Prosthesis-patient mismatch causes a significantly increased risk of operative mortality in aortic valve replacement

Physiological rules for the heart, lungs and other pressure-based organs

Background

The adherence of the heart to physical laws, such as Laplace's Law, may act as a measure of the organ's relative efficiency. Allometric relationships were investigated to assess the heart's efficiency concerning end-diastolic and end-systolic volumes, cardiac pressurization energy, cardiac output and mass.

Methods

Data to generate allometric relationships was obtained using a literature search, identifying heart and lung data across different mammalian and bird species. Statistical analysis was carried out using ordinary least squares (OLS) estimation.

Results

Near isometric relationships exist between body mass and seven parameters indicating no "efficiency of size" with scaling of the heart, and size-matching of the heart to the lungs and whole body. Even though there was equal efficiency in pressurization energy generation, cardiac output was maximally efficient in small mammals <10 kg and birds; the human heart reached only 71% efficiency. This loss in cardiac efficiency with increasing body mass can be explained by the aortic cross-section that scales following the three-quarter allometry law, compared to end-systolic and end-diastolic volumes that scale isometrically. The heart is therefore throttled by a relatively small aorta at large body size.

Conclusions

Mammalian and avian hearts operate at similar efficiencies, demonstrating a high degree of symmorphosis, however cardiac output efficiency decreases in larger animals due to a relatively negative aortic cross-section allometry. This work has a myriad of potential applications including explaining cardiac dysfunction in athletes, patient-prosthesis mismatch in aortic valve replacement and why heavy exercise is associated with a worse prognosis than mild or moderate exercise.

Moderate Patient-Prosthesis Mismatch Has No Negative Effect on Patients' Functional Status After Aortic Valve Replacement With CarboMedics Prosthesis

Background:

Patient-prosthesis mismatch (PPM) after aortic valve replacement (AVR) is the subject of continuing debate in the cardiac surgery field.

Objectives:

The aim of this study was to evaluate the frequency and severity of patient-prosthesis mismatch (PPM) and the functional status of patients undergoing aortic valve replacement (AVR) using a CarboMedics prosthesis in the mid-term follow up.

Patients and Methods:

We retrospectively studied 66 consecutive patients who were referred to AVR with a CarboMedics prosthesis at the Rajaie cardiovascular medical and research center, a university referral hospital in Tehran, Iran. The severity of PPM as well as clinical and echocardiographic parameters and the patients’ New York heat association (NYHA) functional classification status, operative data and postoperative complications, and mortality in a mid-term (4 - 5 months) follow up period was assessed. Severe PPM was defined as the effective orifice area (EOA) indexed to the patient’s body surface area (BSA) < 0.65 cm²/m² and moderate PPM was defined as the indexed effective orifice area (IEOA) between 0.65 and 0.85 cm²/m².

Results:

Of the 66 studied patients, 39 were male and 27 were female. The mean age of the patients was 43 ± 17 with a range of 6 - 76 years. Implanted sizes of the CarboMedics AV prosthesis in 22 patients were 19 and 21 mm, and in 44 patients were 23 and 25 mm. Eleven patients had moderate PPM (IEOA < 0.85 cm²/m²) and 55 of them did not have PPM (IEOA ≥ 0.85 cm²/m²). There were no statistically significant differences between the two groups in the echocardiographic trans-aortic pressure gradients (35.6 ± 19 vs. 23.2 ± 16 mmHg; P = 0.061) and the mean NYHA functional classification (1.10 ± 0.3 vs. 1.01 ± 0.10; P = 0.074) after AVR in the mid-term follow up.

Conclusions:

Moderate PPM has no negative effect on echocardiographic trans-aortic pressure gradients or the patients’ NYHA functional status after AVR with a CarboMedics prosthesis in the mid-term follow up.