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Flashcards in Class IV Deck (10):
1

Class IV agents - general

Verapamil, Diltiazen

- Ca2+ channel antagonists (cardiac)

--> similar in utility to class II agents with priamry effects on nodal phase 0 depolarization

--> DEPRESSED SA nodal automaticity, AV nodal conduction, decreased ventriucalr contractility

2

describe general of calcium channel blockers (CCBs)

- Ca2+ channel blockers interfere with the entry of Ca2+ into cells through voltage-dependent L- and T-type Ca2+ channels

- Major cardiovascular sites of action

--> vascular smooth muscle cells

--> cardiac myocytes

--> SA and AV nodal cells

- binding to specific sites in Ca2+ channel subuts, CCB DIMINISH THE DEGREE TO WHICH THE CA2+ CHANNEL PORES OPEN IN RESPONSE TO VOLTAGE DEPOLARIZATION

3

describe L-type Ca2+ channel

- L-type Ca2+ channel alpha1 subunit

- alpha 1 contains pores

- NO CCB binds to all pores --> blockade is incomplete

4

what are the main clases of CCB

- Dihydropyridine (DHP)

- NIFEDIPINE = effects mainly in the vasculature

- Non-dihydropyridine (NDHP)

- Verapamil = effects mainly HEART

- Diltiazem = effects mainly HEART

5

describe the major cardiovascular actions of CCB

- VASODILATION = more makred in arterial and arteriolar vessels than on veins

- NEGATIVE CHRONOTROPIC AND DROMOTOROPIC EFFECTS (NDHP agents only)

--> seen on SA and AV nodal conducting tissue

- NEGATIVE INOTROPIC EFFECTS

--> seen on myocardial cells

--> in case of DHPs, this effect may be offset by REFLEX ADRENERGIC STIMULATION AFTER PERIPHERAL VASODIALTION

6

describe non-cardiovascular effects of CCB

- Little or no effect on other smooth muscles

- Relax uterine smooth muscle and has been used in therapy for preterm contractions

- SKELETAL MUSCLE DOES NOT RESPOND TO CONVENTIONAL CCBS

7

describe the main clinical applications of CCB

- Systemic hypertension

- angina pectoris

- supraventricular tachycardia

- post-infarct protection

8

describe MoA  VERAPAMIL

- Slow inward Ca2+ channels in nodal tissue are primarily affected

- DECREASE SA AUTOMATICITY --> DECREASED HR

- DECREASED AV CONDUCTION --> increased PR interval

- Cardiac depression (decreased ventricular contractility and HR)

- no effect on ventricular Na+ conduction = ineffective on ventricular arrhythmia

 

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9

Applications of verapamil

- supraventricular tachycardia (IV = conversion; PO = maintenance)

- RATE CONTROL in Atrial fibrillation

- angina pectoris

- hypertension

10

describe the adverse effects of verapamil

- ADVERSE

--> headache, flushing, dizziness, ankle edema

--> CONSTIPATION

--> EXACERBATE CHF

- hypotension (IV)

- AV heart block in combo with Beta-blockers

- CONTRAINDICATIONS

--> WPW syndropme with Afib

--> VENTRICULAR TACHYCARDIA