Right Heart Catheterization — Technique and Measurement

Definition

The measurement half of right heart catheterisation is a sequence of decisions — where the catheter sits, where zero is, which phase of the breath and of the cardiac cycle the pressure is read in, and which method measures output — and each one moves the number. A pressure recorded with the wrong zero, read against the wrong part of the waveform, or paired with an output from an inappropriate method is still a number, and it will still be acted on.

Key Concepts

Access, Position and Zero Reference

• The patient must be supine. Semi-supine posture, raised legs or a moved arm alters pressure and output enough to change an interpretation. (sources/rhc-hf-ehj-2025, rating: high)
• The right internal jugular vein under ultrasound guidance is the preferred access: it reduces bleeding complications. The femoral route remains an alternative, at the cost of higher infection risk, a need for fluoroscopy and post-procedural bedrest. (sources/rhc-hf-ehj-2025, rating: high)
• Zero at the mid-thoracic level, which corresponds to the left atrium in most patients. Every 1 cm of error changes the measured pressure by about 0.8 mmHg — which matters little for a pulmonary artery pressure and a great deal for a wedge pressure. (sources/rhc-hf-ehj-2025)
• For upright exercise the transducer sits at the phlebostatic axis, the intersection of the fourth intercostal space and the mid-chest; the right atrial level is marked on the chest wall fluoroscopically before the patient stands. (sources/hemodynamic-hf-pht-aha-2026, rating: very high)

Cardiac Output Measurement

• Direct Fick is the reference method and requires measured oxygen consumption — a Douglas bag or metabolic cart, which most laboratories do not have. (sources/rhc-hf-ehj-2025, rating: high)
• Indirect Fick is confirmed inaccurate. Its formulae were derived in infants, children or highly selected healthy adults and do not describe contemporary cardiac patients; thermodilution is preferred wherever it is valid. It cannot be estimated during exercise at all, because pulmonary artery saturation falls in a way that fixed formulae do not capture. (sources/hemodynamic-hf-pht-aha-2026, rating: very high)
• Thermodilution: inject 10 mL of saline at a known temperature, average three values within 10% of each other, and inject at the same phase of the respiratory cycle to improve precision. It remains accurate in significant tricuspid regurgitation — contrary to common belief — but is unreliable in intracardiac shunts and on ECMO. (sources/rhc-hf-ehj-2025; sources/hemodynamic-hf-pht-aha-2026)
• Sources of thermodilution error — injectate warming, catheter conductive losses, respiratory cycling, recirculation — and the comparison with pulse contour and lithium dilution methods are set out on concepts/Cardiac-Output-Measurement. (sources/co-indicator-anesthanalg-2010, rating: high)
• Cardiac magnetic resonance with quantitative flow is the reliable alternative when a shunt or severe regurgitation makes thermodilution invalid. (sources/rhc-hf-ehj-2025)
• Cardiac index (output divided by body surface area) is preferred to absolute output in clinical use. (sources/rhc-hf-ehj-2025)
• An output error propagates straight into pulmonary vascular resistance. Overestimate the output and the resistance falls, potentially excluding pulmonary arterial hypertension; underestimate it and the resistance rises, potentially labelling a patient as having it. (sources/rhc-hf-ehj-2025)

PAWP Technique

• Read the wedge pressure at end-diastole, just before the C-wave, taking the mean of the a-wave; avoid measurement during or immediately after ectopic beats. (sources/rhc-hf-ehj-2025, rating: high)
• In atrial fibrillation, measure 130–160 ms after QRS onset, before the V-wave. The value may still overestimate left ventricular end-diastolic pressure, and direct measurement of LVEDP is the fallback when it looks implausible. (sources/hemodynamic-hf-pht-aha-2026, rating: very high)
• Large V-waves — severe mitral regurgitation, poor left atrial compliance, ventricular septal defect — force a choice: use the mean wedge pressure including V-waves for resistance calculations, and the mean excluding them to estimate ventricular end-diastolic pressure. (sources/hemodynamic-hf-pht-aha-2026)
• Two rules of thumb check the tracing: the wedge pressure must be at or below diastolic pulmonary artery pressure, and clear a- and v-waves must be visible. If the c-wave is indeterminate, gate the measurement to the QRS — valid only in the absence of large V-waves. (sources/rhc-hf-ehj-2025)
• Confirm the wedge. Discard the first 5–10 mL, then show that the wedged saturation is within 3–5% of systemic pulse oximetry. (sources/hemodynamic-hf-pht-aha-2026)
• Over-wedging — an over-inflated balloon — abolishes the a- and v-waves and falsely raises the wedge pressure. Deflate, retract into the right ventricle and re-advance. (sources/rhc-hf-ehj-2025)

