Cardio Concepts
Terms
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- Positive SA node influence
- B-adrenergic
- Negative SA node influence
- Vagal
- His-Perkinje influence
- B-adrenergic causes increased automaticity
- 3 things to slow pace of the heart?
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1. MDP more negative
2. Phase 4 depol. slower
3. Threshold more positive - EAD
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Early After Depolarization
-spon. depol. during phase 3
(muscle stretching, hypoxia) - DAD
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Delayed After Depolarization
-spon. depol. during phase 4
(B-adr, card. gly., extracellular ca) - 1st degree AV block
- long PR interval, benign
- 2nd degree AV block
- occasional missed beat
- Mobitz I AV block
- heart misses QRS-ventricular beat
- Mobitz II AV block
- QRS missed-at bundle of His
- 3rd degree AV block
- atrial beats do not go through AV node, waves independent of each other
- Atrial flutter
-
250-350 bpm, very rapid
**TX=propranolol, verapamil - Atrial fibrillation
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fibers stim too rapidly--no contraction
**TX=propranolol, anticoagulant - Supraventricular arrhythmia
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rapid premature contractions
TX: propranolol, verapamil
ACUTE TX: adenosine - Ventricular tachycardia
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180 bpm, dangerous, may lead to ventricular fib.
TX: lidocaine - Ventricular fibrillation
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no effective pumping, extremely dangerous, requires defibrillation
TX: epinephrine - Automaticity
- cells spontaneously reach threshold and fire action potentials (SA node=normal)
- Excitability
- tendency to fire at a given stimulus
- Autonomic effects
- w/ drugs: change heart rate, stroke volume and total peripheral resistance
- Treatment goals of anti-arrhythmia drugs (1)
- 1. Suppress abnormal automaticity (reduce ectopic pacemaking)
- Treatment goals of anti-arrhythmia drugs (2)
- 2. Correct abnormal impulse conduction (prevent reentry of impulses)
- Type I drugs
- Block sodium channels
- Type II drugs
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Block sympathetic effects
(Beta blockers) - Type III drugs
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Prolong refractory period
(Potassium channel blockers) - Type IV drugs
- Block calcium channels
- Sodium channel blocker actions
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1. reduce automaticity
2. reduce excitability
3. reduce reentry - Beta blocker actions
-
1. reduce automaticity
2. reduce excitability
3. reduce contractility
4. reduce reentry - IA Key
- inhibit sodium channels in active or damaged tissue
- IB Key
- have greater effects on damaged myocardium
- IC Key
- very slow off rates
- II Key
-
block sympathetic effects through inhibition of b-ad receptors
***dizziness, ED - Potassium channel blockers
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1. increases refractory period
2. little or no effect on automaticity or excitability - III Key
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prevent repolarization of channels
***can induce arrhythmias - Calcium channel blockers
-
1. reduce automaticity
2. minimal effects on excitability - IV Key
-
targets SA and AV nodal pacemaking cells
***reflex tachycardia - Adenosine treatment
-
PSVT, WPW syndrome
*causes no beat for a few seconds - CAST trial
-
BAD: encainide, flecainide, moricizine
GOOD: beta blockers - CHF
-
^ heart rate & O2 consumption
\/ stroke volume
heart swells, fluid accumulation - Digoxin MOA
-
^ intracellular Ca and contraction
**low K, high dig binding
TARGET=sod/pot pump - Control HR-sympathetic
- cardiac B1-increases cAMP
- Control HR-parasympathetic
- cardiac M2-decreases cAMP
- RX for CHF
- inotropic agents w/ vasodilator w/ diuretic
- Angina
- chest pain caused by coronary blood flow that is inadequate to meet the O2 demands of the myocardium
- Angina RX goals
- improve heart blood flow and reduce myocardial O2 requirement
- RX classes for angina
-
K channel openers
nitrates
ca channel blockers
ACE inhibitors
beta blockers - potassium channel openers
- diminished contraction, vasodilate
- Nitric oxide
- crucial mediator of VSMC tone
- nitrates
-
(generation of cGMP) relax arterial and venous smooth muscle
**can develop tolerance - calcium channel blockers-angina
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vasodilate-reduce afterload
**SE's: hypotension - ACE-I
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lower blood pressure
**SE's: cough (bradykinins in lungs), hypotension - ang II receptor blockers
-
lowers blood pressure
** hypotension but no cough - beta blockers-angina
-
takes work off heart by b1 and ang-ren system, decreases O2 req of heart
***do not use in diabetes, COPD - Hypertension def
- DBP is above 90 mmHg
- primary (essential) hypertension
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95% of cases
**worsened by obesity, smoking, and not enough exercise - secondary htn
-
5% of cases
**OCP's, pregnancy, renal disease - complications of htn
- CHF, renal failure, stroke
- non-RX TX of htn
- lose weight, reduce salt, reduce alcohol, stop smoking, do exercise
- 1st 3 RX's for HTN
- ACE, ARB, aldosterone antagonists
- 2nd 3 RX's for HTN
- diuretics, ganglionic blockers, beta blockers
- 3rd 4 Rx's for HTN
- alpha blockers, vasodilators, alpha 2 agonists in CNS, noradrenergic neuron blockers
- ganglionic blockers
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blocks autonomic system through nicotinic receptor
**used in emergency