Hemodynamic Data and Basic Electrocardiography

3 Hemodynamic Data and Basic Electrocardiography

Pressure Waves in the Heart

Blood within the heart or vessels exerts pressure. A pressure wave is created by cardiac muscular contraction and is transmitted from the vessel or chamber along a closed, fluid-filled column (catheter) to a pressure transducer, which converts the mechanical pressure to an electrical signal that is displayed on a video monitor. Cardiac pressure waveforms are cyclical, repeating the pressure change from the onset of one cardiac contraction (systole) to the onset of the next contraction. The complete description of the physiology of heart function is beyond the scope of this book, but an examination of the diagram of the cardiac cycle and corresponding pressures (Figs. 3-1 and 3-2) provides an understanding of basic hemodynamics in the cardiac catheterization laboratory.

The collection of hemodynamic data is an integral part of every catheterization protocol. Even complex hemodynamic data recording can be accomplished accurately and rapidly if an efficient and consistently used method is established in the laboratory. One measurement sequence used in our laboratory (Tables 3-1, 3-2, and 3-3) is an example of one method. This sequence facilitates simultaneous pressure measurements across the heart, concentrating on the aortic (Ao) and mitral valves, which are the most commonly affected by disease. Of all hemodynamic questions, 90% can be answered by examining data collected in this way. As with most brief formulas this technique is not all-inclusive. Different hemodynamic measurements for specific clinical situations are necessary. Specific examples are included in the case studies.

Table 3-1 Right-Sided Heart Catheterization Protocol

Only 1 to 2 drops of heparin should be aspirated and flushed out of 1- to 3-ml heparinized syringes.

Table 3-2 Left-Sided Heart Catheterization Protocol

Right-sided heart hemodynamic studies often precede left-sided heart studies. Simultaneous pressures of the left and right sides of the heart provide the most precise and accurate information.

100 mm/sec sweep speed if aortic valve gradient present.

Table 3-3 Combined Hemodynamic Measurements of the Left and Right Sides of the Heart

Begin studies after right-sided heart catheterization is completed with pulmonary capillary wedge (PCW) tracing ready and left ventricular (LV) protocol completed with pigtail catheter in left ventricle before LV pullback.

The routine collection of hemodynamic data from the right and left sides of the heart with appropriate sampling of blood for oxygen saturations and CO measurements can be accomplished in less than 30 minutes. CO by the thermodilution technique is routine. The Fick CO method using a measured or assumed oxygen consumption calculation is often used for valvular lesions. Arterial, vena caval, right atrial (RA), and pulmonary artery (PA) oxygen saturations are collected routinely throughout the right and left sides of the heart for intracardiac shunt identification.

Right- and Left-Sided Heart Catheterization

The protocol used during right-sided heart catheterization is summarized in Table 3-1. Right-sided heart catheterization is performed for specific indications. Right-sided heart catheterization is indicated for patients with a history of dyspnea, valvular heart disease, or intracardiac shunts. Patients with a history of pulmonary edema occurring on a previous hospital admission often have only dyspnea with no objective evidence of left ventricular (LV) dysfunction (e.g., chest film, echocardiography). Dyspnea caused by lung disease cannot be differentiated from that caused by pulmonary hypertension or LV dysfunction.

Complications of Right-Sided Heart Catheterization

The most common problem during right-sided heart catheterization is arrhythmia resulting from stimulation of the right ventricular (RV) outflow tract, which may result in ventricular tachycardia (VT), atrioventricular (AV) block or, rarely, right bundle-branch block (Table 3-4). Significant but transient ventricular arrhythmias occur in 30% to 60% of patients who undergo right-sided heart catheterization and are self-limited and do not require treatment. The arrhythmia is terminated when the catheter is readjusted. Sustained ventricular arrhythmias have been reported, especially in unstable patients or patients with electrolyte imbalance, acidosis, or concurrent myocardial ischemia. The prophylactic use of lidocaine is not necessary. In patients with left bundle-branch block, a temporary pacemaker may be necessary if right bundle-branch block occurs during right-sided heart catheterization.

