Arrhythmias: Bradycardia, Heart block, and Bundle branch block Flashcards Preview

Cardio-Resp > Arrhythmias: Bradycardia, Heart block, and Bundle branch block > Flashcards

Flashcards in Arrhythmias: Bradycardia, Heart block, and Bundle branch block Deck (28)
Loading flashcards...

What are the two main types of arrhythmia?

Bradycardia <60bpm
Tachycardia >100bpm


Outline the complications of arrhythmias

Chest pain
Heart failure
Sudden death


Describe the function of the Sinoatrial node

A spindle-shaped structure located in the junction between the SVC and RA.

It is the natural cardiac pacemaker that automatically spontaneously depolarises, faster than other pacemaker cells. This initiates the electrical impulse that results in contraction of myocytes. The rate at which the SAN fires determines the heart rate.


Describe the sinoatrial node action potential

1. HCN Na channels open, allowing slow depolarisation (known as the funny current)
2. Upon reaching threshold, L-type Ca channels open, producing an action potential
3. VG K channels open, allowing repolarisation


Explain the mechanisms of arrhythmia production

Accelerated automaticity: an area of myocardial cells depolarises faster than the SAN

Triggered activity: myocardial damage release electrical activity (after-depolarisations), that can reach threshold and produce an arrhythmia.

Re-entry: propagating AP travels retrograde to form a re-entry loop, which repeatedly excites the myocardium. This produces the majority of regular paroxysmal tachycardias.


Explain how the different types of bradycardia occur

Sinus bradycardia: failure of impulse formation

AV block: failure of impulse conduction from the atria to
the ventricles.


Name 4 causes of sinus bradycardia

Extrinsic factors:
-Hypothermia, hypothyroidism
-Cholestatic jaundice
-Raised intracranial pressure
-Drugs: Beta-blockers and other antiarrhythmics
-Neurally mediated syndromes: carotid sinus syndrome, vasovagal syncope, postural tachycardia syndrome

Intrinsic sinus node disease:
-Acute ischaemia and infarction of sinus node
-Chronic degeneration: fibrosis, sick sinus syndrome
-Infilitrative disease: sarcoidosis, haemochromatosis


Define normal sinus rhythm

Pacemaker impulses arise from sinoatrial node
Regular rhythm at 60-100 bpm
Each QRS complex is preceded by a normal P wave
PR interval is constant
Narrow-complex QRS (<100 ms)


Define sick sinus syndrome

Abnormal sinus node function with resultant bradycardia and cardiac insufficiency


Define Carotid sinus syndrome

Bradycardia and syncope due to an exaggerated response to carotid sinus baroreceptor stimulation.
Occurs when rotating head.


Define Vasovagal syncope

Syncope resulting from autonomic failure due to physical and/or emotional stress. Causes bradycardia and/or vasodilation.


Define Postural tachycardia syndrome

Abnormal sudden and significant increases in heart rate produced by sitting or standing up. Failure of peripheral vasoconstriction causes dizziness and syncope.


What is the management of vasovagal syncope?

Avoidance of known triggers
Avoid prolonged upright position
Sitting/lying down and applying counter-pressure (pushing palms together, crossing legs) if attack occurs

Increased salt intake, compression hosiery

Disopyramide (negative inotrope)


Differentiate the types of heart block

First-degree: PR interval prolongation (>220ms). All atrial activity is conducted to the ventricles.

Second-degree: Some P waves conduct, others don't.
-Mobitz I: Progressive prolongation of PR interval, until a P wave fails to conduct.
-Mobitz II: Spontaneous dropping of QRS without progressive PR prolongation (usually wide >120ms).
-2:1 or 3:1 block: Every 2nd/3rd P wave conducts.

Third-degree: All atrial activity fails to conduct to the ventricles.


Describe the pathophysiology of third-degree heart block

All atrial activity fails to conduct to the ventricles. Slower pacemaker cells become responsible for initiating ventricular contract to sustain life. These are known as spontaneous escape rhythms, and may be narrow- (originating from bundle of His) or broad-complex (originating from ventricular pacemakers).


Define narrow-complex escape rhythms in third-degree heart block

Spontaneous electrical impulses originating in the bundle of His, which produce a QRS complex <120ms. This escape rhythm occurs at 50-60 bpm.

Region of AV block lies more proximal in the AV node.


Outline the management of narrow-complex escape rhythms in third-degree heart block

Atropine up to 3mg
Temporary transcutaneous pacing


Define broad-complex escape rhythms in third-degree heart block

Spontaneous electrical impulses originating from ventricular pacemaker cells, which produce a QRS complex >120ms. This escape rhythm occurs at 15-40 bpm.

Region of AV block lies more distal in the His-Purkinje system.

Adams-Stokes syndrome: Dizziness and loss of consciousnesses often occur


Outline the management of broad-complex escape rhythms in third-degree heart block

Permanent transvenous pacemaker is indicated

If pacemaker is delayed:
Atropine, up to maximum of 3mg
Temporary transcutaneous pacing
Adrenaline infusion: titrated to response


List 5 causes of third-degree heart block

Congenital: Maternal SLE, Structural heart disease
Idiopathic fibrosis: Lev's disease, Lenegre's disease
IHD: Acute MI, Ischaemic cardiomyopathy
Non-IHD: Calcific aortic stenosis, idiopathic dilated cardiomyopathy, infiltrations (sarcoid, amyloid, cancer)
Cardiac surgery
Iatrogenic: Radiofrequency AVN ablation, pacemaker
Drug: Digoxin, beta-blocks, non-dihydropyridine CCB
Infections: Endocarditis, Lyme disease, Chagas disease
Rheum: SLE, RA
NMD: Duchenne muscular dystrophy


Describe the anatomy of the bundle of His

The bundle of His starts from the AVN, and travels down the interventricular septum.
It divides into the main left bundle branch and right bundle branch.
The main LBB divides into an anterior-superior division and a posterior-inferior division.


Describe the ECG of complete bundle branch block

Associated with wide QRS (>120ms)

RBBB: Deep S wave in I and V6, Tall late R wave in V1
LBBB: Deep S wave in V1, Tall late R wave in I and V6


Describe the ECG of bundle branch conduction delay

Slight widening of QRS (up to 110ms)
Known as incomplete BBB


What is hemiblock?

Delay or block in one of the divisions of the LBB.
-Left anterior hemiblock: causes left axis deviation
-Left posterior hemiblock: causes right axis deviation


Define Bifascicular block

Combination delay or block of any two of following:
-Right bundle branch
-Left anterior-superior fascicle
-Left posterior-inferior fascicle


Define Trifascicular block

Combination delay or block in all three:
-Right bundle branch
-Left anterior-superior fascicle
-Left poster-inferior fascicle


What ECG changes are seen in incomplete and complete trifascicular block?

Incomplete: RBBB + LAD + First-degree AV block
Complete: RBBB + LAD + Third-degree AV block


What ECG changes are seen in bifascicular block?