NORMAL PRESSURES IN THE HEART

  • RA 1-5 mmHg
  • RV 25/5 mmHg
  • PA 20/10 mmHg
  • LA 3-12 mmHg (PCWP estimates the LA pressure)
  • LV 120/12 mmHg

Screen Shot 2020-04-01 at 20.01.25

RESPIRATORY VARIATION EFFECTS ON THORACIC PRESSURE

Negative inspiratory efforts -> Use end-expiratory pressure in respiratory cycle to estimate R heart pressures

Screen Shot 2020-04-01 at 20.36.08.png

  • end-expiratory pressure most closely resembles atmospheric pressure with negative pressure breathing
  • though you may be tempted to say that beginning of inspiration closely resembles atmospheric pressure–this is true, but the expiratory phase is naturally much longer/easier to catch than beginning of inspiration

Positive pressure/mechanical ventilation -> Use opposite approach compared to neg inspiratory efforts; use end-inspiratory pressure

Screen Shot 2020-04-01 at 20.37.10.png

  • inspiratory phase will increase the thoracic pressure and impair venous filling and impair venous return
  • use end-inspiratory pressure in mechanically ventilated patient (? not sure why this is; seems like an error)

RIGHT HEART CATH WAVEFORMS (STARTING WITH RA WAVEFORM)

Screen Shot 2020-04-01 at 20.37.29.png

  • a-wave -> follows P wave on rhythm strip by 80 ms
    • pressure increase from atrial contraction
    • “atrial kick” of final bolus pumped into the RV prior to RV systole
  • v-wave -> passive venous filling of atria from/after ventricular systole
    • corresponds to t-wave from rhythm strip
  • c-wave -> sometimes seen; tricuspid annulus towards the RA at onset of ventricular systole
  • x-descent -> atrial relaxation; downward motion of AV junction
  • y-descent -> rapid emptying of the RA after the TV opens

*anecdotally, we use the term “c-v wave”/combine the c-wave and v-wave on the pressure waveforms in practice to more easily compare them to the EKG lead–i.e. treat c-wave and v-wave as one entity.

cvp-waveforms.jpg

FINDING THE END-EXPIRATORY WAVES ON RA PRESSURE WAVES AND COMPARING TO EKG

Screen Shot 2020-04-01 at 20.38.27.png

  • this picture chose R heart cath waves at the peak, but definitely staying away from the valleys
  • a-wave -> identified by drawing line down from the P-wave
  • v-wave -> identified by drawing line down from the T-wave

COMPARING THE RV WAVEFORM WITH EKG

Screen Shot 2020-04-01 at 20.39.27.png

  • delay in the RV wave systole from the EKG QRS wave reflects the delay in pressure wave traveling thru the pulmonary circulation 110 cm PA catheter
  • RV diastole pressure wave is flat/low slope to reflect the RV compliance/ability to stretch
    • “black circle” above is the RV diastole
    • “green arrow” is where likely location of a-wave would be

FINDING THE RV SYSTOLE AND DIASTOLE PRESSURES VIA WAVEFORM

Screen Shot 2020-04-01 at 20.40.02.png

  • systolic pressure -> from the wave that just follows the peaked waveform (i.e. this is the end-expiratory wave)
    • if you picked the highest wave, then exhalation is still occurring; thus, pick just one after the peak
  • diastolic pressure -> the valley preceding the systole that you just chose

PULMONARY ARTERY WAVEFORM

Screen Shot 2020-04-01 at 20.40.47.png

  • diastolic step-up clearly seen on PA compared to RV waveform
  • RV systole still remains same as PA systole
  • “green arrow” -> closure of the pulmonic valve which is on the descent side of the PA systolic wave
  • peak pulmonary artery pressure occurs within the T-wave on EKG

Screen Shot 2020-04-01 at 20.41.57.png

  • end-expiratory waveform for the PA wave
    • choose the systole from wave right after the peak (i.e. since peak wave will be during when exhalation is still occurring, choose the one right after for end-expiration)
  • again, the peak/systole of the PA waveform occurs during the T-wave on the EKG (just like in the RV waveform)
  • diastolic PA pressure -> choose the valley right before the chosen PA systole (seen as circles in the image below)

Screen Shot 2020-04-01 at 20.42.23.png

DIFFERENCES BETWEEN THE PCWP WAVEFORM AND THE RA WAVEFORM

  • a-wave -> time delay with a-wave compared to EKG P-wave
    • since pressure has to traverse the pulm capillary bed
    • therefore, the a-wave will be 240 ms following the P-wave on EKG
    • the a-wave will correspond to the end of the QRS complex
  • c-wave is absent on wedge -> LA pressure is transmitted thru the pulmonary capillary bed which dampens the wave by the time reaches the PA catheter
  • PCWP is indicated by a-wave
    • found at the end of the corresponding QRS wave
    • located at end-expiration
    • the machine averages the two a-waves on the image below and reports that as PCWP

Screen Shot 2020-04-01 at 21.59.38.png

 

 

 

 

 

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