Cardiac abnormalities rhythm

These dm are primarily used in the treatment of hypertension (see the Summary Drug Table Adrenergic Blocking Drugs also see Chap. 39) and certain cardiac arrhythmias (abnormal rhythm of the heart), such as ventricular arrhythmias or supraventricular tachycardia They are used to prevent reinfarction in patients with a recent myocardial infarction (1—4 weeks after MI). Some of these dm have additional uses, such as the use of propranolol for migraine headaches and nadolol for angina pectoris. 

The sodium pump normally creates a small potential across cardiac cell membranes when digoxin blocks this pump, there is some depolarization of the cell. The heart then becomes more excitable and abnormal rhythms or ectopic beats may occur. Some patients also experience gastrointestinal disturbances, such as anorexia, nausea or vomiting. When blood concentration of digoxin is high, there may also be CNS effects, which can include confusion and visual disturbances. 

Paclitaxel causes disturbances in cardiac rhythm, but the relevance of these effects has not been fully elucidated. Originally, aU patients in trials of paclitaxel were under continuous cardiac monitoring, owing to the risk of hypersensitivity reactions, and cardiac disturbances were therefore more likely to be detected. Many trials limited eligibility to patients without a history of cardiac abnormalities and to those who were not taking medications likely to alter cardiac conduction. The incidence of cardiac dysrhythmias in the population under study not treated with paclitaxel is unknown, and it is therefore not always possible to attribute dysrhythmias to paclitaxel in these patients. The Cremophor EL vehicle does not appear to be implicated in the incidence of dysrhythmias, although hypotension associated with hypersensitivity reactions may occur (13). 

A 34-year-old man with migraine had palpitation after taking sumatriptan by nasal spray for a severe headache (13). A similar episode had occurred after he had previously taken sumatriptan. He had atrial fibrillation with a rapid ventricular rate. Sinus rhythm returned spontaneously within a few hours. No structural cardiac abnormality was detected. 

Lung biopsies performed in a small number of patients revealed a vasculitis and perivasculitis with a chronic interstitial pneumonitis. Disturbances of cardiac rhythm and conduction have also been documented. Examination of cardiac autopsy specimens has demonstrated neural lesions throughout the conduction system, similar to the neuropathology seen in skeletal muscle. Inflammatory lesions of the small coronary arteries were also present. The prevalence of cardiac abnormalities among all patients with EMS is unknown, although life-threatening rhythm disturbances appear to be uncommon. 

Under some pathophysiological conditions, a normal cardiac action potential may be interrupted or followed by an abnormal depolarization. If this abnormal depolarization reaches threshold, it may give rise to secondary upstrokes that can propagate and create abnormal rhythms. These abnormal secondary upstrokes occur only after an initial normal, or triggering, upstroke and so are termed triggered rhythms. 

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. 

Cardiac arrhythmias or dysrhythmias are disturbances of the normal regular rhythm which may be caused by an abnormality in the site of impulse generation, its rate or regularity, or its propagation or conduction (1,2). The more commonly encountered cardiac arrhythmias are... 

Cardiac-changes in pulse rate or rhythm electrocardiographic changes, such as bradycardia, tachycardia, premature ventricular contractions, bigeminal (two beats followed by a pause), or trigeminal (three beats followed by a pause) pulse. Other arrhythmias (abnormal heart rhythms)also may be seen. 

While the ECG is an invaluable tool for the observation of heart rate and rhythm, as well as for the diagnosis of conduction abnormalities, ischaemia, and infarcts, its detailed interpretation is not without pitfalls. One reason for this is that different changes in cardiac cellular behaviour may give rise to very similar effects on the ECG. This makes it difficult to draw conclusions from a patient s ECG to the underlying (sub-)cellular mechanisms. This issue is usually referred to as the inverse problem. ... 

Arrhythmia is defined as loss of cardiac rhythm, especially irregularity of heartbeat. This chapter covers the group of conditions caused by an abnormality in the rate, regularity, or sequence of cardiac activation. 

Monitoring - Laboratory test monitoring for liver abnormalities is appropriate. Rapid IV administration Rapid IV administration of cimetidine has been followed by rare instances of cardiac arrhythmias and hypotension. Bradycardia, tachycardia, and premature ventricular beats in association with rapid administration of IV ranitidine may occur rarely, usually in patients predisposed to cardiac rhythm disturbances. 

Andrew EE, John PD, Kenneth AE, et al. ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities. J Am Coll Cardiol. 2008 51 1-62. 

Propranolol is indicated in the management of a variety of cardiac rhythm abnormalities that are totally or partially due to enhanced adrenergic stimulation. In selected cases of sinus tachycardia caused by anxiety, pheochromocytoma, or thyrotoxicosis, (3-blockade will reduce the spontaneous heart rate. 

