Case 13 Flashcards
Ionic current responsible for phase 4 of myocyte action potential
Ik1 - Inwardly rectifying potassium channels
Ionic current responsible for phase 0 of myocyte action potential
INa - Influx of sodium into cell
Ionic current responsible for phase 1 of myocyte action potential
Ito - Transient outward movement of potassium ions
Ionic current responsible for phase 2 of myocyte action potential
ICa,L - longlasting, inward movement of calcium
Ikr and Iks - rapid and slow outward movement of K+
Ionic currents increased by B-adrenergic stimulation
Iks, Ik1 and ICa,L
Calcium to a lesser extent than potassium
Effect of B-adrenergic stimulation on myocyte action potential
Shortens phase 2
Greater activation of potassium channels than calcium. So phase 2 ends sooner
Ryanodine receptor (RyR2)
Release of calcium in sarcoplasmic reticulum into sarcoplasm
Calsequestrin
Binds Ca2+ in SR lumen
FKBP
Inhibits RyR2
Dissociates from RyR2 on B-adrenergic stimulation - no longer inhibiting it.
SERCA2a
Ca2+ ATPase
In SR
Transports 2x Ca2+ per ATP
PMCA
Ca2+ ATPase
In sarcolemma (plasma membrane)
Transports 1x Ca2+ per ATP
Phospholamban
Regulator of SERCA2a
Calmodulin
Regulator of PMCA
Causes removal of Ca2+ when activated
Effect of sympathetic stimulation on phospholamban
Phospholamban is phosphorylated by PKA
Becomes less inhibitory of SERCA2a
TnT
Troponin which binds tropomyosin
TnC
Troponin which binds calcium
Effect of Ca2+ binding to TnC
Myosin and actin are able to interact
When TnI is phosphorylated by PKA
Sensitivity of myofilaments to Ca2+ is decreased
HCN channels
Hyperpolarisation-activated Cyclic Nucleotide-gated
Cause there to be an unstable resting potential (funny current)
Ionic current responsible for phase 4 of pacemaker action potential
If
Inward movement of Na+ via HCN channels
Ionic current responsible for phase 0 of pacemaker action potential
ICa,L
Inward movement of Ca2+
Ionic current responsible for phase 3 of pacemaker action potential
Ikr and Iks
Outward movement of K+
What is happening in the SAN to bring about tachycardia?
Increased binding of cAMP to HCN4 channels.
Increased Na+ entry into SAN cells.
Increased steepness of pacemaker potential.
What is happening in SAN to bring about bradycardia?
Decreased binding of cAMP to HCN4 - flattening of pacemaker potential.
Increased KACh (outward K+ current) - hyperpolarisation, takes longer for membrane potential to reach threshold.
I ncx (Ionic Current NCX)
Inward current via 3Na+(out)/Ca2+(in) exchange
I Ca,T (Ionic current Ca,T)
Inward T-type Ca2+ currents
Activated at negative potentials
Inactivated rapidly
I Kr (Ionic current Kr)
hERG channels
Associated with LQT2
I Ks (Ionic current Ks) channels are associated with…
LQT1
Dromotropic agents affect..
Conduction speed in AVN
High conductance connexins
Cx40 and Cx43
Low conductance connexins
Cx30 and Cx45
Connexins expressed by AVN
Cx30 and Cx45
Activated tropomyosin…
Blocks actin from binding to myosin
Troponin:Ca2+ complex…
Pulls tropomyosin away from actin’s myosin binding site
In smooth muscle, calcium binds to…
Calmodulin
Calcium:Calmodulin complex in smooth muscle cells activates…
MLCK
Smooth muscle cross bridge activity is turned on by Ca2+-mediated changes in…
Thick filaments
Myosin
Skeletal muscle cross bridge activity is turned on by Ca2+-mediated changes in…
Thin filaments
Actin
Normal AVN delay
0.12-0.2s
On an ECG, AVN delay is represented by…
PR interval
Conduction velocity in Bundle of His
1m/s
Conduction velocity in Purkinje Fibres
5m/s
Why is conduction velocity higher in Purkinje Fibres than in Bundle of His?
Larger diameter
Mechanism for AVN reentry tachycardia
Activation enters AVN via slow pathway.
Retrogradely activates atria via fast pathway.
AVRTs can be…
Orthodromic or Antidromic
AVRT result from….
