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
RESPIRATORY VARIATION EFFECTS ON THORACIC PRESSURE
Negative inspiratory efforts -> Use end-expiratory pressure in respiratory cycle to estimate R heart pressures
- 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
- 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)
- 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.
FINDING THE END-EXPIRATORY WAVES ON RA PRESSURE WAVES AND COMPARING TO EKG
- 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
- 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
- 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
- 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
- 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)
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
