Factors influencing the character of the pulmonary arterial wedge pressure

Accurate measurement of the transmitral gradient in patients with mitral stenosis: a simultaneous catheterization and Doppler echocardiographic study

OBJECTIVES

This study compared the accuracy of Doppler echocardiography with that of conventional cardiac catheterization in the measurement of transmitral gradients in patients with mitral stenosis.

BACKGROUND

Simultaneous measurement of left atrial and left ventricular pressures is the most accurate method for determination of the mean mitral valve gradient in patients with mitral stenosis. Because of the inherent risks of transseptal catheterization, pulmonary capillary wedge pressure has been used in many invasive laboratories for determination of the mean mitral valve gradient. Recent studies have observed significant errors when pulmonary capillary wedge pressure was used for these measurements. Doppler echocardiography provides a noninvasive alternative for measurement of the transmitral gradient, but its relative accuracy has remained unclear.

METHODS

Seventeen patients with mitral stenosis who underwent transseptal cardiac catheterization had simultaneous measurement of 1) transmitral gradient by direct left atrial and left ventricular pressures, 2) transmitral gradient by pulmonary capillary wedge and left ventricular pressures, and 3) transmitral gradient by Doppler echocardiography.

RESULTS

Transmitral gradient measured by pulmonary capillary wedge and left ventricular pressures significantly overestimated the gradient obtained by direct measurement of left atrial pressure, with a mean (+/- SD) difference of 3.3 +/- 3.5 mm Hg (or 53%). Correcting the pulmonary capillary wedge pressure for the phase shift resulted in better correlation, but a consistent overestimation still remained, with a mean difference of 2.5 +/- 2.9 mm Hg (or 43%). The best correlation with the smallest variability was comparison of the Doppler-derived mean gradient with the gradient from direct measurement of left atrial and left ventricular pressures, with a mean difference of 0.2 +/- 1.2 mm Hg.

CONCLUSIONS

Compared with the transmitral gradient obtained by direct measurement of left atrial and left ventricular pressures, the Doppler-derived gradient is more accurate than that obtained by conventional cardiac catheterization and should be considered the reference standard.

Interpretation of cardiac pathophysiology from pressure waveform analysis: the left-sided V wave

The left-sided V wave is dependent on both left atrial and ventricular pressure/volume filling relationship. The cardiac rhythm and timing of atrial systole also influences the V wave. The morphology of the V wave can reflect the severity of mitral regurgitation with stenosis, but valve areas in this setting may be better assessed by a pressure half-time method. Finally, as queried in our first patient example, V wave alternans is a reflection of left ventricular pressure alternans in a failing heart. Other signs of poor left ventricular function in Figure 1 also included an elevated minimal diastolic pressure and markedly elevated left ventricular end diastolic pressure. Hemodynamic findings of poor left ventricular function will be addressed in detail in a later "Rounds."

Beyond the wedge: clinical physiology and the Swan-Ganz catheter

The Swan-Ganz catheter was introduced into general clinical medicine in 1970 and quickly gained widespread use in the management of critically ill patients. The device offers highly sophisticated physiologic information; however, in many instances, only the wedge pressure and the cardiac output are utilized when managing acutely ill patients. The purpose of this review is to illustrate and explain the array of physiologic data available from the Swan-Ganz catheter in most circumstances. A basic understanding of the information that can be obtained with the Swan-Ganz catheter is quite useful in the diagnosis and management of a variety of cardiovascular disorders. In addition, the Swan-Ganz catheter can be a helpful tool for teaching cardiovascular pathophysiology.

Underestimation of prosthetic mitral valve areas: role of transseptal catheterization in avoiding unnecessary repeat mitral valve surgery

In patients with symptoms of heart failure after mitral valve replacement, identification of a stenosed prosthesis may be difficult. Twelve such patients were evaluated, presenting at a mean of 8.4 years after mitral valve replacement (four mechanical, eight porcine). Transvalvular pressure gradients were obtained using both indirect (pulmonary capillary wedge) and direct (transseptal catheterization) measurements of left atrial pressure. In all 12 patients, the diastolic gradient across the prosthetic valve was overestimated when pulmonary wedge rather than transseptal measurements were used. Calculated mitral valve prosthetic area was underestimated by the pulmonary wedge determinations. These findings may be caused by either the phase delay of the pulmonary wedge V wave relative to the transseptal V wave, resulting in a higher diastolic mean left atrial pressure, or the faulty wedge determinations in the setting of pulmonary hypertension, or both. In patients being considered for repeat mitral valve replacement because of prosthetic valve stenosis, transseptal catheterization allows for more accurate determination of prosthetic valve area and more accurately defines the need for repeat mitral valve surgery.

The value of left parasternal impulse recordings in the assessment of mitral regurgitation

Left parasternal cardiograms were recorded at the fifth intercostal space in 30 patients with mitral regurgitation. Early systolic outward movements (E), late systolic outward movements (LOM), and the ratio of the LOM area to the total area occupied by the left parasternal cardiogram (LPC area) were examined. Thirteen patients had pure mitral regurgitation due to ruptured chordae tendineae (ten patients) or "floppy mitral valve" (three patients). In these patients LOM/E correlated significantly with the regurgitation volume determined by the difference between angiographic and Fick stroke volumes, ( r = 0.93, P < 0.01), and with the height of the "v" wave in the pulmonary artery wedge pressure tracings ( r = 0.79; P < 0.01). Simultaneous recordings of left parasternal movements and pulmonary wedge pressures in eight patients in this group showed a close relationship between LOM and "v" waves.

Fourteen patients had rheumatic heart disease and mitral regurgitation associated with mitral stenosis of varying degrees of severity. In this group there was no significant correlation between LOM/E or LOM area/LPC area and the regurgitation volume or the height of the "v" wave. Of three patients who had congenital atrial septal defect in addition to mitral regurgitation, none had prominent LOM in the left parasternal cardiogram.

This study suggests that if mitral stenosis and atrial septal defect can be excluded on clinical evidence, the left parasternal cardiogram may be used to obtain a noninvasive assessment of the severity of mitral regurgitation, particularly in patients with recent onset of the disease.

Influence of Catheter Tip Position on Pulmonary Wedge Pressures

Pulmonary artery wedge pressures and wedge pulmonary arteriograms were obtained in 68 patients with either mitral stenosis, congenital heart disease, or no demonstrable heart disease. The arteriogram defines five catheter tip positions in the wedged artery. Tip positions unfavorable for left atrial pressure transmission occurred in 20 of the 68 trials and accounted for 19 of the 31 unsatisfactory tracings. Favorable tip positions were found in 48 instances and resulted in 36 phasic tracings. Unsatisfactory tracings in patients with pulmonary hypertension and congenital heart disease are shown to result primarily from unfavorable catheter tip positions. In these patients structural changes in the larger pulmonary arteries may prevent proper wedging. Increased left atrial pressure assures transmission of a cyclic left atrial pulse to a properly impacted catheter regardless of the degree of associated pulmonary hypertension. It is concluded that the fortuitous position assumed by the catheter tip in the wedged artery and the level of the left atrial pressure are factors of major importance in the satisfactory recording of the left atrial pulse curve by the wedged catheter.