An accessory pathway
ECG features of an orthodromic AVRT
200-300bpm
P waves buried in QRS
T wave inversion
ST depression
ECG features of an antidromic AVRT
200-300bpm
Wide QRS
Bundle of Kent
Accessory pathway seen in Wolff-Parkinson White syndrome
Wolff-Parkinson-White Syndrome
AVRT resulting from a specific accessory pathway - the Bundle of Kent
ECG features seen in Wolff-Parkinson-White Syndrome
PR interval <120ms
Delta wave
QRS prolongation
ST segment and T wave changes
Delta Wave
Slurring, slow rise of initial portion of QRS
Seen in WPW Syndrome
Peri-infarct zone consists of…
Dense scar tissue dispersed between living, normal cells
How does scar tissue cause reentry tachycardia?
Flow of impulse perpendicular to line of muscle cells is much slower than usual.
When excitation reaches the end of the muscle cells, it is able to stimulate them perpendicularly in the opposite direction (since it is not in ERP)
Triggered Activity
Impulse initiation in cardiac fibres that is dependent on after depolarisations
After-depolarsations
Oscillations in membrane potential that follow the upstroke of an action potential.
Causes of repolarisation abnormalities (3)
Drugs
Genetic predisposition
Electrolyte imbalance
Why do cardiac cells have automaticity?
They can generate spontaneous action potentials due to diastolic depolarisation.
i.e. net inward current during phase 4 of action potential
Broad complex tachycardia
QRS complex >120ms
Narrow complex tachycardia
QRS complex <120ms
Causes of broad complex tachycardia
VT
SVT + BBB
Accessory pathway related
Causes of narrow complex tachycardia
Atrial fibrillation Atrial flutter Multifocal Atrial tachycardia AVNRT/AVRT (short PR) Sinus tachy/Atrial tachy (long PR)
Tachycardia
> 100bpm
Sinus rhythm
P wave before every QRS complex
Normal PR interval (120-200ms)
Regular rhythm
Normal PR interval
120-200ms
Sinus Arrhythmia
Normal phenomenon in the young
Heart rate increases when a deep breath is taken in and out
Symptoms of arrhythmias
Palpitations Dyspnoea Presyncope (dizziness) Chest pain Sudden cardiac death
Since palpitations are a common symptom, you should also ask about (the palpitations)…
Duration
Onset
Associated symptoms
Why do arrhythmias cause dyspnoea?
Reduced cardiac output
Why do arrhythmias cause chest pain?
O2 demand exceeds supply.
Demand may be high due to tachycardia
Supply may be low due to low cardiac output
Why do arrhythmias cause presyncope?
Inadequate cerebral perfusion
Prevalence of sudden cardiac death
1/1000 per year
Arrhythmias causing sudden cardiac death
Ventricular fibrillation
Polymorphic ventricular tachycardia
Monomorphic ventricular tachycardia
Proportion of sudden cardiac deaths with structurally abnormal heart
2/3
Proportion of sudden cardiac deaths resulting from coronary artery disease
80%
On an ECG, Ventricular ectopic beats…
Broad QRS
On an ECG, Atrial ectopic beats…
Narrow QRS
Inverted P waves
Compensatory pause afterwards
Paroxysmal AF
Episodes last <48hrs
Persistent AF
Episodes last 48hrs-1 week
Permanent AF
Symptoms occurring at all times
Structural heart disease causing AF
Valvular, Ischaemic, Hypertensive and congenital heart disease
Athletes heart
Cardiomyopathies
Causes of AF with no structural heart disease
Metabolic e.g. hyperthyroidism
Biochemical e.g. Hyperkalaemia
Drugs e.g. caffeine, alcohol
Severe infections
MOA of flecainide
VW Class Ic - Na+ channel blocker
MOA of Propafenone
VW Class Ic - Na+ channel blocker
MOA of amiodarone
VW Class III - K+ channel blocker
MOA of dronedarone
VW Class III - K+ channel blocker
First degree heart block
Prolonged PR interval (<200ms)
Second degree heart block
Occasionally a P wave does not elicit a QRS complex
Mobitz Type I Heart Block
PR interval gets longer until eventually, P wave fails to elicit a QRS complex
Mobitz Type II Heart Block
PR interval stays the same.
