Cardiac arrhythmias Flashcards
What symptoms may arrhythmias cause?
sudden death, syncope, heart failure, chest pain, dizziness, palpitations or no symptoms at all
How is the rate of sinus node discharge modulated?
The autonomic nervous system
What is sinus arrhythmia?
Fluctuations of autonomic tone result in phasic changes of the sinus discharge rate. During inspiration, parasympathetic tone falls and the heart rate quickens; on expiration, the heart rate falls. This variation is normal, particularly in children and young adults. Typically, sinus arrhythmia results in predictable irregularities of the pulse.
What is sinus bradycardia?
A sinus rate of <60 b.p.m. during the day or <50 b.p.m. at night is known as sinus bradycardia. It is usually asymptomatic unless the rate is very slow. Sinus bradycardia is normal in athletes owing to increased vagal tone.
What are the common extrinsic causes of sinus bradycardia?
- hypothermia, hypothyroidism, cholestatic jaundice and raised intracranial pressure
- drug therapy with beta-blockers, digitalis and other antiarrhythmic drugs
- neurally mediated syndromes
What are the common intrinsic causes of sinus bradycardia?
- acute ischaemia and infarction of the sinus node (as a complication of acute myocardial infarction)
- chronic degenerative changes, such as fibrosis of the atrium and sinus node (sick sinus syndrome)
What causes sick sinus syndrome (sinoatrial disease)?
It is usually caused by idiopathic fibrosis of the sinus node. Other causes of fibrosis, such as ischaemic heart disease, cardiomyopathy or myocarditis, can also cause the syndrome.
What are neutrally mediated syndromes in reference to arrhythmias?
Neurally mediated syndromes are due to a reflex (called Bezold–Jarisch) that may result in both bradycardia (sinus bradycardia, sinus arrest and AV block) and reflex peripheral vasodilatation. These syndromes usually present as syncope or pre-syncope (dizzy spells).
What is carotid sinus syndrome?
It occurs in the elderly and mainly leads to bradycardia. Syncope occurs
What is neurocardiogenic (vasovagal) syncope (syndrome)?
It usually presents in young adults but may present for the first time in elderly patients. It results from a variety of situations (physical and emotional) that affect the autonomic nervous system. The efferent output may be predominantly bradycardic, predominantly vasodilatory or mixed.
What is postural orthostatic tachycardia syndrome?
It is a sudden and significant increase in heart rate associated with normal or mildly reduced blood pressure and produced by standing. The underlying mechanism is a failure of the peripheral vasculature to constrict appropriately in response to orthostatic stress, which is compensated by an excessive increase in heart rate.
How is sinus bradycardia managed?
The management of sinus bradycardia is first to identify and then, if possible, to remove any extrinsic causes. Temporary pacing may be employed in patients with reversible causes until a normal sinus rate is restored, and in patients with chronic degenerative conditions until a permanent pacemaker is implanted.
How is chronic symptomatic sick sinus syndrome managed?
Chronic symptomatic sick sinus syndrome requires permanent pacing (DDD), with additional antiarrhythmic drugs (or ablation therapy) to manage any tachycardic element. Thromboembolism is common in tachy–brady syndrome and patients should be anticoagulated unless there is a contraindication.
A patient presents with carotid sinus hypersensitivity, where the symptoms are reproduced by a cardiac massage and life-threatening causes of syncope have been excluded. What will be beneficial for them?
Pacemaker implantation
What are the treatment options in vasovagal attacks?
- avoidance, if possible, of situations known to cause syncope in a particular patient, and sitting/lying down and applying counter-pressure manœuvres (pushing the palms together or crossing the legs) if an attack threatens
- Increased salt intake, compression of the lower legs with hose, and drugs such as beta-blockers, alpha-agonists (e.g. midodrine) or myocardial negative inotropes (e.g. disopyramide) may be helpful.
What is helpful for patients with “malignant” neorocariogenic syncope (syncope associated with injuries and demonstrated asystole)?
Permanent pacemaker therapy. These patients benefit from dual-chamber pacemakers with a feature called ‘rate drop response’, which, once activated, paces the heart at a fast rate for a set period of time in order to prevent syncope.
