Background
Two-dimensional and Doppler-derived echocardiographic data on normal St. Jude Medical mechanical mitral valve prosthesis function have been reported but remain limited.
Methods
Comprehensive retrospective two-dimensional and Doppler echocardiographic assessment of 368 normal St. Jude Medical mechanical mitral valve prostheses was performed early after implantation. The early postimplantation hemodynamic profiles of 98 patients were compared with profiles obtained by follow-up transthoracic echocardiography performed <13 months after implantation.
Results
Using mean ± 2 SDs to define the normal distribution of values for Doppler-derived hemodynamic variables, the calculated normal ranges of values were as follows: mean gradient, 2 to 7 mm Hg; peak early mitral diastolic velocity (E velocity), 1.1 to 2.4 m/sec; time-velocity integral of the mitral valve prosthesis (TVI MVP ) 20 to 50 cm; ratio of the TVI MVP to the time-velocity integral of the left ventricular outflow tract (TVI LVOT ), 0.9 to 2.5; pressure half-time, 35 to 99 msec; and effective orifice area, 1.12 to 3.24 cm 2 . Patients with severe prosthesis-patient mismatch (ie, indexed effective orifice area ≤ 0.9 cm 2 /m 2 ) had significantly higher mean gradients, E velocity, TVI MVP , and TVI MVP /TVI LVOT . There was a trend for longer pressure half-times for patients with severe prosthesis-patient mismatch than for patients without severe prosthesis-patient mismatch, but none of these patients had pressure half-times > 130 msec. Among the 98 patients with follow-up transthoracic echocardiography <1 year after implantation, no significant differences were observed between early postimplantation findings and follow-up hemodynamic profiles.
Conclusions
This study establishes parameters (mean ± 2 SDs) defining the distribution of values for Doppler-derived hemodynamic data with normal St. Jude Medical mechanical mitral valve prostheses. Prostheses with hemodynamic values outside these parameters are likely dysfunctional; however, prosthesis dysfunction may be present even when hemodynamic values are within these ranges.
Two-dimensional (2D) echocardiography combined with Doppler is the noninvasive method of choice for the evaluation of prosthetic valve function. Recent recommendations from the American Society of Echocardiography (ASE) and the European Association of Echocardiography (EAE) specify that the Doppler-derived hemodynamic assessment of mitral prosthesis function should include peak early mitral diastolic velocity (E velocity), mean gradient (MG), pressure half-time (PHT), the time-velocity integral (TVI) of the mitral valve prosthesis (TVI MVP ), the ratio of the TVI MVP to the TVI of the left ventricular outflow tract (TVI LVOT ), effective orifice area (EOA) calculated by the continuity equation, and indexed EOA (IEOA) calculated by the continuity equation. Several reports from other institutions have examined Doppler-derived hemodynamic profiles of various sizes of normally functioning St. Jude Medical (SJM; St. Paul, MN) mechanical mitral valve prostheses, but the data from these studies are limited. A previous study from our own institution examined data for all the pertinent hemodynamic parameters but evaluated only 119 prostheses and included several older models of SJM prostheses in the study group.
The purpose of the current retrospective study was threefold: (1) to establish the range of normal values for all the important Doppler-derived hemodynamic parameters previously described in the medical literature for a large number of patients with normal SJM mechanical mitral valve prostheses, (2) to compare hemodynamic parameters of normal SJM mechanical mitral valve prostheses in patients with and without severe prosthesis-patient mismatch (PPM), and (3) to compare hemodynamic variable values for SJM mechanical mitral valve prostheses obtained in the early postoperative period to values obtained for the same prostheses 1 to 13 months postoperatively.
Methods
The study was approved by the Mayo Clinic Institutional Review Board. All study patients provided written informed consent to allow the use of their medical records for research purposes. No industry support was provided.
Patient Selection
From the cardiac surgical database of the Mayo Clinic (Rochester, MN), we identified 740 patients aged ≥ 18 years who underwent mitral valve replacement with SJM standard (model MECJ-502) mechanical mitral valve prostheses between January 1, 1993, and December 31, 2008. Of these 740 patients, nine with congenitally corrected transposition had replacement of their left-sided morphologic tricuspid valves, which is equivalent, from a hemodynamic standpoint, to mitral valve replacement. Three hundred seventy-two patients met the prespecified exclusion criteria: 30 died within 30 days of surgery, 105 did not undergo intraoperative transesophageal echocardiography (TEE), 105 did not undergo transthoracic echocardiography (TTE) within 30 days of surgery, one had signs of impaired leaflet excursion on postoperative TTE, three had evidence of considerable mitral valve prosthesis or periprosthetic regurgitation on postoperative TTE, 43 had heart rates ≥ 100 beats/min, nine were on vasopressors at the time of postoperative TTE, and 76 had inadequate images for obtaining accurate and complete Doppler data on postoperative TTE. The remaining 368 patients constituted the study population.
