ELFH - cardiac arrhythmias Flashcards
What node is the cardiac pacemenaker?
SA node
How doe the SA node and AV node cause contraction of the heart?
It initiates the impulse and thereby determines the heart rate. Once initiated, the impulse is distributed throughout the atrial muscle fibres to cause synchronous atrial contraction.
Distribution of the electrical impulse to the ventricular muscle is momentarily delayed at the atrioventricular (AV) node (Figure 3). This enables the atria to contract and pump blood into the ventricles before ventricular contraction is initiated.
From the AV node, the electrical impulse then spreads throughout the ventricular muscle. It 1st passes down the AV bundle (Figure 4), then down the right and left bundle branches to supply the right and left ventricles, respectively (Figure 5). Finally it reaches the Purkinje fibres (Figure 6). This conducting system ensures synchronous and powerful ventricular contraction.
What is an ECG?
trans-thoracic interpretation of the electrical activity of the underlying heart muscle.
What type of ECG can show significant info about the heart?
12-lead
What does a 12-lead ECH show?
shows the heart rate and rhythm, and can provide information about the heart’s size and structure.
Can an ECG recognise damage to the heart?
yes,
can help recognise damage to the heart, such as during a heart attack, and can help diagnose abnormal rhythms.
What does the PR interval show?
The PR interval is the interval between a P wave and the upstroke of a QRS complex. This represents the passage of electrical current between the atria and ventricles.
What does the P wave show?
The P wave represents atrial contraction.
What does the QRS wave show?
The QRS complex represents ventricular contraction
What does the T wave show?
The T wave represents ventricular relaxation
When do cardiac arrhythmias occur?
when there is an abnormality within the cardiac conducting system
How might cardiac arrhythmias manifest clinically?
dizziness, fatigue, palpitations, collapse, shortness of breath or sudden cardiac death. There may be no symptoms at all.
Broadly, what do cardiac arrhythmias divide into?
bradycardias (heart rate <60 beats per min)
tachycardias (heart rate >100 beats per min)
heart rate for bradycardia? `
under 60 beats per min
heart rate for tachycardia?
over 100 beats per min
What do you call normal HR rhythm?
sinus rhythm
Where the heart rate is slow or fast but has a normal rhythm
e.g during exercise
Who would have sinus bradycardia?
athletes
patients with hypothermia
hypothyroidism
Who would have sinus tachycardia?
experienced during exercise
seen with fever
hyperthyroidism
What is a common cause of cardiac arrhythmias?
AF
Why does AF occur?
when electrical activity within the atria becomes disordered and chaotic (Figure 1).
Consequently, the muscle fibres of the atria no longer contract in synchrony; instead they ‘fibrillate’ making the atria mechanically ineffective.
In AF, how frequently do atrial muscle fibres fire?
300-600 beats per min
In AF do all of the electrical impulses fire the AV node?
no
manifest as irregular pulse
How does AF look on an ECG?
Lack of P wave
and by an irregular ventricular rate
What is the venbtricular rate in AF?
120 to 180 per min
compared to atrial muscles firing at around 300-600 BPM
What are conditions which could cause AF?
most common cause IHD
Rheumatic heart disease is also an important cause, although is becoming less prevalent. Longstanding hypertension, mitral valve disease and cardiomyopathy are other important causes of AF.
any condition which structurally alters the atria
can also be idiopathic
When does AF occur?
when there is continuous, rapid activation of the atria secondary to ectopic electrical discharge within the atria.
What are causes of AF precipitated by systemic events?
alcohol toxicity, pneumonia and hyperthyroidism. This may occur in a structurally normal heart.
What is idiopathic AF known as?
lone AF
3 approaches to managing AF?
RHYTHM CONTROL
RATE CONTROL
STROKE PREVENTION
Rhythm control as a management technique for AF?
In patients with new onset AF, or with adverse symptoms and signs, it may be appropriate to attempt to restore normal sinus rhythm. This is termed ‘cardioversion’ and may be attempted with a synchronised DC shock or chemically with anti-arrhythmic drugs such as amiodarone or flecainide.
