Mechanical heart valve cavitation in patients with bileaflet valves.

Today, the quality of mechanical heart valves is quite high, and implantation has become a routine clinical procedure with a low operative mortality (< 5%). However, patients still face the risks of blood cell damage, thromboembolic events, and material failure of the prosthetic device. One mechanism found to be a possible contributor to these adverse effects is cavitation. In vitro, cavitation has been directly demonstrated by visualization and indirectly in vivo by registering of high frequency pressure fluctuations (HFPF). Tilting disc valves are thought of having higher cavitation potential than bileaflet valves due to higher closing velocities. However, the thromboembolic potential seems to be the same. Further studies are therefore needed to investigate the cavitation potential of bileaflet valves in vivo. The post processing of HFPF have shown difficulties when applied on bileaflet vavles due to asynchronous closure of the two leaflets. The aim of this study was therefore to isolate the pressure signature from each leaflet closure and perform cavitation analyses on each component. Six patients were included in the study (St. Jude Medical (n=3) and CarboMedics (n=3); all aortic bileaflet mechanical heart valves). HFPFs were recorded intraoperatively through a hydrophone at the aortic root. The pressure signature relating to the first and second leaflet closure was isolated and cavitation parameters were calculated (RMS after 50 kHz highpass filtering and signal energy). Data were averaged over 30 heart cycles. For all patients both the RMS value and signal energy of the second leaflet closure were higher than for the first leaflet closure. This indicates that the second leaflet closure is most prone to cause cavitation. Therefore, quantifying cavitation based on the HFPF related to the second leaflet closure may suggest that the cavitation potential for bileaflet valves in vivo may be higher than previous studies have suggested.

Effect of fish oil (n-3 polyunsaturated fatty acids) on plasma lipids, lipoproteins and inflammatory markers in HIV-infected patients treated with antiretroviral therapy: a randomized, double-blind, placebo-controlled study.

Patients on antiretroviral therapy are reported to have an increased risk of cardiovascular disease. We aimed to investigate the effect of n-3 polyunsaturated fatty acids (n-3 PUFAs) on plasma lipids, lipoproteins and inflammatory markers in HIV-infected patients treated with antiretroviral therapy. We randomized 51 patients in a placebo-controlled, double-blind trial to receive either 2 capsules of Omacor twice daily or 2 capsules of placebo. Compliance was measured by determining levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in neutrophils. Plasma triglycerides were reduced in the n-3 PUFA group by 0.14 mmol/l after 12 weeks of treatment (n=26), while plasma triglycerides increased by 0.36 mmol/l in the control group (n=25). The difference between groups was significant, p=0.03. No significant effect of treatment was found for total cholesterol, high-density lipoprotein (HDL) or low-density lipoprotein (LDL) cholesterol or apolipoproteins. There was a significant increase in leukotriene B5 (LTB5) and LTB5/LTB4 ratio in the n-3 PUFA group compared to the control group. Baseline values for intercellular adhesion molecule-1 (ICAM), vascular cell adhesion molecule-1 (VCAM) and highly sensitive C-reactive protein (hsCRP) were comparable at baseline, and the intervention did not change these parameters significantly. The present study showed that treatment with n-3 PUFA slightly decreased plasma triglycerides and induced anti-inflammatory effects by increasing formation of anti-inflammatory LTB5.

Quantitative evaluation of a novel sensor for measuring muscular tissue flow and gases.

Information about muscular tissue flow is important for diagnosing, treating and monitoring patients with tissue ischemia. For this purpose an objective method which is reproducible and continuous is needed. In co-operation with the company Unisense A/S, we have developed a sensor for instantaneous and continuous monitoring of muscle tissue flow in vivo. The method is based on a flexible microsensor which emits and measures minute amounts of inert tracer gases. The objective was to evaluate the capability of the microsensor to measure varying degrees of tissue flow changes and compare these measurements with the 133Xenon Washout Technique for measuring local perfusion rates in skeletal muscle. The Unisense microsensor was tested in the gracilis muscle of six anaesthetized pigs subjected to varying degrees of muscle ischemia. We found that both tissue flow and pO2 declined in synchrony with reduced blood flow to the lower extremities. All the data from the Unisense microsensor show the same trend as the Xenon data and thus confirms that the microsensor can measure changes in tissue flow.

Intraoperative and postoperative evaluation of cavitation in mechanical heart valve patients.