What is first-degree heart block?
This is a simple prolongation of the PR interval to >0.22 s. Every atrial depolarization is followed by conduction to the ventricles but with delay
What is second-degree heart block?
This occurs when some P waves conduct and others do not. There are several forms:
• Mobitz I block (Wenckebach block phenomenon) is progressive PR interval prolongation until a P wave fails to conduct. The PR interval before the blocked P wave is much longer than the PR interval after the blocked P wave.
• Mobitz II block occurs when a dropped QRS complex is not preceded by progressive PR interval prolongation. Usually, the QRS complex is wide (>0.12 s).
• 2 : 1 or 3 : 1 (advanced) block occurs when every second or third P wave conducts to the ventricles. This form of second-degree block is neither Mobitz I nor II.
What is a Wenckebach AV block generally due to?
A block in the AV node
What is a Mobitz II block generally due to?
A block at an infra-nodal level, such as the His bundle
True or false? Acute myocardial infarction may produce first-degree heart block?
False: It may produce second-degree heart block
In anterior myocardial infarction, what second-degree heart block associated with?
A high risk of progression to complete heart block (temporary pacing followed by permanent pacemaker implantation is usually indicated)
What is third degree (complete) AV block?
Complete heart block occurs when all atrial activity fails to conduct to the ventricles. In patients with complete heart block, the aetiology needs to be established. In this situation, life is maintained by a spontaneous escape rhythm.
What should one look for when assessing a patient with complete heart block?
Are there signs of haemodynamic compromise?
- chest pain
- breathlessness
- poor urine output
- impaired consciousness (AVPU: Alert, responds to Voice, responds to Pain, Unresponsive), often governed by the blood pressure:
- hypertensive: compensating … for now
- hypotensive: needs urgent intervention
Is there a reversible cause?
- beta-blocker, a calcium-channel blocker, digoxin overdose
- disturbed acid-base and electrolyte imbalance.
If the patient is currently stable, what is the escape rhythm like?
- narrow-complex and relatively normal in rate
- broad- complex and very slow.
What can be done to support a patient with third-degree AV block?
Supportive adjuncts during this time can be a reversal of toxins/drugs, support with vasopressors (e.g. adrenaline (epinephrine)), attempts to speed the sinus rate with isoprenaline and temporary pacing, either transcutaneously or transvenously.
What are the reversible causes of complete heart block?
· Drugs
· Autoimmune or infectious conditions if treated promptly without permanent myocardial fibrosis
· Acute myocardial infarction
· Immediate post-cardiac surgery
What are the non-reversible causes of heart block?
· Ischaemic cardiomyopathy (consider implantable cardioverter-defibrillator and biventricular device) · Structural heart disease · Progressive neurological conditions · Iatrogenic causes · Biventricular device
What are the congenital causes of complete heart block?
- Autoimmune (e.g. maternal SLE)
* Structural heart disease (e.g. transposition of great vessels)
What are the idiopathic causes of complete heart block?
- Lev’s disease (progressive fibrosis of distal His–Purkinje system in elderly patients)
- Lenegre’s disease (proximal His–Purkinje fibrosis in younger patients)
What are the causes of ischaemic heart disease that can cause complete heart block?
- Acute myocardial infarct
* Ischaemic cardiomyopathy
What are the non-ischaemic heart disease causes of complete heart block?
- Calcific aortic stenosis
- Idiopathic dilated cardiomyopathy
- Infiltrations (e.g. amyloidosis, sarcoidosis, neoplasia)
What types of cardiac surgery can cause complete heart block?
Following aortic valve replacement, CABG, VSD repair
What are the iatrogenic causes of complete heart block?
Radiofrequency AV node ablation and pacemaker implantation
Give examples of drugs that can cause complete heart block
Digoxin, beta-blockers, non-dihydropyridine calcium-channel blockers, amiodarone
What infections can cause complete heart block?
- Endocarditis
- Lyme disease
- Chagas’ disease
Give examples of autoimmune conditions that can cause complete heart block
SLE, rheumatoid arthritis