Hemodynamics in the Cath Lab 2

HEMODYNAMICS IN THE CATH LABHEMODYNAMICS IN THE CATH LAB

KOUSHIK R. REDDY, MDKOUSHIK R. REDDY, MD

• What is the cardiac output, SVR, PVR?What is the cardiac output, SVR, PVR?

• What is the AVA?What is the AVA?

• What is Carabello’s Sign?What is Carabello’s Sign?

• What are the important Pitfalls?What are the important Pitfalls?

PRESSURE MEASUREMENTPRESSURE MEASUREMENT

• Reverend Stephen Hales measured the blood Reverend Stephen Hales measured the blood pressure of a horse by using a vertical glass tube in pressure of a horse by using a vertical glass tube in 1732.1732.

• Two important aspects:Two important aspects:– Input SignalInput Signal

– Measuring devicesMeasuring devices

PRESSURE MEASUERMENTPRESSURE MEASUERMENT

• The Input Signal: The Input Signal: A complex periodic fluctuation in A complex periodic fluctuation in force per unit area.force per unit area.

• Fundamental Frequency:Fundamental Frequency: Number of times the Number of times the cycle occurs per second. cycle occurs per second.

• Fourier Analysis: Fourier Analysis: A complex waveform is A complex waveform is considered the mathematical summation of a series considered the mathematical summation of a series of sine waves of differing amplitudes and of sine waves of differing amplitudes and frequencies.frequencies.


• The practical consequence of Fourier analysis is The practical consequence of Fourier analysis is that, to record pressure accurately, a system must that, to record pressure accurately, a system must respond with equal amplitude for a given input respond with equal amplitude for a given input throughout the range of frequencies contained throughout the range of frequencies contained within the pressure wave.within the pressure wave.

• For example, the diacrotic notch contains a For example, the diacrotic notch contains a frequency of 10 Hz. If the system does not respond frequency of 10 Hz. If the system does not respond to 10Hz, the notch would be slurred or absent.to 10Hz, the notch would be slurred or absent.


• MEASURING DEVICESMEASURING DEVICES

Hurthle(1898): Hurthle(1898):


• Properties of a Pressure Measuring DeviceProperties of a Pressure Measuring Device

• Sensitivity:Sensitivity: Ratio of the amplitude of the recorded Ratio of the amplitude of the recorded signal to the amplitude of the input signal.signal to the amplitude of the input signal.

• Frequency Response: Frequency Response: Ratio of output frequencies Ratio of output frequencies to input amplitude over a range of frequenciesof the to input amplitude over a range of frequenciesof the input pressure wave.input pressure wave.

• Thus, sensitivity and frequency response are related Thus, sensitivity and frequency response are related reciprocally, and one can be obtained only by reciprocally, and one can be obtained only by sacrificing the other.sacrificing the other.

• Properties of a Pressure Measuring DeviceProperties of a Pressure Measuring Device

• Natural Frequency:Natural Frequency:

• Damping:Damping:


• Transforming Pressure Waves into Electrical Transforming Pressure Waves into Electrical SignalSignal

• Transducers: Transducers: Use an electrical strain gauge and Use an electrical strain gauge and employ the principle of the Wheatstone bride.employ the principle of the Wheatstone bride.

• Strain Gauge: Strain Gauge: Variable resistance transducer Variable resistance transducer whose operation depends on the fact that when an whose operation depends on the fact that when an electric wire is streched it’s resistance to the flow of electric wire is streched it’s resistance to the flow of current increases.current increases.


• Balancing a Transducer:Balancing a Transducer: Interpolating a variable Interpolating a variable resistance across the output of a wheatstone bridge resistance across the output of a wheatstone bridge so that atmospheric pressure at the “zero level” so that atmospheric pressure at the “zero level” induces an arbitrary voltage output on the induces an arbitrary voltage output on the moniter(I.e., a voltage that positions the transducer moniter(I.e., a voltage that positions the transducer output on the ascilloscope pressure baseline)output on the ascilloscope pressure baseline)


• Establishment of “Zero”Establishment of “Zero”


• Physiologic Characteristics of Pressure WaveformsPhysiologic Characteristics of Pressure Waveforms

• Reflected Waves:Reflected Waves:


• Sources of Error and ArtifactSources of Error and Artifact

– Deterioration in frequency responseDeterioration in frequency response

– Catheter whip artifactCatheter whip artifact

– Catheter impact artifactCatheter impact artifact

– Systolic pressure amplification in the peripherySystolic pressure amplification in the periphery

– Errors in zero level and balancingErrors in zero level and balancing

FLOW MEASUREMENTFLOW MEASUREMENT

• Cardiac OutputCardiac Output

Fick’s MethodFick’s Method

ThermodilutionThermodilution

Indicator DilutionIndicator Dilution

• Vascular ResistanceVascular Resistance


• Fick’s Method:Fick’s Method:

CO = CO = Oxygen ConsumptionOxygen Consumption

A – V O2 DiffA – V O2 Diff

Oxygen Consumption:Oxygen Consumption:

PolarographicPolarographic

ParamagneticParamagnetic

Assumption (125mL/m2 or 110mL/m2)Assumption (125mL/m2 or 110mL/m2)


• Sources of ErrorSources of Error– Fick’s principle assumes that a steady state existsFick’s principle assumes that a steady state exists

– Determination of Oxygen saturationDetermination of Oxygen saturation

– Improper collection of mixed venous sampleImproper collection of mixed venous sample

– Average error in O2 consumption ~ 6%Average error in O2 consumption ~ 6%

– Average error in A – V O2 diff ~ 5%Average error in A – V O2 diff ~ 5%

– Narrow AV diff more prone to introduce error than wide AV Narrow AV diff more prone to introduce error than wide AV diff. diff.

