Extended in vivo evaluation of a miniaturized axial flow pump with a novel inflow cannula for a minimal invasive implantation procedure.

BACKGROUND: Minimally invasive techniques are desirable to minimize surgical trauma during left ventricular assist device (LVAD) implantation. This is particularly challenging for full-flow support. In this study, a minimally invasive implantation technique was developed for a microaxial rotary pump. The system was evaluated in a chronic sheep model. METHODS: A HeartWare MVAD (HeartWare, Miami Lakes, FL) pump (length, 50 mm; diameter, 21 mm; maximum flow, 7-8 liters/min) was combined with a novel inflow cannula, including a new flow-optimized tip. The device was implanted into sheep (range, 60-80 kg, mean, 71.6 ± 6.8 kg) through a right-sided minithoracotomy. The inflow cannula was inserted through the superior pulmonary vein, passing through the left atrium into the left ventricle. Scheduled implant period was 30 days for 8 sheep and 100 days for 3 sheep. Mean support flow was set to half of the nominal cardiac output. RESULTS: Six of 8 sheep finished the scheduled 30-day investigation period (one failed due to early non-pump-related post-operative bleeding and one due to prototype controller failure). The 3 sheep scheduled for 100 days reached the study end point. Peak pump flows of up to 6.9 liters/min were achieved. At necropsy, no signs of mitral valve lesions or thrombus formation around the cannula, the tip, or the insertion site were observed, except for valve leaflet erosion in 1 animal, where the cannula had been entangled in the sub-valvular chords due to lack of ultrasound monitoring. CONCLUSIONS: The minimally invasive implantation technique using the HeartWare MVAD pump, together with a new cannula, provided excellent results in a chronic animal model.

Emergency cardio-pulmonary bypass in cardiac arrest: seventeen years of experience.

AIM: Emergency cardiopulmonary bypass (E-CPB) is an advanced and rarely used procedure for patients in cardiac arrest that do not regain restoration of spontaneous circulation with standard resuscitation methods. The feasibility, safety and outcome of the intervention with E-CPB in cardiac arrest situations at our department have been evaluated. METHODS: Clinical presentation, time intervals, diagnosis and outcome of all patients who received E-CPB at an emergency department of a tertiary care university hospital were evaluated. Patient charts were reviewed regarding cardiac arrest variables and treatment data of all patients from 1993 to 2010. RESULTS: E-CPB was performed in 55 patients. Of all patients, 33 (60%) were male and the median age was 32 years (IQR 24-44). In all cases cardiac arrest was witnessed. The first recorded ECG rhythm showed pulseless electric activity in 23 (42%), ventricular fibrillation in 21 (38%) and asystole in 11 (20%) patients. Cardiac arrest occurred out-of-hospital in 33 (60%) patients. The median duration of CPR before performing E-CPB was 86 min (IQR 69-121). The median 'cannulation'-time was 33 min (IQR 21-45) and the duration on bypass was 311 min (IQR 161-953). Cardiac causes of arrest were found in 19 (35%) patients. Eight patients (15%) survived to 6 months with good neurological outcome. CONCLUSION: E-CPB for cardiac arrest is feasible and safe. In this seemingly desperate patient population after prolonged cardiac arrest, we observed a high survival rate of 15%. E-CPB is a meaningful treatment option, which should be considered more often and earlier.

Intuitive use and usability of ventricular assist device peripheral components in simulated emergency conditions.

Ventricular assist devices (VADs) are now increasingly used to prolong the lives of end-stage heart failure patients. These patients vary greatly in age, alertness, activity, and home environment. In daily routine, but especially in emergencies or in conjunction with non-VAD-correlated diseases, the untrained, intuitive use and application of VAD peripherals by relatives, laypersons, and paramedics becomes important. Correct intuitive use may be a matter of life and death. The aim of this study was to evaluate the intuitive usability of these systems and to identify key features needed to optimize intuitive use. Paramedics (n=96) were confronted with a simulated emergency situation involving VAD peripherals mounted on a dummy. Three conditions were simulated: the VAD disconnected from its power source (n=44); both VAD batteries empty (n=44); and a discharged VAD battery mistakenly connected in place of a charged one (n=8). Two VAD systems were assessed: the Heartware HVAD and the Thoratec HeartMate II. An appropriate emergency card developed by our center was available in each case. Actions were videotaped, response times were measured, and a standardized questionnaire was completed after the simulation. The problem was solved by 71% of the participants (HVAD 83%, HMII 60%) with 87% using the emergency card. Only 4% could solve the problem without. Cardiac massage, which was unnecessary, was started by 44%, while 18% complained about unnecessarily difficult conditions (e.g., irritation from the acoustic alarm, complexity of the emergency card, error-prone procedures). Better component labeling (e.g., displays, control elements, connectors) was recommended by 56%. A thoroughly color-coded connection system was especially desired. Cable- and connector-related difficulties were reported by 23%. The study indicated that VAD systems should be self-explaining, with clear labeling of components and connectors, that a clearer emergency card is pivotal and that similar basic handling and emergency procedures for all VAD types would be desirable.