Respiratory Cycle and Procedural Conduct

• All pressures are read at end-expiration, without breath-holding or a Valsalva manoeuvre. Where respiratory swings are large — COPD, obesity, mechanical ventilation, hyperventilation — average across three or four cycles, or report both the end-expiratory and the averaged value. (sources/rhc-hf-ehj-2025, rating: high; sources/hemodynamic-hf-pht-aha-2026, rating: very high)
• Fasting is not required and prescribed medications continue. Defer intravenous sedation, which alters breathing pattern and vascular tone; topical or local anaesthesia is preferred, with oral premedication if anxiolysis is needed. (sources/hemodynamic-hf-pht-aha-2026)
• Do not read from automated monitor averages: the algorithms account for neither respiration nor ectopy. (sources/hemodynamic-hf-pht-aha-2026)
• Measure in euvolemia where possible. After aggressive diuresis the wedge pressure is falsely low, which overestimates pulmonary vascular resistance and can manufacture a pre-capillary diagnosis. In decompensated states, ventricular interdependence raises the wedge pressure and mimics isolated post-capillary physiology. Diurese first. (sources/rhc-hf-ehj-2025)

Mixed Venous Saturation and Shunt Detection

• Sample from the pulmonary artery. A saturation above 75% should prompt a stepwise oximetry run to exclude a left-to-right shunt. (sources/rhc-hf-ehj-2025, rating: high)
• It falls in progressive cardiogenic shock (Stages C–E) and rises in late septic shock. (sources/rhc-hf-ehj-2025)

Safety and Contraindications

• Serious adverse events occur in about 1.1% and procedure-related death in about 0.055% in experienced pulmonary hypertension centres. (sources/rhc-hf-ehj-2025, rating: high)
• Pulmonary artery perforation is the feared complication. Relative contraindications are right atrial or ventricular thrombus or tumour, a pacemaker implanted within the past month, a mechanical right heart valve and a tricuspid clip. (sources/rhc-hf-ehj-2025)

Reference Values

(sources/rhc-hf-ehj-2025, rating: high)

The normal ranges are not uniform across sources. The practical-guidance review gives RA 0–6, RV systolic 20–34 and diastolic 0–6, PA systolic 20–34 and diastolic 8–12, and PCWP 4–14 mmHg (sources/rhc-hf-jacchf-2024, rating: high). Two entries above differ from that set and are left visible rather than reconciled: RAP is given as 2–6 mmHg here against 0–6 there, and PAWP as ≤13 mmHg against a 4–14 mmHg range. The gaps reflect different reference populations rather than a dispute about physiology, but a right atrial pressure of 1 mmHg or a wedge pressure of 14 mmHg sits inside one range and outside the other — so a quoted "normal" should name its source.

Contradictions / Open Questions

• The two principal sources disagree on normal ranges. Right atrial pressure is 2–6 mmHg in one and 0–6 in the other; the wedge pressure is ≤13 mmHg in one and 4–14 in the other. The table retains both values rather than choosing, because neither source explains its reference population. (sources/rhc-hf-ehj-2025, rating: high; sources/rhc-hf-jacchf-2024, rating: high)
• Thermodilution in significant tricuspid regurgitation is contested. One synthesis states it remains accurate, contrary to common belief; the methodological comparison reports error that changes direction with flow state — overestimation in low flow, underestimation in high flow — and does not settle the severity dependence. The likely explanation is that the two bodies of work studied different grades of regurgitation decades apart, which no study has reconciled. (sources/rhc-hf-ehj-2025; sources/co-indicator-anesthanalg-2010)
• The reference method is the least available one. Direct Fick is the standard and requires measured oxygen consumption; indirect Fick is confirmed inaccurate. Most laboratories therefore report thermodilution by default, which means the default output carries an error nobody measures. (sources/hemodynamic-hf-pht-aha-2026, rating: very high)
• The mid-thoracic zero corresponds to the left atrium only "in most patients". No alternative reference is defined for the patients in whom it does not, and the 0.8 mmHg per centimetre sensitivity means the wedge pressure absorbs that uncertainty more than any other measurement. (sources/rhc-hf-ehj-2025)
• Wedge pressure in atrial fibrillation remains approximate. The 130–160 ms rule is a convention, not a validation, and the escape route — direct LVEDP measurement — is not standardised across laboratories. (sources/hemodynamic-hf-pht-aha-2026)

Connections

• Part of concepts/Right-Heart-Catheterization — the parent overview
• concepts/RHC-Haemodynamic-Interpretation — what the measured numbers mean
• concepts/RHC-Clinical-Applications — the disease contexts these measurements serve
• concepts/Cardiac-Output-Measurement — method comparison and sources of output error
• concepts/Pulmonary-Hypertension — the diagnostic framework the pressures feed
• concepts/Right-Ventricular-Failure — the chamber the pressures describe
• concepts/Intracardiac-Shunts — the oximetry run and shunt calculation
• concepts/Primary-Mitral-Regurgitation — the lesion that produces large V-waves

Sources

• sources/rhc-hf-ehj-2025
• sources/hemodynamic-hf-pht-aha-2026
• sources/rhc-hf-jacchf-2024
• sources/co-indicator-anesthanalg-2010