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.

Revascularization compared to medical treatment in patients with silent vs. symptomatic residual ischemia after thrombolyzed myocardial infarction--the DANAMI study.

AIMS: The aim was to compare the effect of revascularization to conservative treatment in patients with residual silent and with residual symptomatic ischemia following acute myocardial infarction (AMI). The study was a subanalysis of the DANAMI (DANish AMI) randomized study of invasive vs. conservative treatment in patients with inducible ischemia after thrombolysis in AMI. METHODS AND RESULTS: One thousand and eight patients were randomized to invasive or conservative treatment, stratified by the type of ischemia: silent, i.e. ST depression during an exercise test prior to discharge in 56%, or symptomatic, i.e. chest pain occurring either spontaneously during admission or during the exercise test, with or without ST changes, in 44%. Compared to a conservative strategy, invasive treatment reduced the incidence of nonfatal reinfarction, after in median 2.4 years, in both symptomatic patients (13.3-7.2%, p < 0.006) and patients with silent ischemia (10.1 vs. 5.7%, p < 0.05), and of admissions with unstable angina in symptomatic (44.5-27.6%, p < 0.0001) and silent ischemia (21.6-13.3%, p < 0.0006). CONCLUSIONS: Compared to conservative strategy, invasive treatment reduces the risk of nonfatal reinfarction and hospital admissions for unstable angina in thrombolyzed post-AMI patients with silent as well as symptomatic exercise-induced ischemia.

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.

Imbalanced chordal force distribution causes acute ischemic mitral regurgitation: mechanistic insights from chordae tendineae force measurements in pigs.

BACKGROUND: Ischemic mitral regurgitation is caused by an imbalance of the entire mitral-ventricular complex. This interaction is mediated through the chordae tendineae force distribution, which may perturb several elements of the mitral valve apparatus. Our objective was to investigate the association between the mitral valvular 3-dimensional geometric perturbations and chordae tendineae force redistribution in a porcine model of acute ischemic mitral regurgitation. METHODS: In 9 pigs, acute ischemic mitral regurgitation was induced by repeated microembolization of the left circumflex coronary artery. Mitral leaflet coaptation geometry was determined by 2-dimensional echocardiography and reconstructed 3-dimensionally. Leading edge chordal forces were measured by dedicated miniature force transducers at control and during ischemic mitral regurgitation. RESULTS: During acute ischemic mitral regurgitation, there was a decreased tension of the primary chorda from the ischemic posterior left ventricular wall to the anterior leaflet (0.295 +/- 0.063 N vs 0.336 +/- 0.071 N [control]; P < .05). The tension of the chorda from the nonischemic anterior left ventricular wall to the anterior leaflet increased (0.375 +/- 0.066 N vs 0.333 +/- 0.071 N [control]; P < .05). In accordance, relative leaflet prolapse was observed at the ischemic commissural side, whereas there was an increase in the leaflet surface area at the nonischemic commissural side, indicating localized leaflet tethering. CONCLUSIONS: Acute ischemic mitral regurgitation due to posterior left ventricular wall ischemia was associated with focal chordal and leaflet tethering at the nonischemic commissural portion of the mitral valve and a paradoxical decrease of the chordal forces and relative prolapse at the ischemic site of the anterior mitral valve leaflet.

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.

Cavitation caused by mechanical heart valve prostheses--a review.

Heart valve dysfunction often necessitates surgical implantation of a mechanical heart valve (MHV). Although implantation of a MHV is a life-saving procedure, the patient still faces potentially complications such as thromboembolic events and material failure. These complications may be caused by cavitation, which can occur during valve closure. Cavitation is an erosive phenomenon that can be generated in fluids when the pressure locally drops below the vapor pressure. This paper reviews the literature on cavitation and MHVs and particular features of the valve and closing conditions that potentially increase the intensity of cavitation. Techniques for detecting cavitation will be discussed. Of these, an acoustic approach will be emphasized, since it is currently the only technique able to detect and quantify cavitation in vivo.

Intraventricular dispersion and temporal delay of early left ventricular filling after acute myocardial infarction. Assessment by magnetic resonance velocity mapping.

This article aims to describe early left ventricular diastolic inflow using magnetic resonance velocity mapping in patients with recent acute myocardial infarction and in normal volunteers. Magnetic resonance velocity mapping was performed in a long axis plane through the hearts of 46 patients with recent, first time acute myocardial infarction and 43 age-matched normal volunteers. The peak velocities at six levels of the early diastolic inflow stream were recorded. A velocity index was calculated as the peak velocity in each position relative to the peak velocity at the mitral leaflet tips. Also, the temporal delay of velocity propagation was computed. Velocity index 4 cm downstream of mitral leaflet tips was lower in the acute myocardial infarction group (0.42 (0.17)) (mean (SD)) compared to controls (0.59 (0.25)) (p < 0.001). Temporal delay in the same position was longer in the acute myocardial infarction group (62 (67) ms) than in controls (32 (39) ms) (p < 0.02). Blood flow patterns in patients after acute myocardial infarction were characterized by increased dispersion of velocities and increased temporal delay of velocity propagation, probably reflecting impaired active left ventricular relaxation. Intraventricular flow measurements constitute a promising new technique for non-invasive assessment of left ventricular diastolic function.