W3 Cardiac Rhythms, Arrythmias, Anti-arrythmic drugs Flashcards
What are the symptoms of an MI?
How many types of MI are there?
- Severe chest pain
- Dyspnea
- Diaphoresis
- Nausea and vomiting
5 and also MI injury
What factors affect cardiac output? (4)
Pregnancy
Age
Exercise
Respiration
equation: CO= SV x HR
Which vessel supplies oxygenated blood to the SAN?
Right coronary artery
Setting the basic rhythm: cardiac pacemaker cells
- Intrinsic cardiac conduction system
- Autorhythmic pacemaker cells (1%)
- Unstable resting potential - Gap junctions
The heart contains:
-intracellular calcium channels (i.e. ryanodine receptors and inositol trisphosphate activated calcium channels)
-voltage dependent calcium channels in the plasma membrane (L-type channel)
which are important in controlling cardiac rate and rhythm
How many circuits in the heart?
How many coronary arteries are there?
2- pulmonary and systemic
4
L + R Coronary arteries
Left Circumflex Artery
Left Marginal Artery
Left Anterior Descending Artery
Setting the basic rhythm (latent fail safes)
(for info)
Sinus Node:
- Primary pacemaker
- Fires at a rate of 60-100 depolarisations per minute
AV node:
- Base of RA
- Fires at a rate of 40-60 dpm
Ventricular (Bundle of His)
- Right and left branches
- Fires at a rate of 20-40 dpm
Ventricular (Purkinje Fibers)
- Less than 40 dpm
Interpreting ECG:
P wave- Atrial depolarisation (hides atrial repolarisation)
QRS- Ventricular depolaristion
T- Ventriclular repolarisation
PR interval: roughly 200mm/sec
Factors affecting QT interval
(ECG)
- [Plasma Ca2+]
Hypercalcemia = short QT interval
Hypocalcemia = long QT interval - Medications – Amiodarone (affects ion channels)
- Genetics – mutations in LQT1, LQT2, LQT3
Ventricular tachycardia can lead to sudden cardiac death Torsades DE Pointes
What other conditions can ECG help to diagnose?
High blood pressure, emphysema
Some congenital heart abnormalities
Which interval on an ECG represents the time it takes for the atria and ventricles to depolarise and repolarise?
QT
What is the normal range of the QRS complex?
a) 0.06-0.1 sec
Which peak represents atrial depolarisation?
P wave
The ECG segments
PR segment
Pause between SA and AV node
ST segment
Should be at isoelectric line if elevated more than 2 small boxes (2mV) could signal issues infarction or ischaemia
PR Interval
(Normal 0.12-0.20s [3-5 little boxes])
SAN firing - depolarisation of atria - pause at AV node
QRS Interval
(Normal <0.10 [2.5 little boxes])
Depolarisation of the ventricles and repolarisation of the atria (pump efficiency)
QT Interval normal >440ms ♂ or >460ms ♀ @60bpm
N.B. RATE DEPENDENT need to calculate corrected QT (Bazett formula)
If QT prolonged then youre trying to contract a heart that is still trying to relax
atrial ectopic focus – depolaristaion occurs at a pacemaker cell (not SAN) close to or further away from AV node than the SAN
CORRECTED qt
Factors affecting QT interval
QT should be adjusted for heart rate but no one can decide on correct method
What are the features of an ECG of normal sinus rhythm?
Regular
Rate 60-100bpm
1 P wave for every QRS
QRS complex is narrow
PR interval <0.02s
What are the features of an abnormal ECG?
Characteristic shape-changein an ECG
Other conditions result in changes in cardiac rhythm (arrhythmias)
Acute impairment of blood flow to the heart (ischemia).
Prior, or evolving, acute myocardial infarction.
Abnormally fast, slow or irregular heart rhythms (arrhythmia).
Aberrant (abnormal) conduction of electrical activity through the heart
When may an arrythmia (abnormal heartbeat) occur?
- The heart’s natural pacemaker (the sinus node) becomes diseased and slows down
- The normal conduction pathway is interrupted
- Another part of the heart takes over as a pacemaker
What are the asymptomatic symptoms of an arrhythmia?
Palpitations
Signs of hypotension
Signs of dec brain perfusion
Tachycardia leading to Angina
Sudden cardiac death
What are the causes of arrythmias?
- Ischemia
- Hypoxia
- Acidosis or alkalosis
- Electrolyte abnormalities
- Excessive catecholamine exposure
- Autonomic influences
- Drug toxicity (eg digitalis or anti arrhythmic drugs)
- Overstretching of cardiac fibres
- The presence of scarred or otherwise diseased tissue
What are the 2 types of ventricular arrhythmias?
V-fibrillation (v-fib)
V-tachycardia (v-tach)
What is included in supraventricular arrythmia?
- Atrial fibrillation
- Atrial flutter
- Paroxysmal superventriculae tachycardia
(These occur above the ventricles and have a narrow QRS)
What is included in Ventricular Arrythmia?
Ventricular fibrillation
Ventricular tachycardia
(These occur below the ventricles and have a narrow QRS)
What type of arrhythmia is characterised by rapid and irregular heartbeats?
Ventricular fibrillation whereas SVT are regular although fast
What type of arrhythmia is characterised by a delay/blockage in the signals between the atria and the ventricles?
Atrioventricular block
What type of arrhythmia is characterised by uncoordinated and rapid contractions of the atria?
Atrial fibrillation
What type of arrhythmia is characterised by a slow heart rate?