Cardiac arrhythmias is a group of disorder characterized by an abnormal cardiac rhythm and arise as a result of disorders of impulse formation or conduction or both. 

Question the need for therapy. The mere identification of an abnormality of cardiac rhythm does not necessarily require that the arrhythmia be treated. An excellent justification for conservative treatment was provided by the Cardiac Arrhythmia Suppression Trial (CAST) referred to earlier. 

Regardless of what the initiating factor is in producing arrhythmias, the mechanism underlying a disturbance in cardiac rhythm can be attributed to one of the three basic abnormalities listed below.5... 

Abnormal impulse generation. The normal automatic rhythm of the cardiac pacemaker cells has been disrupted. Injury and disease may directly render the SA and AV cells incapable of maintaining normal rhythm. Also, cells that do not normally control cardiac rhythm may begin to compete with pacemaker cells, thus creating multiple areas of automaticity. 

Cardiac arrythmias Abnormal beating rhythms in the heart. 

In some types of rhythm disorders, antiar-rhythmics of the local anesthetic, Na+-channel blocking type are used for both prophylaxis and therapy. These substances block the Na+ channel responsible for the fast depolarization of nerve and muscle tissues. Therefore, the elicitation of action potentials is impeded and impulse conduction is delayed. This effect may exert a favorable influence in some forms of arrhythmia, but can itself act arrhythmogenically. Unfortunately, antiarrhythmics of the local anesthetic, Na+-channel blocking type lack suf -cient specificity in two respects (1) other ion channels of cardiomyocytes, such as K1 and Ca+ channels, are also affected (abnormal QT prolongation) and (2) their action is not restricted to cardiac muscle tissue but also impacts on neural tissues and brain cells. Adverse effects on the heart include production of arrhythmias and lowering of heart rate, AV conduction, and systolic force. CNS side effects are manifested by vertigo, giddiness, disorientation, confusion, motor disturbances, etc. 

Q2 A defibrillator administers a large direct current (DC) shock (starting at 200 J) across the chest wall in order to depolarize the whole heart and stop the activity of the dysrhythmic areas, which are producing ectopic (abnormal) beats. It is hoped that this will allow the normal pacemaker, the SA node, to start again and generate the cardiac impulse in a normal rhythm this is known as sinus rhythm. 

Cardiac ischaemia may trigger abnormal electrical activity, causing fibrillation. Defibrillators deliver a large DC shock across the heart (cardioversion), to arrest abnormal activity and allow re-establishment of sinus rhythm. 

Q8 Depolarization of the atria normally gives rise to one P wave which precedes the QRS complex and a coordinated atrial contraction. In fibrillation the cardiac impulses arise abnormally and discharge at a very high rate (>350 min-1), producing a fast series of small, irregular waves before the QRS complex of the ECG. When this happens, the atria are unable to contract in a coordinated manner. Only occasional impulses can move through to the AV node to excite the ventricle, and ventricular rhythm becomes irregular. Patients become aware of the abnormal ventricular rhythm and usually describe the sensation as palpitations . 

Q12 Digoxin has a low or narrow therapeutic index, which means that the therapeutic concentration of the drug is close to a concentration that elicits toxicity. A particular problem with digoxin is the production of abnormal cardiac rhythms. 

In a retrospective review of all dysrhythmias in children with prenatal cocaine exposure, 18 cases were detected in 554 infants who had positive urine screens for cocaine (318). In 13 neonates the dysrhythmia occurred beyond the period of direct cocaine exposure and six of the children had dysrhythmias after the neonatal period. Most of the dysrhythmias were supraventricular extra beats. Overall, the rate of consultations for dysrhythmias was higher among cocaine-exposed neonates than expected. Some cocaine-exposed children had symptomatic dysrhythmias that were persistent or recurrent and required treatment to maintain cardiac output and restore normal cardiac rhythm. Children who were exposed prenatally to cocaine appeared to be at increased risk of abnormal responses to stress, manifested by symptomatic dysrhythmias beyond the period of cocaine exposure. 

Less common effects of Lyme disease are heart abnormalities (such as irregular rhythm or cardiac block) and eye abnormalities (such as swelling of the cornea, tissne, or eye muscles and nerves). 

Direct current (DC) electric shock applied externally is often the best way to convert cardiac arrhythmias to sinus rhythm. Many atrial or ventricular arrhythmias start as a result of transiently operating factors but, once they have begun, the abnormal mechanisms are self-sustaining. When a successful electric shock is given, the heart is depolarised, the... 

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