All prostheses in the study population appeared to be functioning normally as determined by physical examination and by 2D and color flow imaging both on intraoperative TEE and on TTE <30 days after surgery. No patient had greater than mild mitral transprosthetic or periprosthetic regurgitation or aortic regurgitation on intraoperative TEE or postoperative TTE.
Echocardiographic Data
Left ventricular ejection fraction (LVEF) was obtained using either M-mode or a modification of the 2D Quinones method. If these measurements were deemed insufficient, LVEF was estimated visually. The presence and severity of aortic regurgitation and mitral transprosthetic or periprosthetic regurgitation were assessed.
Doppler data were obtained either from videotapes using the DigiView Image Management and Reporting System release 3.6.3 (Digisonics Inc., Houston, TX) or from digital images using ProSolv software (ProSolv CardioVascular, Indianapolis, IN) for offline analysis by one investigator (L.A.B.).
The standard practice in our echocardiography laboratory is to average three cardiac cycles of the left-heart Doppler measurements if patients are in sinus rhythm and at least five cardiac cycles if patients have atrial fibrillation or another irregular rhythm. For patients with irregular rhythms, attempts are made to use periods of physiologic heart rate and to match the five cardiac cycle lengths for each parameter. The number of cardiac cycles and individual measurements are approved by the supervising echocardiography consultant before inclusion in the final report.
The prosthesis EOA was calculated using the continuity equation (EOA = stroke volume [SV]/TVI MVP ). Continuous-wave Doppler velocity spectra were measured for MG, E velocity, PHT, and TVI MVP using image-guided and nonimaging probes. To establish values for defining the distribution of hemodynamic variables for patients with normal SJM mechanical mitral valve prostheses, we calculated the mean ± 2 SDs for MG, E velocity, TVI MVP , TVI MVP /TVI LVOT , PHT, EOA, and IEOA.
SV was calculated as the product of left ventricular outflow tract (LVOT) area and the TVI LVOT measured on pulsed-wave Doppler. The prosthesis performance index (PPI) was calculated as the ratio of the EOA derived by the continuity equation to the geometric orifice area (GOA) provided by the manufacturer (SJM): 2.55 cm 2 for the 23-mm valve, 3.09 cm 2 for the 25-mm valve, 3.67 cm 2 for the 27-mm valve, 4.41 cm 2 for the 29-mm valve, and 5.18 cm 2 for the 31-mm and 33-mm valves. Because GOA values are identical for the 31-mm and 33-mm SJM mitral valves, we performed a subgroup analysis of these two valve sizes to determine whether their hemodynamic values varied.
PPM was assessed by calculating the IEOA using the continuity equation. The threshold value for defining severe PPM (IEOA ≤ 0.9 cm 2 /m 2 ) was chosen on the basis of the classification used in previously published studies.
Early Postimplantation versus Follow-Up Hemodynamic Profiles
The Mayo Clinic written and electronic medical records for each of the 368 patients were searched to determine whether follow-up TTE was performed between 1 and 13 months after implantation of the SJM mechanical mitral valve prosthesis. Follow-up TTE was performed in 120 of the 368 patients (33%). One patient was excluded because follow-up TTE showed evidence of prosthetic thrombosis, and three patients were excluded because follow-up TTE demonstrated evidence of significant periprosthetic mitral regurgitation. These suspected prosthesis-related abnormalities were confirmed by TEE in all four patients and by surgical inspection in two of these four patients, one of whom underwent replacement of the SJM mechanical mitral valve prosthesis and one of whom underwent surgical repair of the periprosthetic leak. Of the other two patients, one underwent percutaneous closure of a perivalvular leak, and one patient with prosthetic thrombosis was treated with anticoagulation. Fourteen more patients were excluded because images for obtaining accurate and complete Doppler data were inadequate, and an additional four patients were excluded because they were tachycardic during TTE. The remaining 98 patients were included in the comparative analysis of early postimplantation versus follow-up echocardiographic hemodynamic profiles.
Statistical Analysis
The 23-mm valves were combined with the 25-mm valves for comparative analysis because there were only two 23-mm prostheses. Continuous variables were compared among the five valve-size groups using analysis of variance. Differences were considered significant at P < .05. Significant differences were investigated by adjusting for multiple comparisons using the Student-Newman-Keuls procedure.