Occasionally, a P wave does not elicit a QRS complex
2:1 Heart Block
Every 2nd P wave does not elicit QRS
3:1 Heart Block
Every 3rd P wave does not elicit a QRS
Complete Heart block
Complete AV dissociation
Causes of Heart Block
Age-related Acute ischaemia Hyperkalaemia Hypothermia Hypothyroidism Drugs (AVN blockers) Congenital Raised ICP
Management of heart block
Permanent Pacemaker
Brugada syndrome
ECG shows ST elevation
Leading cause of sudden cardiac death in young males
As a cardioaccelerator, Noradrenaline acts principally on…
Sinoatrial Node
As a cardioinhibitor, Acetylcholine acts principally on…
Atrioventricular Node
Indication for VW Class I
SVT, AVNRT, WPW
VW Class I
Na+ channel blockers
VW Class IA
Moderate Na+ channel blockers
Increase ERP
VW Class IB
Weak Na+ channel blockers
Decrease ERP
VW Class IC
Strong Na+ channel blockers
No effect on ERP
VW Class IA Example
Procainamide
VW Class IB Example
Lidocaine
VW Class IC Example
Flecainide
ADRs of Lidocaine in treatment of arrhythmias
Dizziness
Paraesthesia
Drowsiness
Bradycardia
ADRs of Flecainide
Oedema Dyspnoea Dizziness Fever Visual Disturbance
Contraindications of Lidocaine
AV block
Myocardial depression
Contraindications of flecainide
Heart failure
History of MI
heart block
Indication for lidocaine (Class IB)
Ventricular tachycardias
Indication for flecainide (Class IC)
For life threatening SVT and VT
Indication for VW Class IA
AF
A.Flutter
SVT
VT
VW Class II
Beta 1 Adrenoceptor Antagonists
MOA of Bisoprolol
Beta 1 Adrenoceptor Antagonist
Indication for bisoprolol
SVT
ADRs of bisoprolol
Hypotension Cardiac failure Bronchospasm Bradycardia Cold Extremities Loss of libido Sleep disturbance
Contraindications of Bisoprolol
COPD/Asthmatic In cardiogenic shock Bradycardia Cardiac failure AV block
Why should beta-blockers be used cautiously in patients with diabetes?
The drug will mask the warning sign (tachycardia) for insulin-induced hypoglycaemia
VW Class III
K+ channel blockers
VW Class III Example
Amiodarone
Indications for VW Class III
VT, AF, WPW, Atrial Flutter
Tachyarrhythmias caused by reentry
ADRs of Amiodarone
Torsade de Pointes (esp. in those with LQT) Bradycardia AV Block Grey skin abnormalities Phototoxicity Liver failure Pulmonary fibrosis Sleep disorders Tremor Thyroid abnormalities
Indications for Amiodarone
VT, AF, WPW, Atrial Flutter
Tachyarrhythmias caused by reentry
Contraindications of Amiodarone
Heart block
SAN dysfunction
Iodine sensitive
Existing thyroid dysfunction
VW Class IV
Ca2+ channel blockers
VW Class IV Examples
Verapamil
Diltiazem
Indications for VW Class IV
Paroxysmal SVT
AF (reduces ventricular rate)
Hypertension
ADRs of verapamil
Dyspnoea Constipation Arrhythmia Tachycardia Hypotension Headache Ankle oedema
Contraindications of Verapamil
Hypotension Bradycardia AV Block (2nd and 3rd) Cardiogenic shock Heart failure WPW
VW Class V
Adenosine
Indication for Adenosine
AVNRT
WPW
MOA of Adenosine
Binds to A1 receptor Inhibits Adenylyl Cyclase Decreased cAMP Hyperpolarisation due to K+ traffic Inhibits Ca2+ entry
ADRs of adenosine
Flushing
headache
Rapid arterial hypotension
AV Block
Contraindications of Adenosine
AV Block (2nd or 3rd)
Why is rate control usually trialled first?
Fewer ADRs
Safer for patients
CHADS2VASC
Congestive Heart Failure/LV dysfunction (1)
Hypertension (1)
Age > 75 (2)
Diabetes Mellitus (1)
Stroke/Thromboembolism (2)
Vascular Disease (1)
Age 64-75 (1)
Sex (female) (1)
Administration of Warfarin
Oral
MOA of Warfarin
Vitamin K Carboxylase inhibitor
Clotting factor synthesis inhibited by Warfarin
VII, IX, X
Monitoring for warfarin
Regular measurement of Prothrombin Time to determine INR
Normal INR
<1.1
Target INR for those taking anticoagulants
2-3
Antedote for Warfarin
Vitamin K
Administration of Heparin
IV
MOA of heparin
Activates anti-thrombin III which inactivates thrombin and Factor Xa
MOA of Fondaparinux
LMWH
Inhibits Factor Xa only
Monitoring of Heparin
Regular measurement of prothrombin time against activated partial thromboplastin time (aPTT)
Antedote for Heparin
Protamine Sulphate
MOA of Dabigatran
Thrombin Inhibitor
MOA of Rivaroxaban
Factor X inhibitor
MOA of Apixaban
Factor X inhibitor
Synergism of warfarin and heparin causes…
Penile Necrosis
Fundoscopy for hypertensive crisis shows…
Cotton wool spots
Flame haemorrhages
Papilloedema
Urinalysis in hypertension shows..
