supraventricular tachycardia or ventricular rate control in atrial fibrillation, if you are not taking oral digitalis, the first dose of 0.4-0.6 mg can be administered slowly after dilution, and 0.2-0.4 mg can be given after 20-30 minutes if it is ineffective. If you are already taking digoxin orally, give 0.2 mg as the first dose, then increase the dose as appropriate. Digoxin is commonly used in heart failure and supraventricular tachycardia, often in combination with heart rate slowing drugs. It is particularly suitable for heart failure with reduced left ventricular ejection fraction (NYHA class II-IV); digoxin is not recommended for patients with NYHA class I cardiac function. It is also indicated for patients with LVEF ≤45% who are on diuretics, ACEI (or ARB), β-blockers and aldosterone receptor antagonists and still persistently symptomatic, and is particularly suitable for patients with atrial fibrillation with rapid ventricular rate. For control of ventricular rate in chronic AF in acute heart failure, digoxin or cetiran is preferred intravenously. Digoxin should not be easily discontinued in patients who are already on digoxin. Application: Use a maintenance dose of 0.125-0.25 mg/d, halving the dose in the elderly or in those with impaired renal function. The dose may be increased to 0.375-0.50 mg/d for control of rapid ventricular rate in atrial fibrillation. monitor for adverse effects. Digitalis toxin is slow and long-lasting, up to 14 days, and is not commonly used in clinical practice. However, because it is mainly metabolized in the liver, the metabolites are excreted via the kidney. It is suitable for patients with congestive heart failure with renal impairment. Oral adult dose: digitalis, total 0.7-1.2 mg, 0.05-0.1 mg orally every 6-8 hours; maintenance 0.05-0.1 mg a day. It should be noted that cardiac glycosides are not only useless but harmful when applied to hypertrophic cardiomyopathy, pulmonary heart disease and hypertensive heart disease. Therefore, the contraindications should be kept in mind: ventricular tachycardia, ventricular fibrillation; obstructive hypertrophic cardiomyopathy (except those with systolic insufficiency or atrial fibrillation); preexcitation syndrome with atrial fibrillation or flutter, all of which are contraindicated in patients. Non-cardiac glycosides include sympathomimetic amines, bipyridyl derivatives, calcium sensitizers, etc. Commonly used in acute heart failure or chronic heart failure deterioration, such as acute heart failure with low cardiac output syndrome, refractory end-stage heart failure, pulmonary hypertension with right heart failure, etc. Both sympathomimetic amines and bipyridyl derivatives increase intracellular cAMP concentration, thereby increasing intracellular Ca2+ concentration and enhancing myocardial contractility, as well as peripheral vasodilator effects. Short-term application has good hemodynamic effects, but it is important to note that long-term use increases mortality. Sympathomimetic amines The common drugs are dopamine and dobutamine. They are not recommended for patients receiving beta-blocker therapy. Dobutamine acts on dopamine receptors at low doses, on myocardial β1 receptors at moderate doses of 2-10 µg/kg-min, with positive inotropic effects, and on α receptors at high doses. Generally used to increase renal perfusion and renal flow in acute heart failure with impaired renal perfusion due to low blood pressure. Dosage: Start with 3 µg/kg-min and gradually increase the dose. Monitor SaO2 and administer oxygen if necessary. Dobutamine acts on β1 and β2 receptors in the myocardium to increase cardiac output and reduce peripheral resistance, with less effect on heart rate increase. Commonly used in decompensated heart failure with poor peripheral focus or poor diuretic effect. Side effects are mainly ventricular arrhythmias and aggravation of myocardial ischemia. Dosage: administered intravenously from 2 to 20 µg/kg-min. Monitor blood pressure carefully. Pulmonary hypertension with right heart failure can be used for a short period of time from 2 to 5 µg/kg-min. In the presence of septic shock, dobutamine is the antihypertensive agent of choice for CO reduction. When two conditions exist: 1, elevated cardiac filling pressures and reduced CO suggest myocardial dysfunction. 2. When signs of inadequate perfusion occur despite adequate blood volume and adequate MAP, dobutamine may be infused. Bipyridyl derivative Milrinone is a phosphodiesterase inhibitor that has a short-term effect on cardiac index and cardiac output. It can be used in decompensated heart failure undergoing beta-blocker therapy or for short-term use in patients with severe circulatory disorders who are intolerant to conventional therapy. Side effects are hypotension and tardive dyskinesia. Dosage: First dose 25-75 µg/kg intravenously (>10 min), followed by 0.375-0.75 µg-kg-1-min-1 intravenous drip. Calcium sensitizer Levosimendan is both a calcium sensitizer and a vasodilator and phosphodiesterase inhibitor. It is indicated for patients with low cardiac output due to systolic insufficiency but not hypotension. Can be used in patients receiving beta-blockers. Side effects are tachycardia and hypotension. Dosage: First dose of 12 µg/kg intravenously (>10 minutes), followed by 0.1 µg/kg-min intravenous drip. May be halved or doubled as appropriate. For patients with systolic blood pressure <100 mmHg, administer a maintenance dose directly to prevent hypotension. Monitor blood pressure and electrocardiogram carefully.