Results
Baseline Clinical Characteristics
Table 1 summarizes the characteristics of the 368 patients who underwent implantation of SJM mechanical mitral valve prostheses. The indications for mitral valve replacement are listed in Table 2 . The median time between surgery and predischarge TTE was 5 days (range, 2-28 days). Heart rhythm was sinus in 222 patients (60%), atrial fibrillation in 99 (27%), atrial flutter in eight (2%), paced in 37 (10%), and junctional in two (1%). Fewer than half (155 [42%]) had trivial or mild mitral transprosthetic or periprosthetic regurgitation apparent during TTE.
| Variable | Prosthesis size | All patients | Range | ||||
|---|---|---|---|---|---|---|---|
| 25 mm ( n = 27) ∗ | 27 mm ( n = 67) | 29 mm ( n = 121) | 31 mm ( n = 115) | 33 mm ( n = 38) | |||
| Age (y) | 55 ± 16.3 | 56 ± 15.3 | 59 ± 11.7 | 57 ± 12.0 | 54 ± 14.5 | 57 ± 13.2 | 18-88 |
| Women | 25 (93%) | 58 (87%) | 80 (66%) | 54 (47%) | 16 (42%) | 233 (63%) | NA |
| Congenital heart disease | 1 (4%) | 1 (1%) | 5 (4%) | 6 (5%) | 3 (8%) | 16 (4%) | NA |
| Heart rate (beats/min) | 82 ± 7.8 | 79 ± 10.8 | 78 ± 11.3 | 79 ± 10.6 | 81 ± 10.7 | 79 ± 10.7 | 48-99 |
| Hemoglobin (g/dL) | 10.3 ± 1.13 | 10.4 ± 1.28 | 10.1 ± 1.55 | 10.3 ± 1.22 | 10.1 ± 1.18 | 10.2 ± 1.34 | 8.0-22.1 |
| Hematocrit (%) | 30.2 ± 3.31 | 30.1 ± 3.72 | 29.6 ± 3.24 | 30.3 ± 3.56 | 29.5 ± 3.33 | 30.0 ± 3.46 | 23.5-44.5 |
| BSA (m 2 ) | 1.66 ± 0.18 | 1.73 ± 0.20 | 1.85 ± 0.22 | 1.95 ± 0.22 | 1.91 ± 0.22 | 1.85 ± 0.24 | 1.35-2.66 |
| LVEF (%) | 59 ± 13.6 | 58 ± 11.4 | 56 ± 12.3 | 52 ± 13.6 | 47 ± 13.8 | 54 ± 13.2 | 15-76 |
| LVEF < 50% | 4 (15%) | 11 (16%) | 26 (22%) | 38 (33%) | 16 (42%) | 95 (26%) | NA |
| SV (mL) | 65 ± 18.2 | 69 ± 14.9 | 74 ± 16.7 | 77 ± 17.3 | 78 ± 18.3 | 74 ± 17.2 | 34-137 |
| SVI (mL/m 2 ) | 40 ± 10.3 | 40 ± 8.6 | 40 ± 7.7 | 39 ± 7.8 | 41 ± 8.6 | 40 ± 82 | 21-71 |
| PHT (msec) | 66 ± 14.3 | 63 ± 13.2 | 67 ± 16.4 | 68 ± 17.3 | 71 ± 17.5 | 67 ± 16.02 | 27-122 |
| MG (mm Hg) | 5.9 ± 1.57 | 4.7 ± 1.62 | 4.8 ± 1.68 | 4.4 ± 1.26 | 4.7 ± 1.47 | 4.7 ± 1.66 | 2-10 |
| E velocity (m/sec) | 1.9 ± 0.34 | 1.8 ± 0.32 | 1.8 ± 0.33 | 1.7 ± 0.34 | 1.7 ± 0.33 | 1.8 ± 0.34 | 0.6-2.7 |
| TVI MVP (cm) | 36 ± 7.8 | 33 ± 76.7 | 36 ± 7.6 | 34 ± 8.1 | 34 ± 6.9 | 35 ± 7.6 | 19-57 |
| TVI MVP /TVI LVOT | 1.7 ± 0.36 | 1.6 ± 0.42 | 1.7 ± 0.38 | 1.7 ± 0.44 | 1.8 ± 0.46 | 1.7 ± 0.41 | 0.8-4.0 |
| EOA (cm 2 ) † | 1.89 ± 0.56 | 2.11 ± 0.52 | 2.12 ± 0.46 | 2.32 ± 0.52 | 2.30 ± 0.58 | 2.18 ± 0.53 | 1.15-4.15 |
| IEOA (cm 2 /m 2 ) † | 1.14 ± 0.32 | 1.23 ± 0.31 | 1.16 ± 0.27 | 1.20 ± 0.31 | 1.21 ± 0.30 | 1.19 ± 0.30 | 0.60-2.29 |
| PPI † | 0.62 ± 0.18 | 0.57 ± 0.14 | 0.48 ± 0.11 | 0.45 ± 0.10 | 0.44 ± 0.11 | 0.49 ± 0.13 | 0.22-1.27 |
∗ The two 23-mm prostheses were included in the 25-mm group.