Table 3-4 Cardiac Shunt Locations

Location Earliest Step-Up Location (for Left-to-Right Shunts)
Atrial Septal Defects  
Primum (low) RA, RV
Secundum (mid) RA
Sinus venosus (high) RA
Partial anomalous pulmonary venous return (pulmonary veins entering right atrium) RA
Ventricular Septal Defects  
Membranous (high) RV
Muscular (mid) RV
Apical (low) RV
Aorticopulmonary window (connection of aorta to pulmonary artery) PA
Patent ductus arteriosus (normally closed Ao-PA connection at birth) PA

Ao, Aortic; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

Use of Pulmonary Wedge Pressure

The pulmonary capillary wedge (PCW) pressure closely approximates left atrial (LA) pressure reflecting the filling pressures of the left ventricle. PCW pressure overestimates LA pressure in patients with acute respiratory failure, chronic obstructive pulmonary disease with pulmonary hypertension, pulmonary veno-occlusive disease (e.g., pulmonary vein stenosis after atrial fibrillation [AF] ablation), or LV failure with volume overload. Reported discrepancies between LA and PCW pressure may be caused in part by different types of catheters: Balloon-tipped flotation catheters are soft with small lumens; transseptal pressure catheters (e.g., Brockenbrough or Mullins-type sheath) are stiff with large lumens. In most patients, PCW pressure is sufficient to assess LV filling pressure. In patients with mitral valvular disease or mitral valve prostheses, a significant error may be introduced by using a balloon-tipped flotation catheter for PCW pressure assessment. Transseptal LA catheterization should be considered in these cases.

Rules for obtaining an accurate PCW pressure that agrees with LA pressure are as follows:

Left-Sided Heart Catheterization

The protocol for left-sided heart catheterization is summarized in Table 3-2. Indications for left-sided heart catheterization are summarized in Chapter 1. A combined right-side and left-side heart protocol is a precise and complete method of addressing the most common hemodynamic problems in the catheterization laboratory (see Table 3-3).

Computations for Hemodynamic Measurements

When the hemodynamic data have been obtained, computations are made to quantify cardiac function. In this section only the most common computations and standard formulas are provided. These computations provide measurement of cardiac work, flow resistance, valve areas, and shunts. Specific derivations and applications of these formulas can be found elsewhere.


Oxygen consumption is best measured from a metabolic “hood” (this device is no longer widely available); it is more commonly estimated as 3 ml O2/kg or 125 ml/min/m2. Arteriovenous oxygen (AVO2) difference is calculated from arterial – mixed venous (PA) O2 content, where O2 content = saturation × 1.36 × hemoglobin.

For example, if the arterial saturation is 95%, then the O2 content = 0.95 × 1.36 × 13.0 g = 16.7 ml, PA saturation is 65%, and O2 consumption is 210 ml/min (70 kg × 3ml/kg) or measured value, and CO would be determined as follows:



where CO = cardiac output; BSA = body surface area.


where HR = heart rate.






Resistance calculations follow the form of Ohm’s law, where


R = resistance; Δp = mean pressure differential across the vascular bed; image = blood flow. Resistance units (mm Hg/L/min) are also called Hybrid resistance units or Wood units. To convert Wood units to metric resistance (dynes × s × cm–5), multiply by 80.

Computations of Valve Areas from Pressure Gradients and Cardiac Output

A pressure gradient is the pressure difference across an area of valvular or vascular obstruction, such as a stenosis or an occlusion or narrowed valve. Figure 3-3 is a diagram of a coronary stenosis with higher pressure proximal to the stenosis and lower pressure beyond the stenosis. The same principle applies for heart valves with higher pressure proximal to the stenotic valve and lower pressure distal to it. There are several methods used to measure transvalvular gradients.

Techniques to measure LV-Ao pressure gradients include the following in order of least to most accurate:

All pressure gradients are affected by a number of physiologic, anatomic, and artifactual variables. Physiologic variables include (1) rate of blood flow (e.g., CO, coronary blood flow), (2) resistance to flow, and (3) proximal chamber pressure and compliance. Anatomic variables include (1) shape and length of valve orifice, (2) tortuosities of the vessels (for arterial stenosis); folding of coronary artery by guidewire (i.e., pseudostenosis), and(3) multiple or serial lesions (for cardiac valves and arterial stenosis).

Artifactual variables include

Examples of Aortic and Mitral Valve Area Calculations

Most modern physiologic recording systems use computer-generated waveforms and gradient producing valve areas automatically. When using femoral artery and LV pressure, time shifting the femoral artery back to match upstroke of the left ventricle will under-estimate the true Ao valve gradient (Fig 3-4). When calculating from the formula, CO should be converted to milliliters per minute, not liters per minute. When computing flow, the ejection period and filling period are converted to fractions of the period in seconds.

Data obtained at catheterization for Ao stenosis (Fig. 3-5):






Notes on the Ao Valve Gradient

The mean pressure gradient is the area of the superimposed Ao and LV pressure tracings. Peak-to-peak pressure gradients are easily seen and are often used as an estimate of the severity of stenosis. The peak-to-peak gradient is not equivalent to mean gradient for mild and moderate stenosis but is often close to mean gradient for severe stenosis.

