Essential Revision Notes for MRCP Third Edition - PasTest

CardiologyPotassium and ECG changesThere is a reasonable correlation between plasmapotassium and ECG changes.• Hyperkalaemia• Tall T waves• Prolonged PR interval• Flattened/absent P waves• Very severe hyperkalaemia• Wide QRS• Sine wave pattern• Ventricular tachycardia/ventricularfibrillation/asystole• Hypokalaemia• Flat T waves, occasionally inverted• Prolonged PR interval• ST depression• Tall U wavesECG changes following coronary arterybypass surgery• U waves (hypothermia)• Saddle-shaped ST elevation (pericarditis)• PR-segment depression (pericarditis)• Low-voltage ECG in chest leads (pericardialeffusion)• Changing electrical alternans (alternating ECGaxis – cardiac tamponade)• S1Q3T3 (pulmonary embolus)• Atrial fibrillation• Q waves• ST-segment and T-wave changesElectrocardiographic techniques forprolonged monitoring• Holter monitoring: the ECG is monitored in oneor more leads for 24–72 h. The patient isencouraged to keep a diary in order to correlatesymptoms with ECG changes• External recorders: the patient keeps a monitorwith them for a period of days or weeks. At theonset of symptoms the monitor is placed to thechest and this records the ECG• Wearable loop recorders: the patient wears amonitor for several days or weeks. The devicerecords the ECG constantly on a self-erasingloop. At the time of symptoms, the patientactivates the recorder and a trace spanningsome several seconds before a period ofsymptoms to several minutes afterwards isstored• Implantable loop recorders: a loop recorder isimplanted subcutaneously in the pre-pectoralregion. The recorder is activated by the patientor according to pre-programmed parameters.Again the ECG data from several seconds beforesymptoms to several minutes after are stored;data are uploaded by telemetry. The battery lifeof the implantable loop recorder is approximately18 months1.2.2 EchocardiographyPrinciples of the techniqueSound waves emitted by a transducer are reflectedback differentially by tissues of variable acousticproperties. Moving structures (including fluid structures)reflect sound back as a function of their ownvelocity. The signal-to-noise ratio is improved byminimising the distance and number of acousticstructures between the transducer and the objectbeing recorded.A longitudinal beam differentiating structures byreflectivity plotted against time gives an M-modeimage. Allows accurate measurement of dimensions,eg LA size, end-diastolic dimension.A longitudinal beam measuring velocities gives aDoppler velocity – a continuous wave picks up thegreatest velocity along the line, a pulsed wavefocuses on a specific point and tissue Doppler on afixed point of myocardium. Velocities can be usedto calculate pressure gradients. Used to measurevalve gradients and wall motion parameters.A broad beam gives a two-dimensional movingimage that can be processed into a threedimensionalimage with appropriate echo probeand processing software. The standard windowspermit imaging of the cardiac chambers to assessstructural abnormalities and function.9