Hemodynamics In The Cath Lab 2

HEMODYNAMICS IN THE CATH LAB

KOUSHIK R. REDDY, MD

• What is the cardiac output, SVR, PVR? • What is the AVA? • What is Carabello’s Sign? • What are the important Pitfalls?

PRESSURE MEASUREMENT • Reverend Stephen Hales measured the blood pressure of a horse by using a vertical glass tube in 1732. • Two important aspects: – Input Signal – Measuring devices

PRESSURE MEASUERMENT • The Input Signal: A complex periodic fluctuation in force per unit area. • Fundamental Frequency: Number of times the cycle occurs per second. • Fourier Analysis: A complex waveform is considered the mathematical summation of a series of sine waves of differing amplitudes and frequencies.

PRESSURE MEASUREMENT • The practical consequence of Fourier analysis is that, to record pressure accurately, a system must respond with equal amplitude for a given input throughout the range of frequencies contained within the pressure wave. • For example, the diacrotic notch contains a frequency of 10 Hz. If the system does not respond to 10Hz, the notch would be slurred or absent.

PRESSURE MEASUREMENT • MEASURING DEVICES Hurthle(1898):

PRESSURE MEASUREMENT • Properties of a Pressure Measuring Device • Sensitivity: Ratio of the amplitude of the recorded signal to the amplitude of the input signal. • Frequency Response: Ratio of output frequencies to input amplitude over a range of frequenciesof the input pressure wave. • Thus, sensitivity and frequency response are related reciprocally, and one can be obtained only by sacrificing the other.

• Properties of a Pressure Measuring Device • Natural Frequency: • Damping:

PRESSURE MEASUREMENT • Transforming Pressure Waves into Electrical Signal • Transducers: Use an electrical strain gauge and employ the principle of the Wheatstone bride. • Strain Gauge: Variable resistance transducer whose operation depends on the fact that when an electric wire is streched it’s resistance to the flow of current increases.

PRESSURE MEASUREMENT

PRESSURE MEASUREMENT

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

PRESSURE MEASUREMENT • Establishment of “Zero”

PRESSURE MEASUREMENT • Physiologic Characteristics of Pressure Waveforms • Reflected Waves:

PRESSURE MEASUREMENT

PRESSURE MEASUREMENT • Sources of Error and Artifact – Deterioration in frequency response – Catheter whip artifact – Catheter impact artifact – Systolic pressure amplification in the periphery – Errors in zero level and balancing

FLOW MEASUREMENT • Cardiac Output Fick’s Method Thermodilution Indicator Dilution • Vascular Resistance

FLOW MEASUREMENT • Fick’s Method: CO = Oxygen Consumption A – V O2 Diff Oxygen Consumption: Polarographic Paramagnetic Assumption (125mL/m2 or 110mL/m2)

FLOW MEASUREMENT

FLOW MEASUREMENT • Sources of Error – Fick’s principle assumes that a steady state exists – Determination of Oxygen saturation – Improper collection of mixed venous sample – Average error in O2 consumption ~ 6% – Average error in A – V O2 diff ~ 5% – Narrow AV diff more prone to introduce error than wide AV diff. – Fick’s method is more accurate in low cardiac output states. – Does O2 comsumption actually need to be Measured??

FLOW MEASUREMENT • Thermodilution Method

FLOW MEASUREMENT • Sources of Error with Thermodilution method. – Unreliable in the setting of significant TR. – Baseline temp. in the pulmonary artery usually shows distinct fluctuations. – Loss injected indicator’s (cold) temp. This can falsely overestimate the cardiac output in low floe states.

FLOW MEASUREMENT • Vascular Resistance Poiseuille’s Law:

FLOW MEASUREMENT • Estimation of Vascular Resistance in the Clinical Situation

FLOW MEASUREMENT • These equations yield resistance in arbitrary resistance units(ARU) or hybrid resistance units (HRU). Sometimes known as Woods Units since they were first introduced by Dr. Paul Wood. • Converted to metric system(dynes-sec-cm-5) by use of the conversion factor 80. • No particular advantage to either system. Most pediatric cardiologists use ARU and adult cardiologists use SI Units.

FLOW MEASUREMENT

SHUNT DETECTION AND QUANTIFICATION

SHUNT DETECTION AND QUANTIFICATION • Calculation of Pulmonary Blood Flow (Qp) • 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 shunt(100%O2, ECHO, Dye) If there is a R to L shunt use an assumedvalue of 98%. If the art desaturation is not due to R to L shunt, use the use the observed systemic art sat.

SHUNT DETECTION AND QUANTIFICATION • Calculation of Systemic Blood Flow(Qs)

SHUNT DETECTION AND QUANTIFICATION • Simplified Formula

SHUNT DETECTION AND QUANTIFICATION Limitations of Oxymetry Method • Absence of steady state. • Small shunts are not consistently detected. • O2 content varies with hemoglobin concentration. • Inc right sided sats in high flow states can be mistaken for L to R shunt.

SHUNT DETECTION AND QUANTIFICATION

CALCULATION OF STENOTIC VALVE AREA • As valvular stenosis develops, the valve orrifice produces progressively grater resistance to flow, resulting in a pressure drop(gradient) • Gorlin Formula:

CALCULATION OF STENOTIC VALVE AREA • Flow = CO/DFP or SEP

CALCULATION OF STENOTIC VALVE AREA • Mitral Valve Area: • A constant of 0.85 was derived after comparing calculated valve area to actual valve areas.

CALCULATION OF STENOTIC VALVE AREA

CALCULATION OF STENOTIC VALVE AREA Pitfalls • Wedge tracing: – Mean wedge should be lower than the mean PA pressure – Wedge sat should be equal to art sat or at least > 95%

CALCULATION OF STENOTIC VALVE AREA Alignment Mismatch • The A and V waves in an optimally damped PCW tracing are delayed typically by 50 to 70 msec compared with a simultaneous left atrail tracing.