PubMed Health⌕ Search

Biomedical subjects

H R Levin

Publications and source records attributed to H R Levin.

53 records · Page 3Linked to original sources
PubMed1994

Malignant ventricular arrhythmias are well tolerated in patients receiving long-term left ventricular assist devices.

OBJECTIVES: We sought to quantitate the incidence of malignant ventricular arrhythmias and to identify subsequent hemodynamic changes and untoward events in patients who have received an implantable left ventricular circulatory assist device as an extended bridge to heart transplantation. BACKGROUND: Implantable long-term mechanical circulatory assist devices have been used clinically with increasing frequency and success for the past 4 years. Previous investigators have suggested that patients with malignant ventricular arrhythmias receiving a left ventricular assist device will require both left and right ventricular assistance to maintain vital organ perfusion. METHODS: We reviewed our 4-year experience with 21 patients who underwent implantation of a left ventricular assist device. Device flows and mean arterial pressure were used to assess systemic perfusion; central venous pressure provided a gauge of right ventricular function. Charts were screened for evidence of end-organ injury resulting from malignant ventricular arrhythmias. RESULTS: Malignant ventricular arrhythmias occurred in 4 patients (19%) before device placement and in 9 patients (43%) during device support. The latter nine patients formed the final study group; their arrhythmias occurred 0 to 186 days after device implantation and had a duration of 10 min to 12 days. The patients reported weakness or palpitation; however, none reported syncope or dyspnea. Mean arterial pressure and central venous pressure were insignificantly changed by the arrhythmias. Device flow decreased by 1.4 +/- 0.6 liters/min (p < 0.05) at the onset of the arrhythmias but returned to normal after cardioversion. No thromboembolic events or significant end-organ dysfunction occurred. CONCLUSION: Absence of right ventricular contraction during malignant ventricular arrhythmias is well tolerated in recipients of a left ventricular assist device. The diagnosis of malignant arrhythmia should be suspected if an unexplained decrease in left ventricular assist device flow occurs. Early electrical cardioversion is warranted to avoid both thrombus formation in the native heart and right ventricular myocardial injury from prolonged fibrillation.

Adolescent↗
PubMed1994

Artificial circulatory support with textured interior surfaces. A counterintuitive approach to minimizing thromboembolism.

BACKGROUND: Although numerous left ventricular assist devices (LVADs) have been used clinically, frequent thromboembolic complications have been reported despite the smooth interior LVAD surfaces and systemic anticoagulant medication. In contrast, the Thermo Cardiosystems HeartMate 1000 IP LVAD has textured interior surfaces that are promptly covered by a densely adherent neointima. We hypothesize that elimination of a direct interface between prosthetic material and blood elements reduces the risk of peripheral embolization and minimizes the necessity for systemic anticoagulant medication. This report defines the thromboembolic risk of this type of LVAD and characterizes the nature and effectiveness of the various anticoagulation regimens that were tested during the initial clinical trial with this device. METHODS AND RESULTS: All values are reported as mean +/- SD. Fifty-four males and three females with an average age of 47 +/- 11 years were supported with the HeartMate 1000 IP LVAD for an average of 62 +/- 76 days at 11 clinical centers in the United States. Patients were prospectively evaluated for thromboembolic complications. Five different anticoagulation regimens were used during the first 4 postoperative weeks: no anticoagulants, low-molecular-weight dextran, heparin, dipyridamole plus aspirin, or miscellaneous agents. After the first 4 weeks, the patients were treated with aspirin plus dipyridamole or miscellaneous agents. Prothrombin time (PT), partial thromboplastin time (PTT), and fibrinogen values for the patients were measured at 0.1, 1, 2, 4, 8, 12, 16, 20, 24, 32, and 46 weeks during support. Two patients (3.5%) suffered thromboembolic cerebrovascular complications, an incidence of 0.2 episodes per patient-year of observation. One episode was due to fungal vegetation developing on the device and the other was due to embolization from a previously placed native mechanical aortic valve prosthesis. In the absence of infection, there were no device-related thromboembolic complications. Mean prothrombin time for all groups was 13.3 +/- 0.5 seconds with no significant intergroup differences. Mean partial thromboplastin time during the first 4 weeks for the heparin-treated group was 53.3 +/- 6.6 seconds, which was significantly longer than for all other groups, but fell to control values after heparin was discontinued at 4 weeks. Mean fibrinogen level for all groups was 370 +/- 48 mg/dL, with no intergroup differences. CONCLUSIONS: The HeartMate 1000 IP LVAD provides adequate circulatory support with a low risk of thromboembolism despite minimal systemic anticoagulation. The use of textured surfaces may be an important factor contributing to the low observed risk of thromboembolic complications.

Anticoagulants↗
PubMed1994

Technique for removal of left ventricular assist devices.

As the use of long-term implantable left ventricular assist devices increases, more surgeons will be required to remove the devices for transplantation or in the event of infection. We outline several maneuvers that facilitate device removal and several pitfalls that complicate the procedure. Important considerations include preventive measures at the time of device implantation and prevention of air embolism.

Embolism, Air↗
PubMed1993

A preliminary study of cardiopulmonary resuscitation by circumferential compression of the chest with use of a pneumatic vest.

