Cardiac Axis Flashcards
The normal cardiac axis lies between -… and +… degrees, as shown by the diagram below.
The normal cardiac axis lies between -30 and +90 degrees, as shown by the diagram below.
If the net effect of the action potentials through the heart is directed < -30 degrees, this is termed ….
If the net effect of the action potentials through the heart is directed < -30 degrees, this is termed left axis deviation (LAD). LAD could be due to a number of different pathologies (e.g. left anterior hemiblock, left ventricular hypertrophy). LAD is shown by a positive deflection in limb lead I and negative deflections in leads II and III.
If the net effect of the action potentials through the heart is directed > +90 degrees it is termed ….
Alternatively, if the net effect of the action potentials through the heart is directed > +90 degrees it is termed right axis deviation (RAD). RAD may be due to a number of different pathologies (e.g. right ventricular hypertrophy, left posterior hemiblock). RAD is shown by limb lead III having the greatest positive deflection on the ECG compared to leads I and II.
net effect of the action potentials through the heart is directed > +90 degrees?
> +90 degrees it is termed right axis deviation (RAD). RAD may be due to a number of different pathologies (e.g. right ventricular hypertrophy, left posterior hemiblock). RAD is shown by limb lead III having the greatest positive deflection on the ECG compared to leads I and II.
net effect of the action potentials through the heart is directed < -30 degrees?
< -30 degrees, this is termed left axis deviation (LAD). LAD could be due to a number of different pathologies (e.g. left anterior hemiblock, left ventricular hypertrophy). LAD is shown by a positive deflection in limb lead I and negative deflections in leads II and III.
… is shown by limb lead III having the greatest positive deflection on the ECG compared to leads I and II.
RAD is shown by limb lead III having the greatest positive deflection on the ECG compared to leads I and II.
A 38 year old intravenous drug use is admitted to hospital with high fevers and palpitations. He is a known intravenous drug use and was recently treated for cellulitis at an injection site. On this admission his MRSA swab was positive. He has very poor dentition and appears cachexic. On examination he is tachycardic (120 bpm) with blood pressure 134/68 mmHg. There is an early diastolic murmur and bibasal crackles on auscultation of the lung. Three sets of cultures are taken and he is started empirically on co-amoxclav. The working diagnosis is infective endocarditis and a transthoracic echocardiogram is organised for the next day. Initial blood cultures show gram positive cocci in clusters.
Which of the following is the most appropriate antibiotic?
A Clindamycin B Gentamicin C Rifampicin D Flucloxacillin (your answer) Vancomycin (correct answer)
Given the likely diagnosis of a Staphylococcus aureus IE and previous MRSA positivity, vancomycin would be the treatment of choice.
Any patient with suspected IE should be discussed with microbiology and ideally referred and reviewed by the IE team. The treatment of choice for a methicillin sensitive staphylococcus aureus (MSSA) would be flucloxacillin. If the patient has methicillin resistant staphylococcus aureus (MRSA), is at risk of this MRSA (e.g. MRSA swab positive) or has coagulase negative staphylococci (CoNS), then vancomycin would be the more appropriate option. In this case, the history of intravenous drug use is concerning for staphylococcus aureus infection and the finding of gram positive cocci in clusters suggests of staphylococci. Remember, Streptococci are gram positive organisms that appear in chains or as diplococci (e.g. streptococcus pneumoniae).
