Dysrythmias Flashcards
Discuss bloods supply of the SA node, AV node, bundles of HIS
SA -60% RA 40% LAD
AV- 90% RA 10% LAD (left dominant)
RBB and left anterior superior bundle are supplied via the LAD
Left posterior inferior bundle is supplied via the RAC
Discuss mechanims of dysrythmias
Enchanced automaticity refers to spontaneous depolarization in non pacemaker cells or depolarization at an abnormally low threshold in pacemaker cells
Classic examples of enhanced automaticity include the idioventricular rhythms of severe hyperkalaemia or myocardial ischemia and the junctional rhythm associated with digitalis toxicity
Triggered acitivty refers to abnormal impulses resulting from afterdepolarizations
Afterdepolarizations are fluctuations in membrane potential that occur as the resting potential is restored. They can occur just prior to resting potentional being reached (early afterdepolarizations) or after full resting potential is reached (delayed afterdepol)
-Typically seen in torsades
Re-entry dysrhtyhtmias arise from repititive conduction of impulses thorugh a slef sustaining circuit, TO maintain a re-entry one conduction pathway must have a londer refractory period than the other so that when an impuls exits one limb of the circuit it may reenter the other in a retrograde fashion
Discuss bradydysrythmias associated with sinus node
Sinus Brady
- P -wave normal morphology with a fixed P-P and R-R interval and a ventricular rate below 60 BPM
- Found in healthy individuals particulalry well conditioned atheltes - with high resting vagal tone
- Can be pathalogical randing from autonomic mediated syncope to haemoperitoneum or acute inferior wall myocardial infarction. Hypothermia, hypoxia, drug effects and intrinisc sinus node disease
Sinus dysrhythmia
- manifestation of the natural variation in heart rate that occurs during the respiratory cycle manifested on the surface ECG as normally conducted P wavs with a variable P-P interval
Sinus Arrest and sinoartrial exti block
- a lack of atrial depolarization can occur becuase of failure of the sinus node to generate an impulse or failure of impulse conduction out of the SA node (exit block)
- SA exit block is not uncommon to see dropped P wave in regularly occuring patterns 2:1, 3:1 and 4:1
- May be a manifistation of intrinsic SA nod disease but can also be seen under condition of increased vagal tone whether benign or pathologic.
Discuss sick sinus syndrome
Sick sinus syndrome is a group of dysrhtymias caused by disease of the sinus node and its surrounding tissues creating sinus bradyacrdai, sinus arrest or SA exit blocl.
A variant of SSS known as bradycardia-tachycardia syndrome is characterized by one or more of these bradydysrhythmias alternating wit a tachydysrhtyhmia typically AF
SSS is most commonly seen in elderly patient as a result of fibrotic degneration. It is also seen in cardiomyopathies, connective tissue disease and certain drug.
Long term management requires pacemaker placement
Discuss AV block
1st degree: is from prolonged conduction at the level of the atria, AV node or His-Purkinje system. On the ECG first degree AV block shows a prlonged PR interval >20 sec, typically with a narrow QRS complex.
-Normal variant in 2% of healthy adults
2nd degree
-one or more (but not all) atrial impulses fail to reach the ventricles. The conduction ratio is the number of P waves to the number of QRS complexes over a period of time
#Type 1 (Wenckebach, Mobitz 1)
-Associated with progressive impairment of conduction within the AV node. THe surface ECG shows a lengthening of the PR interval from beat to beat until a P wave is entirely blocked
-Occur in a variety of conditions, these are associated with increased vagal tone and do not require specific treatment if stable
-IN MI type 1 is generally transiet with a good prognosis
# Type 2 (Mobitz 2)m
-Conduction block just below the level of the AV node
-No realative refractory period – all or non conduction
-On the surface ECG conduction of atrial impulses is sporadic and typically periodic but the PR interval dose not widen from beat to beat.
