Patient Selection

From the cardiac surgical database of Mayo Clinic, Rochester, Minnesota, we identified 2037 patients aged 18 years or more who underwent mitral valve replacement between 1995 and 2007. Of these 2037 patients, 755 (37%) had a bioprosthesis implanted. Of the 755 patients, 76 (10%) received HKII mitral valves, 122 (16%) received MM valves, and 80 (11%) received CEP valves. Of these 278 patients with an HKII, an MM, or a CEP valve, we excluded 26 patients who died within 30 days after surgery, 5 patients who did not undergo intraoperative transesophageal echocardiography (TEE), 52 patients who did not have a transthoracic echocardiogram (TTE) within 30 days after surgery, 6 patients who were on vasopressors at the time of their postoperative TTE, and 10 patients whose bioprostheses were deemed abnormal by intraoperative TEE or postoperative TTE. The remaining 179 patients constituted the study population: 36 patients with HKII bioprostheses, 86 patients with MM bioprostheses, and 57 patients with CEP bioprostheses.

The physical examination and appearance of the bioprostheses by both intraoperative TEE and TTE performed within 30 days after surgery showed them to be functioning normally in all 179 patients. No patient had greater than mild mitral valve prosthesis regurgitation or aortic valve regurgitation by intraoperative TEE or TTE.

The study was approved by the Mayo Clinic Institutional Review Board, and all participating patients provided written informed consent to allow the use of their medical records for research purposes. No industry support was provided for this study.

Echocardiographic Data

It is standard practice in our laboratory to average the Doppler measurements of 3 cycles if a patient is in sinus rhythm and to average ≥ 5 cycles if a patient is in 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 5 or more cycle lengths that are used for each parameter whenever possible. For all patients, the number of cycles is selected and the individual measurements are approved by the supervising echocardiographer before inclusion in the final report.

Doppler data were obtained by reviewing the postoperative TTE reports of patients. Missing measurements were obtained using off-line analysis (DigiView Image Management and Reporting System, Release 3.0; Digisonics, Houston, TX) by 2 of the investigators (L.A.B. and F.A.M.).

The bioprosthesis EOA was measured using both the PHT method used to calculate the EOA for native mitral valve stenosis (EOA = 220/PHT) and the continuity equation (EOA = stroke volume/TVI _MVP ) to compare these methods with each other and with in vitro EOA data for these specific prostheses. Other calculated variables included IEOA and TVI _MVP /TVI _LVOT . Cutoff values for MG, E velocity, TVI _MVP , TVI _MVP /TVI _LVOT , and PHT used to identify possible dysfunction in mitral valve bioprostheses in this series were determined by calculating the mean ± 2 standard deviations (SDs) for each variable.

The PPI was calculated as the ratio of the EOA derived from the continuity equation to the geometric orifice area (GOA) provided by the manufacturer. The GOAs for the HKII and MM mitral valves were 3.97 cm ² , 4.52 cm ² , 5.30 cm ² , and 6.15 cm ² for the 25-mm, 27-mm, 29-mm, and 31-mm valves, respectively, and 7.07 cm ² for the 33-mm MM valves. The GOAs for the CEP valves were 4.90 cm ² , 5.72 cm ² , and 6.60 cm ² for the 25-mm, 27-mm, and 29-mm valves, respectively, and 7.54 cm ² for the 31-mm and 33-mm valves.

Mitral valve prosthesis–patient mismatch (PPM) was assessed by calculating IEOA using the continuity equation. The threshold value chosen to define severe PPM (IEOA ≤ 0.9 cm ² /m ² ) was based on the results of previously published studies.

Statistical Analysis

Measurements were compared between the continuity equation and the PHT method by using a paired t test. Continuous variables were compared among the 5 valve size groups by using the analysis of variance procedure. Significant differences were investigated by adjusting for multiple comparisons using the Student Newman–Keuls procedure.

