case 8 - palpitations Flashcards
What type of cells make up the SA node?
Pacemaker cells
What features of pacemaker cells makes them able to generate action potentials spontaneously?
They have a resting membrane potential that is less negative than cardiomyocytes
What CNS inputs control the rate of SA node discharge?
Autonomic inputs - sympathetic and parasympathetic
Which nerve fibres slow heart rate?
Parasympathetic fibres, via the vagus nerve
Which nerve fibres increase heart rate?
Sympathetic fibres, via the cardiac nerves
How do parasympathetic inputs to the SA node slow heart rate?
They reduce the slope of the pacemaker potential and hyperpolarise the node, making it take longer to reach the threshold potential.
How do sympathetic inputs to the SA node increase heart rate?
They release noradrenaline which bind to B1 adrenergic receptors which increase the slope of the pacemaker potential, making it easier for pacemaker cells to reach threshold and fire.
What is the pathway of conduction through the heart, starting at the SA node?
SA node, AV node, Bundle of His, Left & Right Bundle branches, Purkinje fibres
What is the most common type of aryhthmia?
Atrial fibrillation
What is the nature of function of the atria during atrial fibrillation?
Contractions of the atria are rapid, non-functional. Multiple atrial foci discharge simultaneously causing fibrillation
What is fibrillation?
Rapid, muscular twitching involving individual fibres acting without coordination
Why does atrial fibrillation increase the risk of ischaemic stroke?
The left atrial appendage cannot empty properly when the atria are fibrillating, resulting in stasis within it, which increases the risk of thrombus formation
How is the regularity of the rhythm in Atrial Firllation described?
Irregularly irregular
What are the key characteristics of an irregularly irregular rhythm?
Irregularly spaced QRS complexes, with no temporal pattern to the complexes.
What are the characteristics of an ECG of atrial fibrillation?
Absent P waves, narrow irregularly irregular QRS complexes, tachycardia
Are patients in atrial fibrillation typically tachycardic or bradycardic?
Tachycardic
What are the common symptoms of atrial fibrillation?
Palpitations, dyspnoea, fatigue
Which procedure uses electrical current to re-establish sinus rhythm in patients with atrial fibrillation?
Cardioversion
What is the process of cardioversion?
Short acting anaesthetic given, electrodes applied to back and chest, shock coinciding with R wave on ECG
At which point on the ECG is a shock administered during cardioversion?
Coinciding with R wave
What is the key risk associated with cardioversion, and how is this mitigated?
Embolism - risk factors considered, anti-coags/anti-platelets administered.
What are the 3 key components to comment on when interpreting waves/complexes on an ECG?
rate, regularity, morphology
What are the 5 key classes of cardiovascular drugs?
ACE inhibitors, ARBS, Calcium Channel Blockers, Diuretics, Beta Blockers
What is the full name for ACE inhibitors?
Angiotensin Converting Enzyme Inhibitor
What do ACE inhibitors inhibit?
Vascular Angiotensin Converting Enzymes
What is the mechanism of action of ACE inhibitors?
They inhibit vascular ACE enzymes, which are required for the conversion of Angiotensin I to Angiotensin II. Reduced Ang II reduces systemic vascular resistance and increases vasodilation via bradykinin. Ang II action on the kidneys lowers, promoting Na+ and H2O excretion to drop plasma volume.
What is a commonly used ACE inhibitor in NZ?
Enalapril, quinapril
What are the therapeutic indications for ACE inhibitors?
Hypertension, Chronic heart failure, atrial fibrillation, post-MI
What is the key contraindication for ACE inhibitors?
Renal Artery Stenosis
What is the full name of ARBs?
Angiotensin Receptor Blockers
What is the mechanism of action of ARBs?
Selective AT1 receptor antagonists, that block the effects of Ang II, therefore causing vascular dilation, increased Na+ and H2O secretion, leading to decreased preload and a drop in blood pressure.
What is the first line drug class used for the treatment of hypertension (unless contraindicated)?
ACE inhibitors
What are the therapeutic uses of ARBs?
