Arrhythmias causes

PSVT arising by reentrant mechanisms includes arrhythmias caused by AV nodal reentry, AV reentry incorporating an anomalous AV pathway, sinoatrial (SA) nodal reentry, and intraatrial reentry. 

Propranolol has been studied most carefully in experiments and in clinics. It is used for ventricular tachycardia, arrhythmia caused by digitalis drug overdose, or as a result of thy-rotoxosis or excess catecholamine activity. Despite the fact that there are a number of )8-adrenoblockers, propranolol is considered the first choice of drugs although other blockers of calcium blockers can be just as effective. 

This is primarily an anticonvulsant. Because of a wide range of toxic side effects its use as an antiarrythmic is limited to the treatment of arrhythmias caused by digitalis toxicity. Intravenous bolus injections can cause myocardial depression, hypotension, AV block and bradycardia. 

May be effective in atrial arrhythmias caused by digitalis. 

Calcium channel blockers decrease the rate of discharge of the SA node and inhibit conduction velocity through the AV node.5 These drugs are most successful in treating arrhythmias caused by atrial dysfunction, such as supraventricular tachycardia and atrial fibrillation.15,39... 

Actions Quinidine inhibits ectopic arrhythmias and ventricular arrhythmias caused by increased normal automaticity. Quinidine also prevents reentry arrhythmias by producing bidirectional block through decreasing membrane responsiveness and pro-... 

Actions Lidocaine, a local anesthetic, shortens phase 3 repoiarization and decreases the duration of the action potential (Figure 17.8). Unlike quinidine, which suppresses arrhythmias caused by increased normal automaticity, lidocaine suppresses arrhythmias caused by abnormal automaticity. Lidocaine, like quinidine, abolishes ventricular reentry. 

Correct answer = A. A bidirectional block can decrease arrhythmias caused by reentry. All antiarrhythmic drugs exert some negative inotropic effect and decrease cardiac output. The i side effects of this group of drugs are serious and include arrhythmias that can lead to sudden death. Some antiarrhythmic drugs affect K+ or Ca++ channels, or p adrenoreceptors. 

Browning JJ, Channer KS. Hyperkalaemic cardiac arrhythmia caused by potassium citrate mixture. BMJ (Clin Res Ed) 1981 283(6303) 1366. 

R-8I8 (17) prevented chloroform-induced ventricular fibrillation in mice as well as arrhythmias caused by hydrocarbon-epinephrine, ouabain, aconitine and coronary occlusion in dogs.5° The activity of numerous analogs in the mouse chloroform test has been described.57... 

In addition, to its hypotensive effect, rilmenidine has additional beneficial effects. In the cardiovascular field, it was shown to powerfully prevent the occurrence of experimental ventricular arrhythmias. Mammoto et al. (1996) reported that rilmenidine prevented the halothane-adren-aline induced arrhythmias in dogs. Our group has shown that rilmenidine was able to prevent the occurrence of ventricular arrhythmias caused by bicuculline injected i.c. in anaesthetized rabbits. This effect of potential clinical relevance was observed when rilmenidine was injected either i.c. or intravenously (Roegel et al., 1996). It is notable that this anti-arrhythmic action was observed at doses of rilmenidine too low to reduce blood pressure and that it was antagonized by idazoxan. Similar results were also obtained with moxonidine (Lepran and Papp, 1994 Mest et al., 1995). 

Antimuscarinic drugs are used as premedication to prevent salivation and bronchial secretions during an operation and to protect the heart from arrhythmias caused by inhalation anaesthetics such as halothane and propofol. They are less commonly used nowadays because modern anaesthetics are less irritant. 

Reports of cardiac arrhythmias caused by unusually high blood levels of two antihistamines, terfenadine and astemizole, led to their removal from the market. These effects were best explained by... 

B. Use with extreme caution in patients with arrhythmias caused by intoxication with cyclic antidepressants or type la or type Ic antiarrhythmic agents because of additive cardiac depression. 

A. To control excessive sinus tachycardia or ventricular arrhythmias caused by catecholamine excess (eg, theophylline or caffeine), sympathomimetic drug intoxication (eg, amphetamines, pseudoephedrine, or cocaine), or excessive myocardial sensitivity (eg, chloral hydrate, freons, or chlorinated and other hydrocarbons). 

---