Clinical Characteristics

The characteristics of the 179 patients who had mitral valve bioprostheses implanted are listed in Tables 1 to 3 . The indications for mitral valve replacement were mitral regurgitation in 99 patients (55%), rheumatic valve disease in 50 patients (28%), native valve endocarditis in 10 patients (6%), prosthetic valve regurgitation in 10 patients (6%), prosthetic valve endocarditis in 5 patients (3%), prosthetic valve stenosis in 2 patients (1%), prosthetic valve thrombosis in 1 patient (<1%), mixed prosthetic valve regurgitation and stenosis in 1 patient (<1%), and accessory mitral valve tissue in 1 patient (<1%). Of the 179 patients, 128 (72%) had TTE performed within the first week after mitral valve replacement. The heart rhythm was sinus in 104 of the 179 patients (58%), atrial fibrillation in 49 patients (27%), atrial flutter in 5 patients (3%), and paced in 21 patients (12%).

Doppler Data

Hemodynamic data, grouped by valve size, are detailed in Tables 1 to 3 . Complete Doppler hemodynamic data were available for 149 (83%) of the 179 patients, including 17 patients with a heart rate ≥ 100 beats/min.

The calculated E velocity threshold values (mean ± 2 SD) for predicting probable normal bioprosthesis function were 2.5 m/s for the HKII bioprosthesis, 2.6 m/s for the MM bioprosthesis, and 2.2 m/s for the CEP bioprosthesis. Nearly all (170 [95%]) of the 179 patients in this study had an E velocity below these parameters. The threshold E velocity value for all 3 bioprosthesis types combined was 2.5 m/s. A total of 172 (96%) of the 179 patients had an E velocity ≤ 2.5 m/s.

The calculated cutoff values for TVI ratios predictive of normal bioprosthesis function were 3.6 for the HKII bioprosthesis, 3.5 for the MM bioprosthesis, and 2.7 for the CEP bioprosthesis. Most (175 [98%]) of the 179 patients had a TVI ratio less than or equal to these parameters. The threshold value for the TVI ratio for all 3 bioprostheses combined was 3.3. A total of 165 (97%) of the 170 patients in whom TVI _MVP /TVI _LVOT could be calculated had a TVI ratio ≤ 3.3.

The overall mean MG was 6.6 mm Hg for the 36 patients with an HKII, 6.4 mm Hg for the 86 patients with an MM, and 5.8 mm Hg for the 57 patients with a CEP bioprosthesis. There were 2 patients with an MG of 13 mm Hg. One patient had a large body surface area and was tachycardic (heart rate, 113 beats/min) during the TTE, and 1 patient was anemic, with hemoglobin and hematocrit values lower than those of the entire cohort (9.6 mg/dL and 28.5%, respectively). In addition, both patients had a left ventricular ejection fraction < 50% and an E velocity that was higher than the mean for the entire group of patients (2.4 m/s and 2.6 m/s, respectively). The threshold value for MG predictive of normal bioprosthesis function was 10.1 mm Hg, 9.7 mm Hg, and 8.6 mm Hg for the HKII, MM, and CEP mitral valve bioprostheses, respectively. Nearly all (169 [94%]) of the 179 patients in this study had an MG that was below these parameters. The threshold MG value for all 3 bioprostheses combined was 9.4. A total of 170 (95%) of the 179 patients had an MG ≤ 9.4 mm Hg.

The mean PHT was similar for all 3 types of valves (76-78 ms) and was < 124 ms in all patients in whom it could be measured. Threshold PHT values indicating probable normal bioprosthesis function were ≤ 115 ms for the HKII bioprosthesis, ≤ 108 ms for the MM bioprosthesis, ≤ 114 ms for the CEP bioprosthesis, and ≤ 111 ms for all 3 bioprostheses combined.

Effect of Bioprosthesis Size

Valve size was 25 mm in 10 (6%) of the 179 patients, 27 mm in 50 patients (28%), 29 mm in 63 patients (35%), 31 mm in 43 patients (24%), and 33 mm in 13 patients (7%). Body surface area was significantly larger with larger valve sizes for the HKII bioprosthesis ( P = .01) but not with the larger valve sizes for the MM or CEP bioprostheses. Mean left ventricular ejection fraction decreased with larger valve size for all 3 valve types, reaching statistical significance for the CEP bioprosthesis ( P = .03).

