Cardiac Flashcards
+ve inotropy
Increases SV & systolic pressure.
Reduces RR interval. Affects stoke index.
Does NOT increase ventricular end diastolic pressure.
Windkessel effect
Describe elastic force of aorta; the compressive force which occurs after LV systole & closure of Ao valve. Seen as dicrotic notch in arterial waveforms.
Cannon a waves seen in
RA contraction against closed tricuspid valve:
Junctional rhythm.
AV block; esp 3rd degree.
VT.
Congenital heart blocks.
Constrictive pericarditis.
Pulm HTN.
Y descent is due to
Opening of tricuspid valve and blood draining into RV.
X descent occurs in
Ventricular systole: when blood leaves the ventricle.
A wave correspondent in ECG
Corresponds to p wave. (Just after)
Major determinants of myocardial oxygen consumption?
Ventricular wall tension.
Contractility.
Heart rate.
Requirements of myocardial oxygen consumption?
Arterial & venous content (aortic root & coronary sinus), and est of total coronary flow
Myocardial substrates for work other than O2
Glucose- 40% (insulin influence).
Fatty acids- 60%.
Ketones when conditions dictate.
What is the O2 extraction ratio of the myocardium?
About 70%; pretty much maximum.
Blood returning to coronary sinus has PO2 <3kPa. Heavy on the aerobic metabolism.
Stages of pressure-volume loop for LV includes:
1- Mitral valve opening - start of diastolic filling.
2- mitral valve closure at start of systole- isovolumetric contraction phase.
3- Ao valve opening at start of ejection phase.
4- Ao valve closure at start of isovolumetric relaxation phase.
On LV pressure-vol loop, what are the effective work and the total work?
Effective work is the stroke work, which is represented by the area within the loop.
Total work is the effective work plus the potential energy (represented by area before stroke work when systolic & diastolic elastance curves are drawn)
What are the determinants of stroke volume?
Preload (Starling’s law) & afterload (force opposing ventricular wall- tension).
Contractility (extrinsic influence e.g. calcium and sympathetic input).
Ventricular systolic & diastolic function (relaxation).
Alternative equation for MAP?
MAP= (2/3 DBP) + (1/3 SBP)
Hence = DBP + (SBP-DBP)/3
What are the determinants of myocardial oxygen consumption?
Primarily heart rate, contractility, and intra-myocardial tension. (Ventricular work)
Normal ranges for oesophageal Doppler monitoring
CO 5-8L/min.
Stroke vol 55-100ml.
PV 70-100cm/sec.
FTc 330-360 msecs. (FTc: flow time corrected to HR 60bpm, so as to compare it more appropriately with other variables.)
A fluid responsive patient under oesophageal Doppler monitoring should show…
Increased stroke vol/ stroke distance of >10% is seen as positive response; challenge should be repeated.
Failure to respond to fluid challenge should then be lead to inotropic agents consideration, and possibly vasodilators.
Hypertrophy of the heart in athletes is similar to that in chronic hypertension?
True, but the athletic heart dose not demonstrate diastolic dysfunction.
Furthermore, SV can increase from 70ml to 140ml in trained male. (hence decreased resting heart rate to maintain same cardiac output). Max SV in training increases from 100 to 190ml in males.