Rate control as a management technique for AF?
Fast AF can compromise cardiac output and cause insufficient tissue oxygenation. Rate control is achieved by drugs that block the AV node.
The aim is to keep the ventricular rate <90 per min. Agents commonly used include beta blockers (for example, bisoprolol) and digoxin. Rate control alone does not correct the abnormal rhythm.
Stroke prevention as a management technique for AF?
his is achieved with anticoagulation and depends on the patient’s stroke risk. It is usually achieved with warfarin with a target international normalised ratio (INR) of 2 to 3.
Dentists will be increasingly exposed to newer oral anticoagulants such as rivaroxaban, apixaban and dabigatran. The management of these patients in dental practice are covered by guidelines, for example, the Scottish Dental Clinical Effectiveness Programme (SCDEP).
What INR score should no dental tx be carried out?
over 4.0 (SDCEP)
If the an INR score above 4.0 cannot be achieved what do you do (dental tx)?
may have to be carried out in a secondary care environment
If a pt is on warfarin, what do you need to do before carrying out any dental procedure?
the patient’s INR must be obtained prior to any invasive procedures, ideally on the day of the procedure.
If warfarin is taken. what are alterative which can be taken in order to carry out the dental procedure safely?
anti-fibrinolytic tranexamic acid mouth rinses, may need to be considered
Risk of adrenaline and AF pt?
the risk of direct intravascular injection and subsequent dysrhythmias, is very small
What percentage of people aged over 65 have AF?
5-10%
When does heart block occur?
when there is a delay in the conduction of electrical current as it passes through the cardiac conduction system (Figure 1).
Symptoms of heart block?
Symptoms vary according to the site of the delay.
Many patients are symptom-free.
In others, symptoms include:
- fatigue, dizziness and collapse.
Heart block can also present as a medical emergency.
What are the 2 categories of hart block?
atrioventricular block
bundle branch block
bundle branch block?
occurs when there is an abnormality lower down in the conducting system
atrioventricular block?
occurs when there is block at the level of the AV node
When does first degree heart block occur?
when there is delayed electrical conduction to the ventricles following atrial activation.
However, every impulse reaches the ventricles. It is relatively common and rarely causes symptoms.
How does first degree heart block appear on an ECG?
first degree heart block causes a prolonged P-R interval
When does second degree heart block occur?
when there is intermittent block of impulses to the ventricles.
The heart may beat slowly, irregularly or both
What are the 2 subdivision of second degree heart block?
‘Wenckebach’ or Mobitz type 1 block (Figure 1)
Mobitz type 2 block (Figure 2)
Wenckebach’ or Mobitz type 1 block?
‘Wenckebach’ or Mobitz type 1 second degree heart block. In this ECG, the P-R interval gets progressively longer with each cardiac cycle until a QRS complex is missed
Another name for third degree heart block?
complete heart block
When does third degree heart block occur?
when there is complete failure of conduction to the ventricles from the atria.
Life is maintained by so called ‘escape rhythms’ generated in conducting tissue within or distal to the AV node.
This results in a very slow heart rate (<50 beats per min).
Is third degree heart block a serious condition?
yes
adversely affect heart function
symptoms of third degree heart block?
dizziness, fainting and fatigue.
How does third degree heart block appear on an ECG?
There is no relationship between P waves and QRS complexes and the ventricular rate is slow.
Who is likely to have first degree heart block? (causes)
often seen in athletes and young patients.
It is also seen in structural heart disorders such as rheumatic heart disease.
It may also be caused by drugs.
Who is likely to have second degree heart block? (causes)
some young people and athletes.
Second degree heart block may also be seen with structural abnormalities of the heart.
An important cause in all types of second degree heart block is acute myocardial infarction.
Who is likely to have third degree heart block? (causes)
In older people, it is often seen as a result of degenerative change to the conducting system.
In younger patients, it may occur with ischaemic heart disease.
Other less common systemic causes are also recognised.