The delay in pressure transmission and pressure wave reflection from the proximal aorta to the femoral artery artificially increases the mean gradient. If matched to the upstroke of the left ventricle, femoral pressure overshoot (amplification) reduces the true gradient. In patients with low gradients (i.e., <35 mm Hg), more accurate valve areas were obtained with unshifted LV-Ao pressure tracings (Fig. 3-4; Folland et al). Optimally a second catheter can be positioned directly above the Ao valve to reduce transmission delay and femoral pressure amplification. A long (>30 cm) arterial sheath can be used. Transseptal cardiac catheterization can also be performed to obtain direct LV pressure (Fig. 3-5 shows LV-Ao pressure measure from central Ao catheter without delay in the upstroke of Ao pressure).

Simplified formulas provide quick in-laboratory determinations of Ao valve area. Ao valve area can be accurately estimated as CO divided by the square root of the LV-Ao peak-to-peak pressure difference.



Note: The quick formulas for valve area differ from the Gorlin formula by 18 ± 13% in patients with bradycardia (<65 beats/min) or tachycardia (>100 beats/min). The Gorlin equation at low-flow states overestimates the severity of valve stenosis. In low-flow states (CO <2.5 L/min), the Gorlin formula should be modified to use the mean transvalvular gradient with new empirically derived constants.

Use of Valve Resistance for Aortic Stenosis

Valve resistance, a measure of valve obstruction, although not commonly computed has been shown to have clinical value. Valve resistance has not been used because the units of dynes − second − cm−5 were not well related to clinical outcomes.

Although they have obvious strengths, valve area measurements have practical and theoretical limitations such as three-dimensional (3D) geometric influences on flow, using blood as nonviscous fluid, neglecting turbulence and blood viscosity, and assuming that blood flow is gravity driven rather than pulsatile as in the arterial system.

Valve areas of less than 0.7 cm2 are almost always associated with an important clinical syndrome, and areas of greater than 1.1 cm2 are usually not associated with significant symptoms, but areas between these two measurements are in a gray zone. One of the most common clinical situations is found in a patient with a valve area of 0.9 to 1.0 cm2, a low transvalvular pressure gradient, low CO, and poor LV function. There is uncertainty regarding the outcome after valve replacement, as well as a high mortality rate if ventricular function does not improve after surgery.

Valve resistance is calculated using the same variables for valve area measurement. In contrast to valve area, the mean pressure gradient is considered to be a linear variable rather than taken as a square root term. The contribution of pressure gradient to the magnitude of valve resistance is greater. Resistance has also been shown to be more constant than valve area under conditions of changing CO. Figure 3-6 shows resistance and area calculated in a group of patients before and after balloon Ao valve dilation. Resistance rises sharply above a valve area of 0.7 cm2. The shoulder of this curve is 0.7 to 1.1 cm2, which is the common area of indeterminate significance of Gorlin Ao valve area. Some patients in this gray zone tend to have higher valve resistance than others. It has been shown in this setting that patients with resistance greater than 250 dynes − sec − cm−5 are more likely to have significant obstruction than patients with resistance less than 200 dynes − sec − cm−5. There is also a gray zone in using this index, and some patients may have resistance less than 250 dynes − sec − cm−5 despite a planar valve area of 0.7 to 0.8 cm2.

Resistance is a complementary index, not a replacement for valve area. Valve resistance is not expected to remain consistent. As with peripheral resistance, valve resistance is interpreted in the context of the clinical conditions under which it is measured. A peripheral resistance of 1000 dynes − sec − cm−5 has a different significance in a patient with presumed sepsis than it does in a patient with LV failure. Similarly, we can expect valve resistance to vary as CO changes.

Catheter Selection for Aortic Stenosis

Initial catheter selection is a matter of operator choice and experience. The pigtail ventriculography catheter is a good initial choice in most cases. The operator crosses the Ao valve with a 0.038-inch, straight-tipped safety guidewire, extending the wire and straightening the pigtail with a slight angled bend. The operator should direct the wire into the area of highest turbulence as detected by jet impaction on the wire, and note the movement as visualized on the fluoroscopy monitor. Manipulation of the wire and catheter allows positioning of the wire in various directions needed to cross the valve. Advancing the pigtail over the wire and, in most cases, rapidly positioning the catheter for ventriculography and hemodynamic studies is a simple operation. When this method is successful it is a one-step procedure, and for this reason the pigtail catheter is a logical first choice. Other catheter choices for crossing the Ao valve include the left and, occasionally, right Amplatz catheter, right Judkins catheter, multipurpose catheter, and specially designed catheters. When the operator must use an alternative catheter, the left and right Judkins catheters can complete coronary angiography between catheter exchanges. All but the pigtail catheter are generally unsuitable for LV angiography. It should not require more than 15 minutes to cross the stenotic Ao valve, and if great difficulty is encountered, a transseptal approach should be considered early in the procedure.