No significant differences were observed among the various valve sizes for all 3 bioprostheses with respect to mean MG, E velocity, TVI _MVP /TVI _LVOT , EOA, IEOA, or PPI ( Figures 1-3 ). There were also no significant differences found for any other hemodynamic parameters.

Plot of mean gradient, E velocity, TVI _MVP /TVI _LVOT , EOA CON, IEOA CON, and PPI CON for the Medtronic HKII (Medtronic, Inc, Minneapolis, MN) mitral valve bioprosthesis by valve size. Error bars indicate mean ± 2 SD. Sizes were jittered. EOA CON , Effective orifice area by the continuity equation; IEOA CON , indexed effective orifice area by the continuity equation; PPI CON , prosthesis performance index by the continuity equation; TVI _MVP / TVI _LVOT , ratio of the mitral valve prosthesis time-velocity integral to the left ventricular outflow tract time-velocity integral.

Plot of mean gradient, E velocity, TVI _MVP /TVI _LVOT , EOA CON, IEOA CON, and PPI CON for the MM (Medtronic, Inc) mitral valve bioprosthesis by valve size. Error bars indicate mean ± 2 SD. Sizes were jittered. EOA CON , Effective orifice area by the continuity equation; IEOA CON , indexed effective orifice area by the continuity equation; PPI CON , prosthesis performance index by the continuity equation; TVI _MVP / TVI _LVOT , ratio of the mitral valve prosthesis time-velocity integral to the left ventricular outflow tract time-velocity integral.

Plot of mean gradient, E velocity, TVI _MVP /TVI _LVOT , EOA CON, IEOA CON, and PPI CON for the CEP (Edwards Lifesciences LLC, Irvine, CA) pericardial mitral valve bioprosthesis by valve size. Error bars indicate mean ± 2 SD. Sizes were jittered. EOA CON , Effective orifice area by the continuity equation; IEOA CON , indexed effective orifice area by the continuity equation; PPI CON , prosthesis performance index by the continuity equation; TVI _MVP / TVI _LVOT , ratio of the mitral valve prosthesis time-velocity integral to the left ventricular outflow tract time-velocity integral.

Prosthesis Performance Index

PPI, the ratio of the EOA of the mitral valve prosthesis to the GOA, is a measure of how much of the primary GOA is used for flow. The PPI facilitates comparison of the efficiency of different valve designs. In the current study, the mean PPI was 0.33, 0.33, and 0.31 for the HKII, MM, and CEP bioprostheses, respectively. There was no correlation between PPI and valve size for any of the 3 types of mitral valves.

Effect of Prosthesis–Patient Mismatch

Among the 162 patients with a heart rate < 100 beats/min in whom IEOA could be calculated, 83 (51%) had an IEOA of ≤ 0.9 cm ² /m ² , which is consistent with severe mitral PPM. The hemodynamics for these patients versus those for patients with an IEOA > 0.9 cm ² /m ² are compared in Table 4 . For each prosthesis type, the mean MG, TVI _MVP , TVI _MVP /TVI _LVOT , and PHT by bioprosthesis size were larger for the patients with severe PPM than for the patients without severe PPM. Statistical comparison of these differences for each valve type was not possible because of the small number of bioprostheses in some valve size groups.

Table 4

Variables for the Medtronic Hancock II, Medtronic Mosaic, and Carpentier-Edwards Perimount mitral valve bioprostheses grouped according to indexed effective orifice area ^{∗ †}