Hypertension, Heart Failure
What are the contraindications for ARBs?
Renal Artery stenosis
What is the mechanism of action of calcium channel blockers?
The antagonise L-type Calcium channels, to prevent Ca2+ entry to vascular smooth muscle, cardiac muscle, and SA/AV nodal tissues, resulting in vasodilation, reduced force & rate of contraction and reduced conduction velocity to the ventricles.
What are the 3 key -tropic effects of calcium channel blockers on the heart?
Negative inotropic (reduced force of contraction)
Negative chronotropic (reduced rate of contraction)
Negative dromotropic (reduced conduction velocity to the ventricles)
What are the 2 types of selectivity of calcium channel blockers?
Vasoselective, cardioselective
What selectivity of calcium channel blocker is used to treat hypertension?
Vasoselective
What selectivity of calcium channel blocker is used to treat arrhythmias?
cardioselective
What selectivity of calcium channel blocker is used to treat angina?
Cardioselective
Which calcium channel blocker is the first line treatment for arrhythmia?
Diltiazem
What are the therapeutic uses of calcium channel blockers?
Hypertension, arrhythmia, angina
What is a key example of a vasoselective calcium channel blocker, used to treat hypertension?
Amlodipine
What is the general mechanism of action of diuretics?
They decrease Na+ and H2O reabsorption in the tubules, with different classes acting on different parts of the Loop of Henle
What are the key types of diuretic?
Osmotic, Loop, Thiazide, Thiazide-like, potassium sparing.
What is a key example of an osmotic diuretic?
mannitol
What is a key example of a loop diuretic?
Frusemide
What is the mechanism of action of loop diruetics?
They bind reversibly to carreir proteins in the loop of Henle, reducing Na+ reabsorption, and therefore reducing H2O reabsorption.
What are the therapeutic uses for diuretics?
Emergency reduction of intercranial pressure, hypertension, oedema.
What is the key contraindication for diuretics?
Gout
What is the mechanism of action of beta blockers?
Reversibly antagonise binding of adrenaline and noradrenaline to Beta receptors (B1 (+ B2)), to reduce cardiac output and blood pressure.
What are the two forms of selectivity of beta blockers?
Selective (for B1 receptors), Non-selective (for B1, B2 and a1 receptors)
What is the most commonly used selective Beta Blocker?
Metoprolol
What is a commonly used non-selective Beta Blocker?
Carvedilol
What are the therapeutic uses of beta blockers?
Cardiac rate control/arryhthmia, angina, heart failure, hypertension (occasionally)
What are the contraindications for Beta Blockers?
Asthma, peripheral vascular disease, heart block
What are the 3 key components of atrial fibrillation treatment?
Rate control, sinus rhythm maintenance, stroke prevention
What are the pharmacological treatments for rate control in AF?
Beta-Blockers, Calcium Channel Blockers, Digoxin
What are the non-pharmacological treatments for rate control in AF?
Ablation, pacemaker
What are the pharmacological treatments for sinus rhythm maintenance in AF?
Antiarhythmics - sodium channel antagonists, beta blockers, amiodarone
What are the non-pharmacological treatments for sinus rhythm maintenance in AF?
Catheter ablation, cardioversion, pacemaker, surgery
What are the pharmacological treatments for stroke prevention in AF?
Vitamin K antagonists (e.g. warfarin),
direction thrombin inhibitors (e.g. dabigatran)
What are the non-pharmacological treatments for stroke prevention in AF?
Surgical isolation of the left atrium
Why is warfarin used in treatment of atrial fibrillation?
It is an anti-coagulant, so reduces the risk of thrombus formation in the atrial appendages, and therefore lessens the likelihood of iscahemic stroke.
What is the mechanism of action of warfarin?
Inhibits the synthesis of Vitamin K, which is required for the activation of the clotting factors X, IX, VII and II (thrombin) and Protein C and S via gamma-carboxylation. It therefore interrupts clotting via the intrinsic pathway.
How can warfarin therapy be reversed?
Vitamin K injection, or if severe, infusion of the depleted factors.