Usability and safety of ventricular assist devices: human factors and design aspects.

The purpose of this study was the investigation of the usability and ergonomics of ventricular assist devices (VADs) in everyday usage. Patients with four different VAD types were observed. After implantation, instruction, and discharge from the hospital, the patients returned on a regular basis to the outpatient clinic, where the investigation took place. Data collection took place in two phases. In phase I home-released VAD patients were asked about perceived problems with the system at home. Additionally health-care professionals were interviewed to gather information on frequent VAD inconveniences and shortcomings. This inquiry resulted in a standardized self-assessment questionnaire and a manual skill test, which were performed in phase II by the whole collective (16 patients and ongoing). As a result, 38% of the patients disconnected parts of their system unintentionally at least once. All of them ascribed this problem to their own carelessness. Thirty-eight percent had to replace a cable. Seventy-five percent desired an additional cable strain relief. Thirty-eight percent suffered from rubbing of parts on the body. Sixty-three percent used a separate repository aside from the factory-provided transportation systems. The overall noise emission (pump, ventilators, and alarms) annoyed 56%; however, for 32% the alarm signals were too quiet to wake them up. No correlation between the assessed manual skills and the number of adverse events was found. To conclude, this preliminary study revealed considerable potential for improvements in the usability of ventricular assist systems.

Extracorporeal venovenous cooling for induction of mild hypothermia in human-sized swine.

OBJECTIVE: Several cooling methods have been investigated for inducing mild hypothermia (33-36 degrees C) after cardiac arrest, brain trauma, or stroke. To achieve its best effect, therapeutic hypothermia has to be applied very early after the ischemic insult; otherwise, the beneficial effect would be diminished or even abrogated. The aim of this study was to investigate the effectiveness and safety of extracorporeal venovenous cooling as compared with endovascular cooling. DESIGN: Swine were cooled in a randomized crossover design from 38 degrees C to 33 degrees C brain temperature, either with extracorporeal venovenous cooling or with endovascular cooling. SETTING: Laboratory investigation. SUBJECTS: Six swine of human size (85 to 101 kg). INTERVENTIONS: Swine were randomly cooled with the first device, and after achieving the target brain temperature, re-warmed via the same technique and with heating lamps to baseline temperature. Then the other catheter was inserted and cooling was performed with the second device. MEASUREMENTS: Brain, pulmonary artery and tympanic temperature, blood pressure, and heart rate were recorded continuously. Laboratory samples, including free hemoglobin, were taken at predefined temperature points during cooling. Comparisons between and within (baseline vs. 33 degrees C) the treatment groups were performed with the paired Student's t-test. MAIN RESULTS: The time needed to reduce brain temperature from 38.0 degrees C to 33.0 degrees C was 41 +/- 17 mins with venovenous cooling and 126 +/- 37 mins with endovascular cooling (p = .001). Heart rate and mean arterial pressure decreased moderately during cooling and were significantly lower at 33 degrees C than at baseline in both groups, without differences between groups. None of the swine developed significant hemolysis, arrhythmias, or bleeding. CONCLUSIONS: Extracorporeal venovenous cooling was an effective and safe method to rapidly induce therapeutic mild hypothermia in human-sized swine. It seems to be promising for further application and investigation in patients.

Transmyocardial laser revascularization: epicardial ECG detection provides efficient R-wave triggering during mobilization of the heart.

OBJECTIVE: In order to achieve an accurate intraoperative ECG detection, a new technique in detecting the trigger-signal was developed. In contrast to the traditional three-lead ECG-configuration, the left leg electrode was connected to a transient epicardial pacemaker electrode on the left-ventricular surface. BACKGROUND DATA: The Holmium:YAG-Laser for Transmyocardial Laser Revascularization (TMLR) is R-wave-triggered, providing the release of energy only during the refractory period of the heart cycle. However, an exact ECG-triggering during mobilization of the apex and/or posterior wall is difficult to achieve by using conventional ECG-configuration, therefore increasing the risk for mistriggering and induction of arrhythmias during TMLR. MATERIALS AND METHODS: Two groups of patients, all undergoing stand alone TMLR-procedures via left minithoracotomy, were compared. Ten patients were operated with the conventional ECG configuration (group 1) and ten patients with the modified epicardial ECG configuration (group 2). RESULTS: In patients of group 1, as a result of a loss of the trigger signal or due to the triggering of artifacts, the incidence of correctly triggered QRS-complexes was 56% of all documented QRS-complexes. In contrast, an excellent triggering was observed in 98% (p < 0.001) in group 2, resulting in a reduction of laser operative time by 35% (p < 0.001) and a decrease in the incidence of intraoperative ventricular fibrillation (0 vs. 3). CONCLUSION: In conclusion, this new ECG configuration is a simple but effective method in achieving an excellent ECG signal during all stages of TMLR. As a consequence, a reduction in operative time and incidence of ventricular fibrillation can be achieved.