M. Loebe

Pathophysiologic role of contact activation in bleeding followed by thromboembolic complications after implantation of a ventricular assist device

The time period after implantation of a ventricular assist device in patients with end-stage heart disease is complicated by hemorrhage in the early postoperative period and by thromboembolism in the later course. To investigate the pathophysiologic role of contact activation in 12 bridging patients (10 patients with a paracorporeal Berlin Heart [Berlin Heart GmbH, Berlin, Germany], 2 patients with an intracorporeal Novacor system [Novacor N100; Baxter, Oakland, CA]), hemostatic parameters were determined until heart transplantation or at least up to the 51st postoperative day. The following were observed: 1) In the early postoperative period, until day 15, levels of contact factors XI, XII, and prekallikrein were below normal, whereas levels of plasmin-a2-antiplasmin (PAP) complexes were elevated. Thrombin-antithrombin III (TAT) complexes, as well as platelet factor 4 and beta-thromboglobulin, significantly increased immediately after surgery. 2) In the later postoperative period, starting with the third postoperative week, an increase of factors XI, XII, and prekallikrein was observed. PAP and TAT complexes, as well as platelet factor 4 and beta-thromboglobulin, remained elevated. It is concluded that, in the early postoperative period, hemostasis is influenced mainly by an activation of the intrinsic contact system dependent fibrinolytic system with consumption of contact factors and increased levels of PAP complexes, whereas later system dependent fibrinolysis becomes less important, leading to a shift of the balance toward coagulation, with sustained prothrombin and platelet activation. This is in accord with the observed clinical complications (e.g., early postoperative bleeding, and thromboembolic events later on).

Mechanical Circulatory Support as a Bridge to Transplantation: Berlin Experience in 154 Patients

Circulatory support with an artificial heart provides a valuable supplement in the field of heart transplantation. An artificial heart can be implanted before a suitable donor organ is available, or after heart transplantation if unmanageable acute graft rejection or insufficiency develops. The so-called bridge procedure, i.e., artificial heart support followed by heart transplantation, was introduced by Cooley in 1969 with the use of the Liotta total artificial heart (TAH) [1]. Thirteen years later, the Jarvik-7 (Symbion, Salt Lake City, UT, USA) TAH was permanently implanted in a human for the first time by DeVries et al. [2]. Although initially all of the TAH recipients died of multiple complications, close examination of the results provided many cautionary lessons for the clinical use of artificial hearts. The first successful bridging was performed in 1984 by Starnes et al. [3], who used an implantable Novacor (Baxter Healthcare, Novacor Division, Oakland, CA, USA) left ventricular assist device (LVAD), followed by Hill et al. [4] with a Pierce-Donachy LVAD, and in 1985 by Copeland et al. [5] with a Jarvik-7 TAH. During the ensuing decade, the bridge-to-transplantation procedure spread all over the world with increasing success.

Radiologic anatomy of ventricular assist devices

Ventricular assist devices (VAD) allow for long-term circulatory support of patients with end-stage heart failure. With the increasing duration of circulatory support, diagnostic imaging plays an important role in the management of patients on a VAD. The aim of our review was to analyze the radiologic features of different VADs. From 1987 to 1996, 319 patients (mean age 42 years, range 3 to 74 years) were treated with a VAD. A Berlin Heart VAD was implanted in 263 of the patients, the univentricular Baxtor Novacor was implanted in three patients, and the univentricular CI Heartmate was implanted in 19 patients. All patients were studied by serial chest radiographs. In addition, 70 patients underwent computed tomography (CT), and five patients underwent electron beam CT. The Berlin Heart VAD was used as a biventricular support system in 218 patients. In all cases, the position of the wire-directed cannulae was identified on the chest radiographs, while the exact position of the cannula tip could be visualized by CT only. The plastic cannulae of both the Novacor and the Heartmate were not discernible on radiographs, but required CT for evaluation. Computed tomography also resolved the metal components of the pumps. The titanium-made pump housing of the Heartmate caused beam-hardening artefacts that might conceal fluid accumulations in the pump pocket. Computed tomography is the standard of reference for examinations of cannula position, pump position, and pump components of ventricular assist devices.