-Usually narrow but concomitant bundle branch blocks can occur
-Arise as a result of senescent degeneration, drug toxicity, ischaemia or other pathological condition and generally carry worse prognosis than type1
- In MI type 2 is associated with anterior wall injury and is oftern a precursor to complete heart block
3rd degree (complete)
- Often accompanied by a slow escape rhythm with width depending on the origin of the escape complex
- pacemaker above the bundle of HIS are generally narrow and at a rate of 45-60BPM
- Below the bundle 30-45 BPM and wide
- Hallmark is AV dissociation with an RR interval longer than the PP intraval
- The presence of AV dissociation with an RR interval shorter than the PP interval does not imply 3rd degree block
- Classically associated with digitalis, also seen in congenital pathology, acute ischaemia, tox and some infectious disease (CHaga’s disease, Lyme)
Discuss Approach to symptomtaic bradycardia
Atropine 600-1000mic Q5minutely
Isoprenaline or adrenaline at 2mic/min up to 10 mic/minute as needed
transcutaneous pacing
transvenous pacing /pacemaker
Describe approach to transcutaneous pacing and define electrical and mechanical capture
Indications
- symptomatic bradycardia unresponsive to drug therapy
- 3rd degree heart block
- Mobitz 2 if unstable
- overdrive pacing
Method
- Place pads ideally in AP position
- Connect ECG leads
- Set pacemaker to demand
- Turn pacing rate to 30BPM greater than patient intrinsic rate
- Set mA to 70
- Start pacing and increase mA until pacing rate capture on monitor
- If pacing rate not capture at 120-130mA- resit electrodes
- Once pacing captured set current at 5-10mA above threshold
Electrical capture: each pace marker is followed by a wide QRS and t-wave
Mechanical capture: Electrical capture with output
Describe sinus tachy
Narrow complex tachycardia wiht normal p waves preceding each QRS complex on the ECG
IN adult rarely exceeds 170 and in infants rarley 200-225
Describe atrial tachycardia
Atrial rhythm with more tahn 100 QRS complexes/min arising from a non-sinus node site within the left or right atrium.
The ECG hallmark of AT is morphologically abnromal P-waves all mostly related to a QRS - depedning on the atrial rate the conduction can be 1:1 or 2:1 or higher.
Multifocal atrial tachycadia is a form of AT wiht three or more distinct P wave morphologies and varying PR and PP intervals from the multiple ectopic atrial foci. MAT is associated with
-pulmonary disease in up to 60% (COPD)
-Can be seen in primary cardiac pathology
HR >100 can be as high as 250 (usually 100-150)
For both MAT and AT – treat underlying causes - as they are aften precipitated by the underlying illnes DC cardioversion often fails
List causes of completely irregular rhythms
AF
- AT or flutter with varying conduction
- MAT
- Multiple extrasystoles
- Wandering pacemaker
- parasystole
Describe AF
Is identified by electrical chaos - it starts from unpatterned depolarisation of atrial tissue caused by multiple re-rentry circuits generating 300-600 impulses/min
-Reduces cardiac output from a loss of co-ordination of atial contraction and from rapid ventricular rate both of which limit diastolic filling.
Patients with atrial fibrillation can develop left atrial thrombi especially in the left atrial appendage and consequent embolic events
Typically the ventricualr rate does not exceed 150-170 BPM and often is slower particularly in the presence of nodal blocking agents.
AF with rates exceeding 200 strongly suggested accessory pathways
Describe Ashman phenomenon
Aberrant ventricular conduction of an early arriving atrial impulse following a relatively long R-R interval the result of a partially refractory HIS bunde
Characterised by short salvo of widened QRS following a particularly long RR interval
List causes of AF
CVS
- HTN
- cardiomyopathy
- IHD
- Valvular disease
- CCF
- SSS
- Pericarditis
- Myocardial contusion
- Cardiac surgery
- accessory pathways -WPW
ENdo
-Thyroid
Res
-PE
Discuss management of AF
Rate or rhythm control
if unstable DC cardioversion
Rate - metoprolol, magnesium, treat underlying cause
Discuss AFFIRM and RACE trials
The AFFIRM and RACE trial demonstarted that embolic events occurred with equal frequency regardless of whether rate or rhythm control was pursued. Further more most embolic events occured after anticoagulation had been stopped and indicates taht patients with rate control should still be anticoagulated as per chadsvasc and has bled
There are at least 3 explanation for the above
1) despite successful cardioversion and antiarryhtmic drug therapy teh recurrence rate of either intermittent or persistent AF is 35-60% at one year with intermittent monitoring and 88% with continuous
- up to 90% of AF recurrence are asymptomatic and episdoes lasting more than 48 hours are not uncommon - enough time for left atrial appendage thrombi to form
2) patients with nonvalvular AF that is not due to reversible disease often ahve other predisposing risks for stroke
3) there may be discordance between the body of the left atrium demonstrating sinus mechanims while the atrial appendage dispalys an AF contraction pattern
