Arrhythmias Notes

Arrythmias Normal Conduction in heart ? SA node o 'Cardiac pacemaker' o Posterior wall of atrium ? AV node o postero-inferior atrial spetum o Slow conduction velocity (0.05 m/s) to ensure atrial contraction preceeds ventricular ? Bundle branches and purkinje ? Subendocardium, fast conducting, produce rapid (narrow complex) synchronous systole ? Normally o SAN stimulates impulses o Spreads over atria in co-ordinated fashion to cause atrial contraction o Stimulation of the AVN o Conduction down the bundle of His to the bundle branches following a delay to ensure synchronous contraction o Subsequent conduction in the Purkinje system is rapid to ensure a narrow complex o Rapid ventricular systole ? Arrhythmias occurs when this process is disrupted. Heart Block ? Total heart block=block in the conducting system between the atria and ventricles ? P-waves don't correspond to QRS ? Block in the bundle branches then QRS complexes must be generated in the ventricles independently from the atria o Due to left or right bundle branch block or the presence of ventricular arrhythmias=QRS complexes will be broad (as the bundle/Purkinje system is that which ensures narrow complexes) Ventricular tachycardia (broad complex) ? Def= Tachycardia arising in the ventricles due usually with re-entry ? Causes o CAD o MI o Hypokalaemia ? Features: o Asymptomatic o Palpitations o Syncope o Cardiogenic shock ? Pathophysiology o Increased rate reduces diastolic filling time o Leads to reduced cardiac function o Cardiogenic shock (reduced BP, raised JVP) o Very serious, high mortality! ? ECG o Broad complex (>3sq) - pacemaking occurring in ventricles without conduction through AVN/Purkinje which acts to narrow QRS o Regular o Assume any broad complex tachycardia is VT until proven otherwise 

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