CLINICAL SIGNIFICANCE OF PIA POLYMORPHISM OF PLATELET GP IIb/IIIa RECEPTORS DURING LONG-TERM VAD SUPPORT

BACKGROUNDnAlthough bleeding and thromboembolism remain major complications after implantation of ventricular assist devices (VADs), no standard anticoagulation protocols are available. Genetic polymorphism of platelet glycoprotein IIb/IIIa may contribute to the development of complications. The present study demonstrates a relationship between the PlA genotype and postoperative complications in patients implanted with pulsatile and axial flow VADs.nnnMETHODSnThe PlA genotype was determined in 41 consecutive patients treated with a VAD who received anticoagulation with phenprocoumon and aspirin. Pulsatile Novacor (Novacor Corp, Oakland, CA) and Berlin Heart VADs (Berlin Heart, Berlin, Germany) were implanted in 28 patients and the axial flow MicroMed DeBakey VAD (MicroMed Technology, Inc, Houston, TX) in 13. The relationship between the PlA genotype, the anticoagulation regime, and bleeding and thromboembolic events was analyzed.nnnRESULTSnThere were no differences between patients with the A1A1 and A1A2 genotype regarding demographic characteristics, weight, or infection episodes. The international normalized ratio (INR), platelet activation tests, and doses of aspirin and dipyridamol before events were similar in both groups. Patients with the A1A1 genotype developed more bleeding complications (39% vs 0%, p = 0.021), while patients with the A1A2 genotype showed a tendency toward more thromboembolic events (13% vs 30%, p = 0.33). With regard to different types of VAD, patients with the axial flow DeBakey VAD and the A1A1 genotype developed significantly more bleeding complications (70% vs 0%, p = 0.033).nnnCONCLUSIONSnIn patients with a long-term VAD determination of PlA polymorphism and subsequent adjustment of the anticoagulation regime may lead to a reduction of bleeding and thromboembolic complications.

Magnetresonanztomographie bei Trägern künstlicher Herzklappen

Zusammenfassung Die Indikationen zur Magnetresonanztomographie (MRT) bei Trägern künstlicher Herzklappen sind kritisch. Eine generelle Kontraindikation gegen die MRT ist zweifelhaft. Einige diagnostische Fragestellungen wie Prozesse in der hinteren Schädelgrube, Spinalabszesse und bei Beschwerden im Inneren des Knies lassen sich durch die MRT besser untersuchen als mit anderen radiologischen Verfahren. Die MRT kann Träger künstlicher Herzklappen auf dreierlei Weise direkt beeinträchtigen: 1) Bewegung und Dislozierung der Klappenprothese, 2) Erwärmung und 3) Induktion von Arrhythmien durch elektrische Ströme, und indirekt durch eine Verzerrung des MRT-Bildes mit der Gefahr einer diagnostischen Fehlinterpretation. Die gegenwärtige Literatur über Sicherheitsaspekte der MRT bei Trägern künstlicher Herzklappen erscheint nicht ausreichend. u2002u2009u2009Deshalb wurde 1998 eine Umfrage unter fünfundzwanzig Herstellern künstlicher Herzklappen durchgeführt bezüglich der Kompatibilität, Sicherheit, oder der Kontraindikation der MRT ihrer jeweiligen Klappenprothese. Die in Europa führenden Klappen-Hersteller bescheinigten eine MRT-Sicherheit. Einige Firmen stützten ihre Aussagen auf nicht einzusehende Untersuchungen, oder übertrugen die Verantwortung auf den Arzt, der die MRT durchführt. Andere Firmen gaben keine MRT-Sicherheitsgarantie oder antworteten nicht. Zwei Klappenhersteller warnten explizit vor der MRT bei bestimmten Prothesentypen. Aufbauend auf unsere Umfrage wird ein Überblick über die technischen Aspekte, die klinischen Umstände und die Voraussetzungen für MRT-Sicherheitsstandards bei Trägern künstlicher Herzklappen gegeben.Summary The indications for magnetic resonance imaging (MRI) on prosthetic heart valve recipients remain critical. A generalized contraindication for MRI is doubtful. Some diagnostic questions such as interests in pathologies of the posterior cranial fossa, spinal abscesses, and internal derangements for the knee, strongly recommend the advantages of MRI versus all other radiological diagnostic techniques. MRI can directly affect patients with prosthetic valves in three ways by: 1) movement or dislodgment of the prosthesis, 2) heating, and 3) arrhythmias induced by electric currents, and indirectly by distortion of the image and its subsequent misinterpretation. Present literature that concerns the safety considerations of current values appears to be incomplete. u2002u2009u2009Therefore, a survey of twenty-five valve manufacturers with regard to compatibility, safety or contraindication for MRI on their respective prosthetic heart valves was performed in 1998. Those manufacturers who distribute most of the valves in Europe confirmed the safety of MRI. However, some gave their assurances based on inadequate data, or assigned all responsibility to the physician. Some companies did not give any assurance for MRI safety or failed to respond to our enquiry. Two valve manufacturers warned against performing MRI on certain prostheses. Based on our 1998 questionnaire, the technical issues, the clinical circumstances, the prerequisites and criteria for and the definition of safety standards for MRI on prosthetic heart valve recipients are presented in this paper.