Essential Revision Notes for MRCP Third Edition - PasTest

CardiologyProarrhythmic causes of abnormalrepolarisation (ST-T changes)• Familial• Long QT syndromes 1–5• Brugada syndrome• Short QT syndrome• Arrhythmogenic right ventriculardysplasia• Drugs• Quinidine• Erythromycin• Amiodarone• Tricyclic antidepressants• Phenothiazines• Probucol• Non-sedating antihistamines(eg terfenadine)• Ischaemic heart disease• Metabolic• Hypocalcaemia• Hypothyroidism• Hypothermia• Hypokalaemia• Rheumatic carditisLong QT syndromes: The corrected QT is .540 ms(normal ¼ 380–460 ms). Ninety per cent are familial,with chromosome 11 defects being common(Romano–Ward syndrome has autosomal dominantinheritance; Jervell–Lange-Nielsen syndrome isautosomal recessive and associated with congenitaldeafness). Arrhythmias may be reduced by a combinationof â-blockers and pacing.Cardiac causes of electromechanicaldissociationWhen faced with a cardiac arrest situation it isimportant to appreciate the list of causes of electromechanicaldissociation (EMD):• Hypoxia• Hypovolaemia• Hypokalaemia/hyperkalaemia• Hypothermia• Tension pneumothorax• Tamponade• Toxic/therapeutic disturbance• Thromboembolic/mechanical obstruction1.5.5 Pacing and ablation proceduresTemporary pacingThe ECG will show LBBB morphology (unless thereis septal perforation, when it is RBBB). Pacing maybe ventricular (right ventricle apex) or AV (atrialappendage and right ventricle apex) for optimisedcardiac output.Complications include:• Crossing the tricuspid valve during insertion,which causes ventricular ectopics, as doesirritating the outflow tract• Atrial or right ventricular perforation andpericardial effusion• Pneumothorax: internal jugular route ispreferable to the subclavian one, as it minimisesthis risk and also allows control after inadvertentarterial puncturesPermanent pacingMore complex permanent pacing systems includerate-responsive models, which use movement sensorsor physiological triggers (respiratory rate or QTinterval) to increase heart rates. Although moreexpensive they avoid causing pacemaker syndromeand they act more physiologically for optimal leftventricular function.29