Increased albumin:creatinine ratio
ACR
Important blood tests in investigating hypertension
Plasma glucose Electrolyes Creatinine Estimated GFR Serum total cholesterol HDL cholesterol
Prohypertensive proteins
Angiotensinogen
Renal epithelial Na+ channels
Adrenoceptors found on the surface of blood vessels
Alpha 1 and 2
Function of Renin
Converts Angiotensinogen to Angiotensin I
Function of ACE
Converts Angiotensin I to Angiotensin II
Who is offered treatment for hypertension?
Stage 1, >80yo with one or more of the following: Target organ damage Diabetes CVD Renal disease 10yr risk of CVD >20%
All patients with stage 2 hypertension
Initial treatment for patients under 55, not of African/Caribbean origin
With Hypertension
- ACE inhibitors
If not tolerated:
- ARB
Initial treatment for patients over 55, or of African/Caribbean origin with Hypertension
- CCBs
If CCB causes oedema or there is evidence of heart failure:
- Thiazide-like diuretic
If step 1 is ineffective, step 2 anti-hypertensive treatment is…
CCB/Thiazide-like diuretic + ACE/ARB
ARB>ACE for African/Caribbean origin
If step 2 is ineffective, step 3 anti-hypertensive treatment is…
ACE/ARB + CCB + Thiazide-like diuretic
If step 3 is ineffective, step 4 anti-hypertensive treatment is…
Addition of low dose spironolactone if K+<4.5mmol/L
OR
Increase dose of thiazide-like diuretic if K+>4.5mmol/L
MOA of Ramipril
ACE inhibitor
Method of BP reduction by ramipril
Blocks Na+ reuptake in kidneys (and therefore water reuptake)
Limits LV remodelling
Reduces vasomotor tone (since there is less angiotensin II)
Contraindications of ACE inhibitors
Hypersensitivity to ACE inhibitors
Renovascular disease
ADRs of ACE inhibitors
Hypotension Renal impairment Persistent dry cough angioedema Rash
Method of BP reduction by Losartan
Blocks Na+ reuptake in kidneys (and therefore water reuptake)
Limits LV remodelling
Reduces vasomotor tone (since there is less angiotensin II bound to its receptor)
MOA of Losartan
ARB
ARBs should be used with caution in patients with…
Renal artery stenosis
Aortic/Mitral valve stenosis
ADRs of ARBs
Hypotension - dizziness
Hyperkalaemia (occasionally)
Angioedema (rare)
Method of BP reduction by CCBs
Negative chronotrope and inotrope
Prevents vascular smooth muscle cell contraction
MOA of Nifedipine
CCB
MOA of Isradipine
CCB
Contraindications of CCBs
Cardiogenic shock
Aortic stenosis
Recent MI (within 1 month)
Acute/Unstable Angina
ADRs of CCBs
GI disturbance Oedema Palpitations Headache Lethargy Dizziness
MOA of Furosamide
Blocks Na/K/Cl reabsorption in loop of Henle
Loop diuretic
Contraindications of Furosamide
Hypokalaemia
Hyponatraemia
Renal failure
Comatose associated with liver cirrhosis
ADRs of furosamide
GI disturbance
Increased serum cholesterol
Electrolyte disturbance
Hyperglycaemia
MOA of Bendroflumethiazide
Blocks Na/Cl absorption in DCT
Thiazide diuretic
Contraindications of bendroflumethiazide
Hypokalaemia Hyponatraemia Hypocalcaemia Hyperuricaemia (high uric acid in blood) Addison's Disease
ADRs of bendroflumethiazide
GI disturbance
Electrolyte disturbance
Hyperglycaemia
MOA of Spironolactone
Blocks aldosterone receptor in collecting duct. Blocking Na+ reabsorption but K+ sparing.
Contraindications of spironolactone
Hyperkalaemia
Anuria
Addison’s Disease
ADRs of Spironolactone
GI disturbance Gynaecomastia Breast pain Menstrual disturbance Drowsiness/Dizziness Hyperkalaemia Hyponatraemia
Advantages of ARBs over ACE inhibitors?
ARBs do not prevent production of angiotensin II altogether
So angiotensin II can still exert its effects in other areas of the body.
ARB does not cause cough.
