Arrhythmias Pathophysiology, Presentation and Investigation Flashcards
What is sinus rhythm?
Sinus rhythm is a normal heart beat, with respect to both the heart rate and rhythm
Normal heart rate is between 60 and 100 beats per minute
What is atrioventricular block influenced by?
Autonomic activity
What are the features of first degree atrioventricular block?
AV conduction is delayed, so PR interval is prolonged (> 20 secs)
What are the features of second degree atrioventricular block?
Dropped beats occur because some impulses from the atria fail to conduct to the ventricles
What are the features of Mobitz type I second degree AV block?
Progressive lengthening of successive PR intervals culminating in a dropped beat
What are the features of Mobitz type II second degree AV block?
PR interval remains constant but some P waves are not conducted
What are the features of third degree (complete) atrioventricular block?
AV conduction fails completely resulting in the atria and ventricles beating independently
Ventricular activity is maintained by an escape rhythm arising in the AV node or Bundle of His (narrow QRS complexes) or the distal Purkinje tissues (broad QRS complexes)
What is the pulse and SV in third degree AV block?
Slow pulse, 25-50bpm, large volume, that does not vary with exercise
Increased stroke volume
What murmurs can be heart in third degree AV block?
Systolic flow murmurs
What is the management of second and third degree atrioventricular block?
Second degree or complete may respond to atropine or temporary pacemaker
What is the management of second degree or complete heart block which is complicating an acute MI?
Requires a temporary pacemaker
What is the management of atrioventricular block with systole?
IV atropine or isoprenaline to maintain circulation until pacemaker is inserted
What is the management of chronic atrioventricular block?
Permanent pacemaker
What is atrial flutter characterised by?
Large re-entry circuit within the right atrium, usually encircling the tricuspid annulus
What is the atrial rate in atrial flutter?
Approximately 300/min
What is atrial flutter usually associated with?
Atrioventricular block
When should atrial flutter be suspected?
Where there is a narrow complex tachycardia of 150/min
How might carotid sinus massage or IV adenosine help establish a diagnosis of atrial flutter?
By temporarily increasing the degree of AV block and revealing the flutter waves
What is the most common sustained cardiac arrhythmia?
Atrial fibrillation
What is atrial fibrillation characterised by?
The presence of multiple, interacting re-entry circuits looping around the atria
What are episodes of atrial fibrillation initiated by?
Salvoes of ectopic beats that can arise from conducting tissue in the pulmonary veins or from diseased atrial tissue
What is the pulse in atrial fibrillation?
Irregularly irregular
What is the ECG like in atrial fibrillation?
Irregular QRS complexes with no P waves
What are the types of atrial fibrillation?
Paroxysmal
Persistent
Permanent
When is atrial fibrillation more likely to become sustained?
In enlarged atria with slow conduction
What is the presentation of atrial fibrillation?
Palpitations
Dyspnoea
Fatigue
May precipitate or aggravate cardiac failure
Light-headedness if hypotension
Chest pain if underlying coronary disease
Often asymptomatic and detected accidentally
What is the management of atrial fibrillation?
Full history and examination 12 lead ECG - document arrhythmia Echocardiogram Thyroid function Exercise tolerance test Treat any underlying primary disorder e.g. if complicating an acute illness Beta blockers CCBs for rate control Anticoagulation if stroke/emboli risk
What is supraventricular tachycardia?
Supraventricular tachycardia is used to describe a range of regular tachycardias that have a similar appearance on an ECG
These tachycardias are usually associated with a narrow QRS complex and are characterised by a re-entry circuit or automatic focus involving the atria
What are the features of AV nodal re-entrant tachycardia?
Palpitations Dyspnoea Dizziness Good prognosis No treatment Narrow QRS complex
What is the management of supraventricular tachycardia?