Sinus bradycardia
What is the name of the Arrythmia when there is one or more abnormal heartbeats that exist in the ventricles?
Premature ventricular contractions (PVCs)
Rapid heartbeats originating above the ventricles?
Paroxysmal supraventricular tachycardia
Anti-arrhythmic drugs
Anti-arrhythmic drugs can be classified clinically into those that act on
* supraventricular arrhythmias (e.g. verapamil hydrochloride)
* both supraventricular and ventricular arrhythmias (e.g. amiodarone hydrochloride)
* ventricular arrhythmias (e.g. lidocaine hydrochloride)
Anti-arrhythmic drugs can also be classified according to their effects on the electrical behaviour of myocardial cells during activity (the Vaughan Williams classification)
Caused by:
(1) disturbances in
impulse formation (2) disturbancesin
impulse conduction (3) or both
Class 1 antiarrhythmic drugs
- Na+ channel blockers
- Dec Influx of Na+ into cardiac myocyte during Phase 0 – slower depolarisation
- Dec Conduction of AP thus wide QRS – slows heart rate
Class 1c – e.g. flecainide
What type of drug is it?
What does it manage? (2)
What is its MoA? (4)
Where is it contraindicated? (2)
- Na+ channel blockers.
- 3 classes all act on different electrical pathways, myocytes and membrane potentials
- Flecainide manages atrial fibrillation and paroxysmal supraventricular tachycardias (PSVT)
- …… markedly inhibit conduction through the His–Purkinjie system.
- Can cause arrhythmias
MoA
* …inhibits the action of sodium and potassium ion channels in the heart, raising the threshold for depolarisation (correcting arrhythmias)
* …slowly unbinds during diastole, prolonging the refractory period of the heart.
* This blockade also shortens the duration of action potentials through the Purkinjie fibers
* …blocks ryanodine receptor opening, reducing calcium release from sarcoplasmic reticulum, which reduces depolarization of cells
Contraindicated in
* ischaemic heart disease following MI can cause sudden cardiac death
* structural heart disease or left ventricular systolic dysfunction
Class IV antiarrhythmics: CCB Non-Dihydropyridine (Verapamil)
What are the adverse effects?
What are the drug interactions?
What are the contraindications?
Adverse effects:
* Heart block
* SA node depression
Interactions:
* Beta-blockers (decrease conduction velocity through AV node
-AV block
Contraindications:
* atrial flutter or fibrillation associated with accessory conducting pathways (e.g. Wolff-Parkinson-White-syndrome)
* Bradycardia
* cardiogenic shock
* heart failure (with reduced ejection fraction)
* history of significantly impaired left ventricular function
* hypotension;
* second- and third-degree AV block; * sick sinus syndrome;
* sino-atrial block
What are the 4 classes of anti-arrhythmic drugs?
- Na+ channel blockers
- BBs
- CCBs
- Unclassified e.g. digoxin, adenosine
Which drug class primarily acts by supressing phase 0 depolarisation of cardiac cells?
Class l
Which drug class primarily acts by blocking beta-adrenergic receptors in the heart?
Class ll (BB)
Which drug class acts by prolonging repolarisation and blocking potassium channels
Class lll (CCB)
Which drug class primarily acts by blocking calcium channels in cardiac cells?
Class lV
Which drug class primarily acts as other miscellaneous antiarrythmic agents?
Class lV
Amiodarone belongs to which anti arrhythmic drug class?
Class lll (CCBs)
Clinical significance:
What can be used to treat;
1. Supraventricular arrythmias? (3)
2. Supraventricular and ventricular arrythmias?
3. Ventricular arrythmias?
- Supraventricular arrhythmias
-Adenosine
-Verapamil (in asthma) but not if QRS is wide
-Digoxin - slows the ventricular response in cases of atrial fibrillation and atrial flutter - Supraventricular and ventricular arrhythmias
-Amiodarone hydrochloride may be given by intravenous infusion as well as by mouth, and has the advantage of causing little or no myocardial depression - Ventricular arrhythmias
-IV lidocaine hydrochloride - it is no longer the anti-arrhythmic drug of first choice
What are the types of AF?
Paroxysmal AF- episodes come and go, and usually stop within 48 hours without any treatment
Persistent AF- each episode lasts for longer than seven days (or less when it’s treated)
Long-standing persistent AF- continuous AF for a year or longer
Permanent-present all the time
Which of following is responsible for generating the first and second heart sounds?
- Closing of the AV valves.
- Opening of the AV valves.
- Opening of the semilunar valves.
- Closing of the semilunar valves.
- Closing of the AV valves
- Before the first heart sound is heard
Would the QRS complex in the ECG occur…
- After the first heart sound is heard?
- After the QRS complex
- Before the first heart sound is heard?
- After the T wave
3
In the electrocardiogram (ECG) of a normal cardiac cycle, the wave called T corresponds to
- Depolarization of the ventricles.
- Repolarization of the atria.
- Depolarization of the atria.
- Repolarization of the ventricles.
- Repolarisation of the ventricles
The cardiac cycle has two phases:
- Systole in which the atria contract; and diastole, in which the ventricles contract.
- Diastole, in which the atria relax; and systole, in which the ventricles relax.
- Diastole, in which the ventricles contract; and systole in which the ventricles relax.
- Systole in which the ventricles contract; and diastole, in which the ventricles relax.
4
Heart murmurs result from defective…
- Heart valves
- Arterioles.
- Ventricular contraction.
- Blood supply to the heart.
Heart valves