| Indication | n (%) |
|---|---|
| Rheumatic valve disease | 175 (48) |
| Mitral regurgitation | 101 (27) |
| Periprosthetic leak | 24 (7) |
| Radiation-induced valvulopathy | 11 (3) |
| Prosthetic valve regurgitation | 8 (2) |
| Prosthetic valve stenosis | 8 (2) |
| Native valve infective endocarditis | 7 (2) |
| Drug induced (ie, fenfluramine or dexfenfluramine plus phentermine or ergotamine) valvulopathy | 6 (2) |
| Prosthetic valve thrombosis | 6 (2) |
| Mitral valve stenosis (functional) after mitral valve repair | 3 (1) |
| Mitral valve stenosis, nonrheumatic | 3 (1) |
| Noninfective thrombotic endocarditis | 3 (1) |
| Prosthetic valve infective endocarditis | 3 (1) |
| Prosthetic valve mixed regurgitation and stenosis | 2 (1) |
| Mixed mitral stenosis and regurgitation (cleft mitral valve) | 2 (1) |
| PPM | 2 (1) |
| Maroteaux-Lamy syndrome | 1 (<1) |
| Carcinoid | 1 (<1) |
| Inflammatory valve disease (lupus related) | 1 (<1) |
| Congenital mitral valve | 1 (<1) |
Impact of Prosthesis Size
Valve size was 23 mm in two of the 368 patients (1%), 25 mm in 25 (7%), 27 mm in 67 (18%), 29 mm in 121 (33%), 31 mm in 115 (31%), and 33 mm in 38 (10%). The two 23-mm prostheses were included with the 25-mm prostheses ( n = 27) for analysis due to small sample size. Values for clinical and hemodynamic variables varied by valve size, but no significant differences were observed among valve sizes with respect to mean MG ( Figure 1 ), E velocity ( Figure 2 ), or TVI ratio ( Figure 3 ). EOA ( Figure 4 ) increased significantly with increasing valve size, but IEOA ( Figure 5 ) did not. PPI ( Figure 6 ) decreased significantly with increasing valve size. Body surface area (BSA) increased significantly with increasing valve size ( P < .001), whereas LVEF decreased significantly with increasing valve size ( P < .001). SV increased significantly with increasing prosthesis size ( P < .001), but SV index (SVI) did not increase significantly with increasing prosthesis size.
Subgroup analysis of the 31-mm and 33-mm valve sizes (both with GOAs of 5.18 cm 2 ) revealed that LVEF was significantly decreased in the 33-mm group compared with the 31-mm group ( P = .04), but there were no significant differences between patients with these two valve sizes for any of the remaining variables.
Effect of PPM
Fifty-five of the 368 patients (15%) in the current study had IEOAs ≤ 0.9 cm 2 /m 2 , which is indicative of severe mitral PPM. The hemodynamic profiles of these patients compared with those of the 313 patients with IEOAs > 0.9 cm 2 /m 2 are summarized in Table 3 . Patients with severe PPM had significantly lower LVEF, SV, SVI, EOA, and IEOA and higher MG, E velocity, TVI MVP , and TVI MVP /TVI LVOT than those of patients without severe PPM. PHT did not differ significantly between the two PPM groups.
| Variable | Prostheses with IEOAs ≤ 0.9 cm 2 /m 2 ( n = 55) | Prostheses with IEOAs > 0.9 cm 2 /m 2 ( n = 313) | P |
|---|---|---|---|
| BSA (m 2 ) | 2.01 (1.61-2.66) | 1.82 (1.35-2.40) | <.001 |
| LVEF (%) | 50 (20-71) | 55 (15-76) | .01 |
| SV (mL) | 67 (36-110) | 75 (34-137) | .002 |
| SVI (mL/m 2 ) | 33 (21-45) | 41 (23-71) | <.001 |
| EOA (cm 2 ) | 1.59 (1.15-2.20) | 2.28 (1.44-4.15) | <.001 |
| IEOA (cm 2 /m 2 ) | 0.79 (0.60-0.88) | 1.26 (0.91-2.29) | <.001 |
| MG (mm Hg) | 5.5 (2-9) | 4.6 (2-10) | <.001 |
| E velocity (m/sec) | 2.0 (1.2-2.7) | 1.7 (0.6-2.6) | <.001 |
| TVI MVP (cm) | 42 (27-57) | 33 (19-56) | <.001 |
| TVI MVP /TVI LVOT | 2.2 (1.4-4.0) | 1.6 (0.8-3.2) | <.001 |
| PHT (msec) | 71 (27-122) | 66 (31-118) | .18 |
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