– Fick’s method is more accurate in low cardiac output states.Fick’s method is more accurate in low cardiac output states.

– Does O2 comsumption actually need to be Measured??Does O2 comsumption actually need to be Measured??


• Thermodilution MethodThermodilution Method


• Sources of Error with Thermodilution method.Sources of Error with Thermodilution method.

– Unreliable in the setting of significant TR.Unreliable in the setting of significant TR.

– Baseline temp. in the pulmonary artery usually shows Baseline temp. in the pulmonary artery usually shows distinct fluctuations.distinct fluctuations.

– Loss injected indicator’s (cold) temp. This can falsely Loss injected indicator’s (cold) temp. This can falsely overestimate the cardiac output in low floe states.overestimate the cardiac output in low floe states.


• Vascular ResistanceVascular Resistance

Poiseuille’s Law: Poiseuille’s Law:


• Estimation of Vascular Resistance in the Clinical Estimation of Vascular Resistance in the Clinical SituationSituation


• These equations yield resistance in arbitrary These equations yield resistance in arbitrary resistance units(ARU) or hybrid resistance units resistance units(ARU) or hybrid resistance units (HRU). Sometimes known as Woods Units since (HRU). Sometimes known as Woods Units since they were first introduced by Dr. Paul Wood.they were first introduced by Dr. Paul Wood.

• Converted to metric system(dynes-sec-cm-5) by use Converted to metric system(dynes-sec-cm-5) by use of the conversion factor 80.of the conversion factor 80.

• No particular advantage to either system. Most No particular advantage to either system. Most pediatric cardiologists use ARU and adult pediatric cardiologists use ARU and adult cardiologists use SI Units.cardiologists use SI Units.

SHUNT DETECTION AND QUANTIFICATIONSHUNT DETECTION AND QUANTIFICATION


• Calculation of Pulmonary Blood Flow (Qp)Calculation of Pulmonary Blood Flow (Qp)

• If the pulm vein is not enterd SaO2 may be used, if it If the pulm vein is not enterd SaO2 may be used, if it is 95% or more. Is Sao2 is < 95%, first r/o R to L is 95% or more. Is Sao2 is < 95%, first r/o R to L shunt(100%O2, ECHO, Dye) If there is a R to L shunt(100%O2, ECHO, Dye) If there is a R to L shunt use an assumedvalue of 98%. If the art shunt use an assumedvalue of 98%. If the art desaturation is not due to R to L shunt, use the use desaturation is not due to R to L shunt, use the use the observed systemic art sat.the observed systemic art sat.

SHUNT DETECTION AND QUANTIFICATIONSHUNT DETECTION AND QUANTIFICATION• Calculation of Systemic Blood Calculation of Systemic Blood

Flow(Qs)Flow(Qs)


• Simplified FormulaSimplified Formula


Limitations of Oxymetry MethodLimitations of Oxymetry Method

• Absence of steady state.Absence of steady state.

• Small shunts are not consistently detected.Small shunts are not consistently detected.

• O2 content varies with hemoglobin concentration.O2 content varies with hemoglobin concentration.

• Inc right sided sats in high flow states can be Inc right sided sats in high flow states can be mistaken for L to R shunt.mistaken for L to R shunt.

CALCULATION OF STENOTIC VALVE AREACALCULATION OF STENOTIC VALVE AREA

• As valvular stenosis develops, the valve orrifice As valvular stenosis develops, the valve orrifice produces progressively grater resistance to flow, produces progressively grater resistance to flow, resulting in a pressure drop(gradient)resulting in a pressure drop(gradient)

• Gorlin Formula:Gorlin Formula:


• Flow = CO/DFP or SEP Flow = CO/DFP or SEP


• Mitral Valve Area:Mitral Valve Area:

• A constant of 0.85 was derived after comparing A constant of 0.85 was derived after comparing calculated valve area to actual valve areas.calculated valve area to actual valve areas.


PitfallsPitfalls

• Wedge tracing:Wedge tracing:– Mean wedge should be lower than the mean PA pressureMean wedge should be lower than the mean PA pressure

– Wedge sat should be equal to art sat or at least > 95%Wedge sat should be equal to art sat or at least > 95%


Alignment MismatchAlignment Mismatch

• The A and V waves in an optimally damped PCW The A and V waves in an optimally damped PCW tracing are delayed typically by 50 to 70 msec tracing are delayed typically by 50 to 70 msec compared with a simultaneous left atrail tracing.compared with a simultaneous left atrail tracing.

Hemodynamics in the Cath Lab 2

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