PCWP

Question 1

PCWP procedure

Answer 1

introduction of a KT w balloon tip into PA => inflation of balloon into PA segment => fluid filled window into LA (transmitted through PVs, capillary bed)
o Indirect recording of mechanical LA event/pressure
o Cannot be recorded continuously = would damage PA

Question 2

PCWP tracing interpretation

Answer 2

• Retrograde transmission => delay btw ECG and mechanical events because transmitted into pulmonary capillary bed (can vary according to distance travelled)
• A wave follows ECG P wave by 200ms = LA systole
• X descent: LA relaxation
  o Sudden downward motion of MV annulus in early LV systole
• C wave = closure of MV valve => onset of LV systole
  o Often not seen on wedge waveform (damping)
• V wave = LA venous filling
  o Peak = end of LV systole => occur after T wave
  o => if LA volume overload = MR, VSD
• Y descent: rapid exit of blood LA => LV
   Onset of LV diastole

Question 3

Clinical use of PCWP

Answer 3

• Assess adequacy of LV filling
• Measure hydrostatic pressures of PVs
  o Dx of pulmonary edema: >24mmHg
  o Known lag btwn improvement in wedge pressure vs CTX
• Normal mean = 2-12mmHg
  o Should be 2xRAP
  o Approx 0-5mmHg lower vs PA diastolic pressure unless incr PVR

Question 4

Limitations of PCWP

Answer 4

Sometimes inaccurate depending on underlying condition

• Mean wedge pressure should always < mean PA pressure
• incr PA pressure => falsely elevated wedge pressure
• Accurate high quality wedge pressure: uninterrupted fluid column

Question 5

Conditions where wedge pressure is accurate for LA but not LV end diastolic pressure

Answer 5

 MS: mean wedge overestimate LV filling pressures
 MR w large V wave
 Non compliant LV

Question 6

Conditions where wedge pressure is inaccurate for LAP

Answer 6

 Abnormal pulmonary vascular bed
 incr intrathoracic pressure => collapse of pulmonary capillary bed
 decr mean LAP => collapse of flaccid pulmonary capillaries w normal intrathoracic P
 Cor tritriatum in cats

Question 7

PCWP: 3 physiologic pressure zones

Answer 7

 Zone 1: apex of lungs => alveolar > mean PA and PV pressures
 Zone 2: central portion of lungs => PA > alveolar > PV pressures
 Zone 3: base of the lungs => alveolar < mean PA and PV pressures
* Accurate measure of pressure via wedge because of direct transmission from LA to KT tip

Question 8

High quality wedge pressure

Answer 8

 Well defined A and V waves
 Fluoro confirmation of KT placement in distal PA, no apparent motion of KT w inflated balloon
 O2 saturation from KT >90%
 incr mean pressure when balloon deflated or KT withdrawn.
o Overwedged pressure: KT is in peripheral PA w overinflated balloon  PA rupture