BACKGROUND: Cavitation has been claimed partly responsible for the increased risk of thromboembolic complications, hemolysis, and fatal valve failure seen in mechanical heart valve patients. In vivo studies have investigated cavitation using high-pass filtering of the high-frequency pressure fluctuations with the root mean square values as an assessment of intensities. In vitro studies have shown that this well-known method may not be ideal owing to loss of data as a consequence of filtering, and because it requires a priori knowledge of the valve resonance pattern. Therefore, a new method has been developed, which decomposes the signal into nondeterministic (cavitation) and deterministic (valve resonance) signal components, and hence decreases data loss. This study aimed to evaluate cavitation in patients with mechanical, biological, and native heart valves both intraoperatively and postoperatively using the new method. METHODS: High-frequency pressure fluctuations were measured by a hydrophone intraoperatively and postoperatively in 14 patients with mechanical valves, 10 patients with normal aortic valves, and 5 patients with bioprosthesis. The total signal energy was evaluated as nondeterministic and deterministic energies. RESULTS: Nondeterministic energies were verified both intraoperatively and postoperatively in all patients who had a mechanical valve; this finding confirms the cavitation potential of mechanical valves. None of the data recorded in patients with bioprosthetic or native valves contained nondeterministic energy. CONCLUSIONS: The study confirms the presence of cavitation in mechanical heart valve patients using the nondeterministic energy of high-frequency pressure fluctuations as a quantitative measure of cavitation both intraoperatively and postoperatively.

In-vivo prediction of cavitation near a Medtronic Hall valve.

BACKGROUND AND AIM OF THE STUDY: Quantification of cavitation near mechanical heart valves in vivo is currently based on measurements of high-frequency pressure fluctuations (HFPF). Until now, mechanical resonance components have been removed using a high-pass filter. However, isolating cavitation and resonance signal components by separating the deterministic and non-deterministic parts of the HFPF signal has recently been proposed as a new method. It was hypothesized that the non-deterministic signal energy, Enon-det, of the HFPF signal correlates with previous parameters indicating cavitation in vivo, specifically the root mean square pressure after appropriate high-pass filtering (P(RMS)) and the rate of change in transvalvular pressure with respect to time (dP/dt). METHODS: Medtronic Hall 29 mm mitral valves were implanted in five pigs (body weight 80 kg). The hemodynamic condition was varied by infusion of dobutamine and blood volume regulation to achieve a wide range of dP/dt (100 to 4,700 mmHg/s). According to previous studies, P(RMS) was deduced using the HP-filtering cut-off frequency of 50 kHz for this particular valve. The transvalvular dP/dt was derived as the average slope 5 ms prior to valve closure. RESULTS: Power relationships were found between Enon-det and P(RMS) (P(RMS) = 1.27 x Enon-det0.49), and between Enon-det and dP/dt. The correlation between Enon-det and P(RMS) was very strong (r = 0.98), whereas the correlation between Enon-det and dP/dt was notably weaker (r = 0.68). CONCLUSION: Enon-det was an excellent predictor of P(RMS), obtained after appropriate filtering. The present data suggested that the signal energy above 50 kHz was almost completely non-deterministic. It can therefore be proposed that Enon-det is a more direct and easily accessible parameter than those previously suggested for the purpose of cavitation quantification. This parameter is able to quantify the pressure fluctuations thought to occur from cavitation in vivo, and may be applicable for non-invasive recordings.

Indication of cavitation in mechanical heart valve patients.

BACKGROUND AND AIM OF THE STUDY: Cavitation may cause erosion of prosthetic heart valve material. The phenomenon has been extensively studied in vitro, and an association between the presence of cavitation bubbles and high-frequency pressure fluctuations (HFPF) has been established. In-vivo studies examining this phenomenon are scarce; hence, the study aim was to compare HFPF in patients with native, bioprosthetic or mechanical aortic valves, using both invasive and non-invasive measuring techniques. METHODS: Measurements were carried out in 16 patients implanted with a St. Jude Medical aortic valve; two control groups comprised 10 patients with normal aortic valves after coronary artery bypass surgery, and five patients implanted with a Carpentier-Edwards pericardial aortic bioprosthesis. HFPF were measured intraoperatively using a hydrophone placed near the aortic annulus, and postoperatively using the same hydrophone mounted in a specially designed water-filled sound chamber. The frequency spectrum was evaluated using Fast Fourier transformation, and the root mean square (RMS) value of the pressure signals was calculated in the frequency range 50-150 kHz. RESULTS: HFPF with intensities significantly above the noise floor were registered using both methods in the vicinity of mechanical heart valves. The RMS values of the HFPF for all three patient groups measured intra- and postoperatively disclosed a significant difference between the mechanical valves and the two control groups, indicating that there is no cavitation in the vicinity of the biological or the native valves. CONCLUSION: HFPF are present in the vicinity of mechanical aortic valves and can be measured in patients, both invasively and non-invasively. This indication of cavitation was not observed in patients with either native or bioprosthetic aortic valves.