When Do You Need to Cross the Aortic Valve for Hemodynamic Assessment?

The Class I indications (experts agree procedure indicated) are as follows:

The Class III indications not to cross the Ao valve during cardiac catheterization (experts agree procedure provides no benefit or may be harmful) are as follows:

It is my view that if the echocardiogram can provide precise, accurate, reproducible, high-quality, and high-confidence information, then crossing Ao valve is relatively superfluous. This would also apply for any routine catheterization because left ventricular function can readily be assessed by echo, and the importance of left ventricular end-diastolic pressure (LVEDP) has minimal contribution to the decision making for most patients. However, in the patient with Ao stenosis in whom there is a question about the adequacy of the noninvasive testing, certainly retrograde cannulation of the Ao valve is important and for any patient with discordant findings, a true transvalvular gradient is the standard of care. The decision for Ao valve replacement based on echocardiography alone has been questioned by some with an experience in which the echocardiogram has registered mitral regurgitation and the finding has been confused with Ao stenosis. Thus the decision remains patient-specific, echocardiographer-specific, and hemodynamic operator–specific as to whether one should cross the valve or not. A really good echocardiogram will obviate the need to cross the stenotic Ao valve.

Data from Catheterization Laboratory for Calculation of Mitral Valve Area

Figure 3-7 is a hemodynamic tracing to calculate mitral valve area.

Step 1: Planimeter 5 LV-PCW areas (10 if in atrial fibrillation).

Area = 9.46 cm2

Step 2: Measure diastolic filling period (DFP).


Step 3: Convert planimetered area to mean diastolic pressure gradient.


Step 4: Compute mitral valve flow.

For the mitral gradient, similar to Ao valve areas, DFP is in centimeters at this point owing to scale factor.


Step 5: Compute mitral valve area (MVA).


Simplified Mitral Valve Gradient Calculation by Cui et al

Cui simplified the estimation of the mitral valve gradient (MVG) and thus simplified the calculation of mitral valve area from the hemodynamic tracings. Because the mean MVG is the pressure difference between the mean left atrial pressure (MLAP) and mean left ventricular pressure during diastole (MLVP) (i.e., MLVG = MLAP – MLVP), the computation of the mean MVG is simply knowing the MLVP. The MLAP is easily obtained from the electronically meaned LA signal on the hemodynamic recorder. The area under the LV pressure during diastole is roughly a triangle with the three corners formed from the intersections of the diastolic filling period (DFP) starting and ending points (mitral valve closure and opening) marking the vertical lines intersecting with the LV pressure line (rising diagonally across diastole, see Figure 3-9). This triangular area can be estimated from the rectangular area LVEDP × DFP divided by 2. Thus the MLVP is equal to the LVEDP/2. From this key calculation, the mean valve gradient is therefore simplified as


There is strong correspondence between the mitral valve areas calculated by the Gorlin and Hakki formulas, both before and after mitral balloon valvuloplasty with an error of estimates at 1.6 mm Hg. The Cui MVG slightly overestimated MVG before but not after mitral valvuloplasty. Hakki significantly under-estimated MVGs after mitral balloon valvuloplasty. Unlike Hakki, the Cui MVG was not affected by mitral regurgitation, Ao insufficiency, atrial fibrillation, or heart rate.

Although simple, the Cui MVG still has potential problems. Heart rate changes will change the shape of the triangular area under the LV pressure curve, and thus tachycardia may cause a potential overestimation of valve severity. There is one very interesting advantage for this simplified method. The MVG can be estimated easily from a pressure pullback from left ventricle to the left atrium without necessarily making simultaneous two-chamber tracings. Mitral valve area could be calculated without entering the left ventricle.

Pulmonic Valve Stenosis

A pulmonary valvular stenosis gradient (Fig. 3-10) can be obtained by catheter “pullback,” continuously measuring pressure during catheter withdrawal across the stenotic valve. Two catheters, multiple-lumen balloon-tipped catheters, or double-lumen Cournand catheters are more precise, however, and can record simultaneous PA and RV pressures in the manner used for Ao valve stenosis. There is no validated formula for pulmonary valve area. Prognostic data are based on RV pressure and gradient alone.

Measurement of Cardiac Output

In the cardiac catheterization laboratory, CO is determined by one of two techniques: (1) measurement of oxygen consumption (Fick technique) or (2) indicator dilution technique (thermodilution using a PA catheter).

Jun 5, 2016 | Posted by in CARDIAC SURGERY | Comments Off on Hemodynamic Data and Basic Electrocardiography

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