Drugs Affecting Rate and Force Flashcards
Is increased heart rate a positive or negative chronotopic effect?
Positive
What is automaticity and does it increase or decrease in sympathetic stimulation of B1 receptors?
tendency for non-nodal regions to acquire spontaneous activity, increases
Does cardiac efficiency increase or decrease with sympathetic stimulation?
Decrease (with respect to 02 consumption)
When pacemaker potential slope is decreased what happens to heart rate?
decreases
In parasympathetic division, which muscarinic cholinoceptors are activated to decrease heart rate?
M2
Which type of stimulation (parasympathetic or sympathetic) may cause dysrhythmias to occur in atria?
Parasympathetic
What current are pacemaker potentials regulated by?
Funny current
What are the channels that mediate the funny current called?
HCN gated channels
What mediate HCN gated channels?
Hyperpolarization and Cyclic AMP
What does block of HCN channels do to slope of pacemaker potential and heart rate?
decreases both
What is an example of a HCN channel blocker and what is it used for?
Ivabradine, angina
Describe the steps of excitation contraction coupling in cardiac muscle contraction.
- Ventricular action potential
- Opening of voltage activated calcium ion channels (mainly L-type)
- Calcium ion influx into cytoplasm
- Calcium is released from sarcoplasmic reticulum
- Cross bridge formation between actin and myosin results in contraction
What happens in excitation contraction coupling to cause relaxation?
Repolarization to phase 4, calcium ion channels closed, no calcium ion influx, no calcium released from sarcoplasmic reticulum, cross bridge formation between actin and myosin breaks, resulting in relaxation
Does increased calcium ion sensitivity cause enhanced or reduced contractility and which adrenoceptor is involved?
Enhanced, B1
What do Dobutamine, adrenaline and noradrenaline (catecholamines) do to cardiac efficiency?
reduce it
What do Dobutamine, adrenaline and noradrenaline (catecholamines) do to force, rate and cardiac output?
Increase it
What is adrenaline used for clinically?
cardiac arrest (sudden loss of pumping function) emergency treatment of asthma anaphylactic shock (life threatening respiratory distress and often vascular collapse)
What is dobutamine used for clinically and what beta receptor does it act on?
acute, but potentially reversible, heart failure (e.g. following cardiac surgery, or cardiogenic shock), B1
What does propanolol block?
B1 and B2
What to metopralol and atenolol block?
B1 only
What are adverse effects of beta-blockers?
bronchospasm, hypoglycaemia, aggregation of heart failure, fatigue, cold extremities, bradycardia
What does atropine do?
Increases heart rate, no effect on bp
Who does atropine have a more pronounced effect in?
Athletes
What is atropine used for clinically?
Reverse bradycardia following an MI, to accompany an analgesia, and in anticholinesterase poisoning
With heart failure is ventricular function curve elevated or depressed?
depressed
What type of drug is digoxin?
inotropic
Does digoxin enhance or decrease contractility?
enhance
Where can digoxin be found in nature?
Fox gloves
In presence of digoxin what happens to Na+/K+ATPase?
blocked
What happens to storage of calcium ions in the sarcoplasmic reticulum when using digoxin?
increases
How does digoxin work?
Binds to the alpha-subunit of Na+/K+ ATPase in competition with K+
In what circumstance may digoxin be dangerously enhanced?
Hypokalaemia
What does digoxin do to action potential and refractory period?
reduce
When is refractory period delay particulary useful (the combination of a and b)?
heart failure and AF
What are 2 of the most serious side effects of digoxin?
excessive depression of AV node conduction (heart block)
propensity to cause dysrhythmias
What type of drugs are calcium sensitizers e.g. levosimendan?
inotropic drug
How do calcium sensitizers cause vasodilation?
open Katp channels
Which class of anti-arrythmic is divided into 3 subclasses?
1