Medtronic Hancock II with IEOA ≤ 0.9 cm 2 /m 2
Variable	25 mm (n = 2)	27 mm (n = 6)	29 mm (n = 10)	31 mm (n = 4)	33 mm (n = 0)	All patients (N = 22)
BSA, m 2	1.69 ± 0.06	1.79 ± 0.26	1.85 ± 0.15	2.11 ± 0.12	NA	1.86 ± 0.21
EOA CON, cm 2	1.11 ± 0.12	1.33 ± 0.25	1.31 ± 0.28	1.49 ± 0.27	NA	1.33 ± 0.26
IEOA CON, cm 2 /m 2	0.66 ± 0.10	0.74 ± 0.09	0.69 ± 0.13	0.70 ± 0.09	NA	0.71 ± 0.10
MG, mm Hg	7.5 ± 0.71	6.8 ± 1.60	6.1 ± 1.66	6.5 ± 2.38	NA	6.5 ± 1.68
E velocity, m/s	1.9 ± 0.07	1.9 ± 0.26	2.0 ± 0.24	2.1 ± 0.45	NA	2.0 ± 0.27
TVI MVP , cm	53 ± 5.7	53 ± 11.8	50 ± 13.1	52 ± 11.6	NA	52 ± 11.3
TVI MVP /TVI LVOT	2.3 ± 0.10	2.5 ± 0.48	2.8 ± 0.61	2.7 ± 0.31	NA	2.7 ± 0.49
PHT, ms	76 ± 13.4	95 ± 20.2	73 ± 17.5	87 ± 16.2	NA	82 ± 19.2

Medtronic Hancock II with IEOA > 0.9 cm 2 /m 2
Variable	25 mm (n = 1)	27 mm (n = 3)	29 mm (n = 7)	31 mm (n = 1)	33 mm (n = 0)	All patients (N = 12)
BSA, m 2	1.48	1.56 ± 0.06	1.69 ± 0.18	2.02	NA	1.67 ± 0.19
EOA CON, cm 2	2.11	1.70 ± 0.08	2.35 ± 0.65	1.96	NA	2.14 ± 0.56
IEOA CON, cm 2 /m 2	1.43	1.09 ± 0.07	1.39 ± 0.37	0.97	NA	1.29 ± 0.32
MG, mm Hg	2.0	6.7 ± 2.52	6.0 ± 2.00	8.0	NA	6.0 ± 2.30
E velocity, m/s	1.4	2.0 ± 0.26	1.8 ± 0.23	1.2	NA	1.8 ± 0.32
TVI MVP , cm	27	39 ± 9.2	39 ± 8.6	45	NA	39 ± 8.5
TVI MVP /TVI LVOT	1.4	1.7 ± 0.26	1.9 ± 0.49	2.5	NA	1.9 ± 0.46
PHT, ms	68	86 ± 8.0	66 ± 15.1	NA	NA	72 ± 15.5

Medtronic Mosaic with IEOA ≤ 0.9 cm 2 /m 2
Variable	25 mm (n = 2)	27 mm (n = 13)	29 mm (n = 15)	31 mm (n = 13)	33 mm (n = 0)	All patients (N = 43)
BSA, m 2	1.67 ± 0.08	1.82 ± 0.16	1.87 ± 0.18	1.98 ± 0.17	NA	1.88 ± 0.18
EOA CON, cm 2	1.26 ± 0.08	1.31 ± 0.19	1.27 ± 0.23	1.56 ± 0.21	NA	1.37 ± 0.24
IEOA CON, cm 2 /m 2	0.75 ± 0.08	0.71 ± 0.11	0.68 ± 0.12	0.79 ± 0.09	NA	0.73 ± 0.11
MG, mm Hg	7.5 ± 2.12	5.9 ± 1.12	6.7 ± 2.19	6.6 ± 1.45	NA	6.5 ± 1.68
E velocity, m/s	2.2 ± 0.14	2.1 ± 0.30	2.1 ± 0.34	2.1 ± 0.28	NA	2.1 ± 0.30
TVI MVP , cm	50 ± 0.7	54 ± 10.8	54 ± 12.4	49 ± 5.8	NA	52 ± 10.0
TVI MVP /TVI LVOT	2.4 (n = 1)	2.6 ± 0.46	2.9 ± 0.58	2.6 ± 0.57	NA	2.7 ± 0.53
PHT, ms	90 (n = 1)	81 ± 19.1	80 ± 13.9	76 ± 14.4	NA	79 ± 15.3

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