Method of BP reduction by bisoprolol
Inhibition of renin release
Negative chronotrope and inotrope
Method of BP reduction by GTN spray
Releases NO causing vasodilation
How does NO cause vasodilation?
Activation of guanylyl cyclase. Increased cGMP Causing: Increased K+ efflux Decreased Ca2+ influx Increased MLC phosphatase
Rhythm Strip
Prolonged reading from a single lead (usually lead II)
Useful for analysis of heart rate and rhythm
aVR is predominantly…
Negative
T wave inversion is normal in…
aVR and V1
Children
Sinus Rhythm
Regular rhythm
P waves followed by QRS complexes
Normal PR interval (120-200ms)
Enlargement of Right Atrium
ECG shows…
Tall pointed P waves
Enlarged left atrium
ECG shows…
Bifid P waves
P-mitrale
Bifid P waves due to enlarged Left Atrium
Right ventricular hypertrophy
ECG shows…
Taller R waves in V1 (R:S >1)
Deeper S waves in V5 or V6 (R:S <1)
Deep, broad Q waves indicate…
Permanent myocardial damage from MI
Permanent myocardial damage from an inferior MI
ECG shows…
Deep, broad Q waves in II, III and aVF
Right bundle branch block
ECG shows…
Prolonged QRS (>120ms)
Tall R wave in V1 (M)
Wide, slurred S wave in V6 (W)
MaRRoW
Left bundle branch block
ECG shows…
Prolonged QRS (>120ms)
Dominant S wave in V1 (W)
Notched R wave in V6 (M)
WiLLiaM
Cardiac ischaemia
ECG shows…
ST depression in associated leads
Anterior Myocardial Infarction
ECG shows…
ST elevation in V1-V6
Septal MI
ECG shows…
ST elevation in V1-V4
Lateral MI
ECG shows…
ST elevation in I, aVL, V5 and V6
Inferior MI
ECG shows…
St elevation in II, III and aVF
Anterior MI is due to infarction in which coronary artery?
LAD
Septal MI is due to infarction in which coronary artery?
LAD
Lateral MI is due to infarction in which coronary artery?
Left circumflex
Inferior MI is due to infarction in which coronary artery?
RCA (80%) Left Circumflex (20%)
Hyperkalaemia
ECG shows…
Tall T waves
Pathological inverted T waves:
Raised ICP BBB Ventricular HTN PE Hypertrophic Cardiomyopathy MI or ischaemia
Normal PR interal
120-200ms
Normal QRS complex
80-100ms
Normal RR interval
0.6-1.2s
ECG - 1 square =
0.04s/0.1mV
Management of MI
Primary Percutaneous Intervention
Heart rhythm abnormalities associated with MI
Atrial fibrillation
Complete heart block
VT
VF (Arrest)
Long QT syndrome
ECG shows…
T wave flattening
Prominent U waves
Long QT interval due to fusion of T and U waves
Rhythm abnormality associated with LQT syndrome
Torsade de Pointes (Polymorphic VT)
Main causes of LQT syndrome (3)
Drugs
Myocardial Ischaemia
Electrolyte imbalance (esp. Hypokalaemia)
Wolff Parkinson White Syndrome
ECG shows…
Delta waves
Short PR interval
Broad QRS complex
Rhythm abnormalities associated with WPW
AF
Narrow complex tachycardia
VF
Patient with AF has there AVN ablated and a pacemaker implanted.
What drug treatment must they continue?
Anticoagulants - since atria are still fibrillating so there is no change in stroke risk.
Rhythm control treatments:
Class Ic
Class III
DC Cardioversion
PVI
Rate control treatment:
Class II
Class IV
Pace and Ablate
Primary prevention ICD
When cardiac arrest risk is proportional to scar burden.
Prior MI and EF <30%
Secondary prevention ICD
Life threatening cardiac episode:
Cardiac arrest with no obvious reversible cause
Syncopal VT and structural Heart Disease
Non syncopal VT and EF<35%
Management of Atrial Fibrillation
Beta blocker or CCB
Ineffective?
Beta blocker and CCB (or digoxin if sedentary)
Ineffective?
Rhythm control - VW Ic or III or DC cardioversion
Management of Atrial flutter
Beta blocker OR Diltiazem (CCB) or Verapamil (CCB)
Ineffective?
Add digoxin
Management of Ventricular Tachycardia
DC cardioversion
OR Amiodarone and DC cardioversion
Management of Wolff-Parkinson White
Amiodarone
Flecainide (VW Ic)
Ablation of accessory pathway.