palpations and arrythmias Flashcards
what are ventricular extrasystoles?
- premature contraction of heart ventricles
- premature QRS complex on ECG, long duration
- most common form of cardiac arrhythmia
what is ventricular tachycardia?
regular fast heart rate arising from improper electrical activity in ventricles
what is AV nodal reentrent tachycardia?
abnormal fast heart rhythm
type of supra ventricular tachycardia (originate above bundle of his)
most common regular supra ventricular tachycardia
what can arrhythmias cause?
sudden death syncope heart failure chest pain dizziness palpitations
what are the 2 main types of arrhythmia?
bradycardia (<60bpm)
tachycardia (>100bpm)
what can tachycardias be subdivided into?
- supraventricular tachycardia (arise from atrium of AV junction)
- ventricular tachycardias (arise from ventricles)
what is the normal cardiac pacemaker?
sinus node
describe the modulation of the sinus node?
depolarises spontaneously
modulated by ANS
parasympathetic NS usually predominates
reduction in parasympathetic or increase in sympathetic can cause tachycardia and vice versa
what is normal sinus rate?
60-100
slightly faster in women
what characterises sinus rate on ECG?
upright p waves in leads I and II but inverted in AVR and V1
describe sinus arrhythmia?
- fluctuations in ANS cause phasic changes sinus discharge rate
- inspiration-decrease parasympathetic and increase HR on expiration HR falls
- normal variation
- predictable irregularities of pulse
describe sinus bradycardia?
<60bpm in day or <50bpm night
- usually asymptomatic
- normal in athletes due to increased vagal tone
what can the causes of both bradycardia’s and tachycardias be split into?
systemic or cardiac
what is sinus tachycardia?
sinus rate >100
describe the normal mechanism of spontaneous cardiac rhythmicity?
slow depolarisation of transmembrane voltage during diastole until threshold potential is reached and action potential of pacemaker cells takes off
in what situations is the mechanism of cardiac rhythmicity increased?
increasing rate of diastolic deplarisation
changing the threshold potential
eg sympathetic activation -> adrenaline release-> enhanced automaticity-> sinus tachycardia / escape rhythms / accelerated AV nodal rhythms
how can myocardial damage produce an arrhythmia?
myocardial damage can result in oscillations (after depolarisations) of the transmembrane potential at the end of the action potential which can reach threshold potential and produce an arrhythmia.
- early after depolarisations-occur before transmembrane potential reaches threshold
- delayed after depolarisations-when they develop after transmembrane potential is completed
what can exaggerate ‘after depolarisations’?
pacing catecholamines electrolyte disturbances hypoxia acidosis some medications-atrial tachycardias produced by digoxin toxicity are due to triggered activity
what is the mechanism of re-entry?
‘ring’ of cardiac tissue surrounds an inexcitable core such as in a region of scarred myocardium
tachycardia initiation:
one branch of pukinje fibres is refractory and the other is excitable. causing a unidirectional block. if conduction in the excitable branch is slow enough then refractory limb will recover and allow retrograde activation to complete the loop. if time to conduct around loop Is longer than refractory periods of tissue within the ring then this will be maintained.
this is how most regular paroxysmal tachycardias are produced
what are the potential causes of bradycardia?
failure of impulse formation (sinus bradycardia) or failure of impulse conduction from atria to ventricles (AV block)
what factors can cause bradycardia?
Intrinsic factors Extrinsic factors (that affect a normal sinus node)
what are the extrinsic factors that can cause bradycardia?
- hypothermia, hypothyroidism, cholestatic jaundice, raised intracranial pressure
- drugs such as beta blockers, antiarrythmics
- neurally mediated syndromes
what are the intrinsic factors that can cause bradycardia?
- acute ischaemia and infarction of sinus node (complication of acute MI)
- chronic degenerative changes such as fibrosis of atrium and sick sinus syndrome
what are neurally mediated syndromes?
due to reflex that can result in bradycardia and reflex peripheral vasodilation
present as syncope or presyncope