Bradyarrhythmias

Lethal Arrhythmias. Arrhythmias are a second significant source of cardiovascular problems. An arrhythmia is an abnormal or irregular heart rhythm. Bradyarrhythmias result in heart rates that are too slow tachyarrhythmias cause abnormally fast rates. A bradyarrhythmia can be debiUtating, causing a person to be short of breath, unable to climb stairs, black out, or even to go into cardiac arrest. Tachyarrhythmias can be un settling and painful at best, life-threatening at worst. 

The first implantable pacemaker, introduced in 1960, provided a permanent solution to a chronic bradyarrhythmia condition. This invention had a profound impact on the future of medical devices. The pacemaker was the first implantable device which became intrinsic to the body, enabling the patient to lead a normal life. 

As of the mid-1990s, the market for bradyarrhythmia devices is hiUy penetrated in Western countries. Some growth is expected to result from an aging population but, by and large, the market is mature. The market for tachyrhythmia devices, in contrast, is only beginning. 

Dmgs that mimic or inhibit the actions of neurotransmitters released from parasympathetic or sympathetic nerves innervating the heart may also be used to treat supraventricular bradyarrhythmias, heart block, and supraventricular tachyarrhythmias. Those used in the treatment of arrhythmias may be found in Table 1. 

Isoproterenol. Isoproterenol hydrochloride is an nonselective P-adrenoceptor agonist that is chemically related to NE. It mimics the effects of stimulation of the sympathetic innervation to the heart which are mediated by NE. It increases heart rate by increasing automaticity of the SA and AV nodes by increasing the rate of phase 4 diastoHc depolarization. It is used in the treatment of acute heart block and supraventricular bradyarrhythmias, although use of atropine is safer for bradyarrhythmias foUowing MI (86). 

Normal rhythmic activity is the result of the activity of the sinus node generating action potentials that are conducted via the atria to the atrioventricular node, which delays further conduction to the His-Tawara-Purkinje system. From the Purkinje fibres, action potentials propagate to the ventricular myocardium. Arrhythmia means a disturbance of the normal rhythm either resulting in a faster rhythm (tachycardia, still rhythmic) or faster arrhythmia (tachyarrhythmia) or slowed rhythm (bradycardia, bradyarrhythmia). 

Block of propagation may occur in the specific conduction system leading to bradyarrhythmia... 

Numerous drugs ((1-blockers, diltiazem, verapamil, digoxin, and amiodarone) can cause bradyarrhythmias (sinus bradycardia and AV nodal blockade). 

Symptoms of bradyarrhythmias include dizziness, fatigue, lightheadedness, syncope, chest pain (in patients with underlying myocardial ischemia), and shortness of breath and other symptoms of heart failure (in patients with underlying left ventricular dysfunction). 

Cannot be made on the basis of symptoms alone, as the symptoms of all bradyarrhythmias are similar. 

Asymptomatic sinus bradyarrhythmias (heart rate less than 60 beats/min) are common especially in young, athletically active individuals. However, some patients have sinus node dysfunction (sick sinus syndrome) because of underlying organic heart disease and the normal aging process, which... 

Patients with bradyarrhythmias experience symptoms associated with hypotension such as dizziness, syncope, fatigue, and confusion. If LV dysfunction exists, symptoms of congestive HF may be exacerbated. 

Treatment of sinus node dysfunction involves elimination of symptomatic bradycardia and possibly managing alternating tachycardias such as AF. Asymptomatic sinus bradyarrhythmias usually do not require therapeutic intervention. 

Tachyarrhythmias -Bradyarrhythmias -Valvular heart disease (espec. AS) -Hypertrophic cardiomyopathy... 

Propofol is very lipid soluble, has a large volume of distribution, and has a rapid onset of action. It has comparable efficacy to midazolam for refractory GCSE. It has been associated with metabolic acidosis, hemodynamic instability, and bradyarrhythmias that are refractory to treatment. 

The onset of lactic acidosis often is subtle and accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, increasing somnolence, and nonspecific abdominal distress. There may be associated hypothermia, hypotension, and resistant bradyarrhythmias with more marked acidosis. The patient and the patient s physician must be aware of the possible importance of such symptoms. Instruct the patient to notify the physician immediately if these symptoms occur. Withdraw metformin until the situation is clarified. Serum electrolytes, ketones, blood glucose, and, if indicated, blood pH, lactate levels, and blood... 

Bradyarrhythmias - The usual IV adult dosage ranges from 0.4 to 1 mg every 1 to 2 hours as needed larger doses, up to a maximum of 2 mg, may be required. In children, IV dosage ranges from 0.01 to 0.03 mg/kg. 

Atarashi H, Endoh Y, Saitoh H, Kiashida H, Hayakawa H. Chronotropic effects of cilostazol, a new antithrombotic agent, in patients with bradyarrhythmias. J Car-diovasc Pharmacol 1998 31 534-9. 

Bradycardia can be due to depressed sinus automaticity and AV block. Bradyarrhythmias manifest as slow heart rate (less than 50 to 60 beats per minute in sleep). Depressed SA nodal automaticity lead to missing beats and bradycardia. AV block can be due to high vagal activity and side effect of certain drugs e.g. digitalis and P-blockers. 

Concomitant use with sympathomimetic drugs, p-adrenoceptor antagonists, calcium channel-entry blockers and other cardioactive drugs may result in bradyarrhythmias, bigemini, or tachyarrhythmias. Cardiac rhythm should be closely monitored and drug dosages carefully adjusted. Digoxin is mainly excreted by the kidneys and plasma levels should be closely monitored in patients with acute renal failure and in those whose renal function is compromised. 

Isoprenaline occasionally has a place in the management of cardiac conditions in which bradycardia is a feature, e.g. low cardiac output associated with slow heart rate after extracorporeal circulation in patients with excessive p-blocking therapy. It may also be used in the treatment of overdose with (3-adrenoceptor antagonists and for refractory bradyarrhythmias prior to cardiac pacing. Isoprenaline is used in the treatment of bronchial asthma on account of its 32 effects. 

Diltiazem appears to be similar in efficacy to verapamil in the management of supraventricular arrhythmias, including rate control in atrial fibrillation. An intravenous form of diltiazem is available for the latter indication and causes hypotension or bradyarrhythmias relatively... 

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