Ectopic: This is referred for those organs or parts of the body which occur not on their normal position. While denoting to heartbeat, this denotes to developing from other than the sinoatrial node.
Sunday, March 6, 2011
Effective refractory period
Effective refractory period: The time period in which there is weak conduction of impulses.
Adenosine
It is one of the naturally occurring nucleoside.
Action:
It causes a reduction in conduction velocity. It causes an increased refractory period and reduces automaticity in the AV node.
Pharmacokinetics:
Its duration of action is short. Its half life is approximately 10 seconds.
Therapeutic uses:
Acute supraventricular tachycardia (IV administration)
Adverse effects:
Flushing, chest pain, dyspnea, hypotension
Action:
It causes a reduction in conduction velocity. It causes an increased refractory period and reduces automaticity in the AV node.
Pharmacokinetics:
Its duration of action is short. Its half life is approximately 10 seconds.
Therapeutic uses:
Acute supraventricular tachycardia (IV administration)
Adverse effects:
Flushing, chest pain, dyspnea, hypotension
Digoxin
Action:
It causes a decrease in refractory period in atrial and ventricular cells of heart muscles. It causes an increase in effective refractory period and decreasing conduction velocity in AV node.
Therapeutic uses:
Atrial fibrillation and flutter (while controlling ventricular response rate).
Adverse effects:
It may cause ventricular beats originating from abnormal place. These beats may cause ventricular tachycardia and fibrillation. (treated with lidocaine or phenytoin)
It causes a decrease in refractory period in atrial and ventricular cells of heart muscles. It causes an increase in effective refractory period and decreasing conduction velocity in AV node.
Therapeutic uses:
Atrial fibrillation and flutter (while controlling ventricular response rate).
Adverse effects:
It may cause ventricular beats originating from abnormal place. These beats may cause ventricular tachycardia and fibrillation. (treated with lidocaine or phenytoin)
Verapamil and Diltiazem
Verapamil has major affect on heart muscles than on vascular smooth muscles. has major affect on heart muscles than on vascular smooth muscles.
Nifedipine has major affect on vascular smooth muscles than on heart. So, used to treat hypertension.
Diltiazem has medium affect.
Actions:
Calcium enters the cells through two channels:
1. Voltage sensitive channels
2. Receptor operated channels
The entry of calcium is controlled by the binding of agonists like catecholamines to the receptors.
Calcium entry blockers have pronounced effect on voltage sensitive channels leading to the slow influx of calcium resulting in contraction of cardiac muscles.
Verapamil and diltiazem gets bind to open, depolarized channels only, thus blocking the repolarization till the drug is dissociated from the channel.
They are therefore helpful only when there is rapid heart beat. (Normally, the calcium channels takes time for the repolarization until then the bound drug gets detached from the channel).
By reducing the inward flow, verapamil and diltiazem:
1. Decreases the conduction and
2. Increases the effective refractory period in AV node.
Therapeutic uses:
1. Atrial and ventricular arrhythmias
2. Reentrant supraventricular tachycardia
3. Decreases the ventricular rate in atrial flutter and fibrillation
4. Hypertension
5. Angina
Pharmacokinetics:
They are absorbed orally. Verapamil is extensively metabolized in the liver.
Adverse effects:
1. Negative inotropism
2. Reduces blood pressure (due to peripheral vasodilation. This effect is helpful in hypertension.)
Nifedipine has major affect on vascular smooth muscles than on heart. So, used to treat hypertension.
Diltiazem has medium affect.
Calcium enters the cells through two channels:
1. Voltage sensitive channels
2. Receptor operated channels
The entry of calcium is controlled by the binding of agonists like catecholamines to the receptors.
Calcium entry blockers have pronounced effect on voltage sensitive channels leading to the slow influx of calcium resulting in contraction of cardiac muscles.
Verapamil and diltiazem gets bind to open, depolarized channels only, thus blocking the repolarization till the drug is dissociated from the channel.
They are therefore helpful only when there is rapid heart beat. (Normally, the calcium channels takes time for the repolarization until then the bound drug gets detached from the channel).
By reducing the inward flow, verapamil and diltiazem:
1. Decreases the conduction and
2. Increases the effective refractory period in AV node.
Therapeutic uses:
1. Atrial and ventricular arrhythmias
2. Reentrant supraventricular tachycardia
3. Decreases the ventricular rate in atrial flutter and fibrillation
4. Hypertension
5. Angina
Pharmacokinetics:
They are absorbed orally. Verapamil is extensively metabolized in the liver.
Adverse effects:
1. Negative inotropism
2. Reduces blood pressure (due to peripheral vasodilation. This effect is helpful in hypertension.)
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