CCBs e.g. verapamil/diltiazem for paroxysmal SVT
CCBS and beta-blockers e.g. atenolol, bisoprolol for frequent or disabling SVT
Describe Wolff-Parkison-White Syndrome
In Wolff-Parkinson-White syndrome there is a strip of accessory conducting tissue that allows electricity to bypass the AV node and spread from the atria to the ventricles rapidly and without the delay
When the ventricles are depolarised through the AV node, the ECG is normal, but when the ventricles are depolarised through the accessory conducting tissue the ECG shows a very short PR interval and a broad QRS complex
When is ventricular tachycardia most commonly seen?
In patients with CHD or cardiomyopathies
Why is ventricular tachycardia serious in patients with CHD or cardiomyopathies?
It can lead to haemodynamic compromise or ventricular fibrillation
What is the presentation of ventricular tachycardia?
Palpitations Chest pain Dyspnoea Dizziness Syncope
What is the management of ventricular tachycardia?
Fast sodium channel blockers e.g. quinidine
Intermediate sodium channel blockers e.g. phenytoin
Slow sodium channel blockers (only in severe dysrhythmias) e.g. flecainide
Beta blockers e.g. atenolol for myocardial depression
Amiodarone, sotalol or bretylium if sustained/life threatening
Implantable cardioverter defibrillator
What is the presentation and management of ventricular fibrillation?
Presents with collapse and sudden cardiac arrest
Cardiac arrest protocol to be followed
What is sinus tachycardia?
Defined as a sinus rate of more than 100/min and is usually due to an increase in sympathetic activity associated with exercise, emotion, pregnancy or pathology
In what people can a rapid sinus rate be normal?
In young adults with intense exercise
In what people can a sinus rate of less than 60/min be normal?
In healthy people at rest e.g. in athletes
What are some pathological causes of sinus bradycardia?
MI Sinus node disease Hypothermia Hypothyroidism Drugs
What is the treatment of sinus bradycardia?
No treatment if asymptomatic
Symptomatic usually responds to IV atropine
What is sinus arrest?
A condition wherein the sinoatrial node of the heart transiently ceases to generate the electrical impulses that normally stimulate the myocardial tissues to contract and thus the heart to beat
What is the presentation of atrial ectopic beats?
Usually asymptomatic but can give the sensation of a missed or abnormally strong beat
What does the ECG show in atrial ectopic beats?
Shows premature but otherwise normal QRS complex
If visible, the preceding P wave has a different morphology because the atria activate from an abnormal site
What might atrial ectopic beats precede, if occurring frequently?
Onset of atrial fibrillation
What does the ECG show in ventricular ectopic beats?
QRS complexes are of abnormal morphology because the bundle branches are activated one after the other, rather than simultaneously
The ECG shows premature broad complexes which may be unifocal or multifocal
What effect do ventricular ectopic beats have on the stroke volume?
Ectopic beats produce a low stroke volume because left ventricular contraction occurs before filling is complete
What is the pulse in ventricular ectopic beats?
Pulse is irregular, with weak or missed beats, or abnormally strong beats
What does the significance of ventricular ectopic beats depend on?
Presence or absence of underlying heart disease
What are the indications for ICD therapy?
Secondary prevention
Cardiac arrest due to VF/VT not due to transient or reversible cause e.g. early phase of acute MI
Sustained VT causing syncope or significant compromise
Sustained VT with poor LV function
What are the indications for temporary pacing?
Intermittent or sustained symptomatic bradycardia, particularly syncope
Prophylactic when a patient is at high risk for development of severe bradycardia e.g. 2nd or 3rd degree AV block, post-anterior MI, even when asymptomatic
What are the indications for permanent pacing?
Symptomatic or profound 2nd/3rd degree AV block, particularly when cause is unlikely to disappear
Probably Mobitz type II 2nd and 3rd degree AV block, even if asymptomatic
AV block associated with neuromuscular diseases
After, or in preparation for, AV node ablation
Alternating right bundle branch block/left bundle branch block
Syncope when bifascicular/trifascicular block and no other explanation
Sinus node disease associated with symptoms
Carotid sinus hypersensitivity/malignant vasovagal syncope