BACKGROUND: More than 300,000 people die each year of cardiac arrest. Studies have shown that raising vascular pressures during cardiopulmonary resuscitation (CPR) can improve survival and that vascular pressures can be raised by increasing intrathoracic pressure. METHODS: To produce periodic increases in intrathoracic pressure, we developed a pneumatically cycled circumferential thoracic vest system and compared the results of the use of this system in CPR (vest CPR) with those of manual CPR. In phase 1 of the study, aortic and right-atrial pressures were measured during both vest CPR (60 inflations per minute) and manual CPR in 15 patients in whom a mean (+/- SD) of 42 +/- 16 minutes of initial manual CPR had been unsuccessful. Vest CPR was also carried out on 14 other patients in whom pressure measurements were not made. In phase 2 of the study, short-term survival was assessed in 34 additional patients randomly assigned to undergo vest CPR (17 patients) or continued manual CPR (17 patients) after initial manual CPR (duration, 11 +/- 4 minutes) had been unsuccessful. RESULTS: In phase 1 of the study, vest CPR increased the peak aortic pressure from 78 +/- 26 mm Hg to 138 +/- 28 mm Hg (P < 0.001) and the coronary perfusion pressure from 15 +/- 8 mm Hg to 23 +/- 11 mm Hg (P < 0.003). Despite prolonged unsuccessful manual CPR, spontaneous circulation returned with vest CPR in 4 of the 29 patients. In phase 2 of the study, spontaneous circulation returned in 8 of the 17 patients who underwent vest CPR as compared with only 3 of the 17 patients who received continued manual CPR (P = 0.14). More patients in the vest-CPR group than in the manual-CPR group were alive 6 hours after attempted resuscitation (6 of 17 vs. 1 of 17) and 24 hours after attempted resuscitation (3 of 17 vs. 1 of 17), but none survived to leave the hospital. CONCLUSIONS: In this preliminary study, vest CPR, despite its late application, successfully increased aortic pressure and coronary perfusion pressure, and there was an insignificant trend toward a greater likelihood of the return of spontaneous circulation with vest CPR than with continued manual CPR. The effect of vest CPR on survival, however, is currently unknown and will require further study.

Aorta↗
PubMed1993

Pressure-volume analysis of changes in cardiac function in chronic cardiomyoplasty.

Reports of clinical improvement in human studies of dynamic cardiomyoplasty lack support by consistent objective hemodynamic evidence. Animal studies have also yielded conflicting results, likely due to nonuniform models, particularly the use of unconditioned wraps, and to limitations in commonly used study modalities caused by exaggerated heart motion during wrap stimulation. Our purpose was to assess the primary functional properties of the heart wrapped by conditioned muscle using pressure-volume relation analysis based on conductance catheter volume data. Compared with the unstimulated state, 1:1 stimulation caused an increase in contractility and decreases in end-diastolic volume and stroke work. Assisted beats during 1:2 stimulation showed an increase in contractility and a decrease in end-diastolic volume. Unassisted beats (1:2) showed decreases in end-diastolic volume and stroke work. There was no augmentation of cardiac output or ejection fraction with stimulation (1:1 or 1:2). We conclude that in the nonfailing heart, increased contractility does not augment cardiac output, ejection fraction, and stroke work because of a simultaneous decrease in end-diastolic volume. These changes in contractility and end-diastolic volume may prove therapeutic for dilated cardiomyopathy.

Animals↗
PubMed1991

Optimization of the timing of skeletal to cardiac muscle contraction during dynamic cardiomyoplasty: analysis using a mathematical model.

Cardiomyoplasty, or the use of skeletal muscle to assist the failing heart, has been studied for many years but has enjoyed only minimal success. It has been suggested that a delay in the start of skeletal muscle contraction relative to the QRS complex would enhance aortic flow. To study the effects of simulated changes in the relative timing of skeletal muscle contraction, heart rate and skeletal muscle contraction duration, a mathematical model was used to predict the vascular pressures and flows during cardiomyoplasty. The vascular pressures and cardiac output generated by the model for both the normal and heart failure state were similar to previously published canine data. Skeletal muscle contraction synchronous with cardiac mechanical systole (i.e., delayed approximately 50-75 ms from the QRS) was able to provide improvements in cardiac output, arterial blood pressure and aortic flow velocity up to 40% over the baseline heart failure state. A delay in the start of skeletal muscle contraction, prolonged skeletal muscle contraction duration or an increase in the heart rate from 90 to 120/min reduced this benefit. Thus, mechanical synchrony of skeletal and cardiac muscle contraction optimizes hemodynamics during cardiomyoplasty.

Heart Failure↗
PubMed1986

Determinants of blood flow to vital organs during cardiopulmonary resuscitation in dogs.

Whether blood flow during cardiopulmonary resuscitation (CPR) results from intrathoracic pressure fluctuations or direct cardiac compression remains controversial. From modeling considerations, blood flow due to intrathoracic pressure fluctuations should be insensitive to compression rate over a wide range, but dependent on the applied force and compression duration. If direct compression of the heart plays a major role, however, flow should be dependent on compression rate and force, but above a threshold, insensitive to compression duration. These differences in hemodynamics produced by changes in rate and duration form a basis for determining whether blood flow during CPR results from intrathoracic pressure fluctuations or from direct cardiac compression. Manual CPR was studied in eight anesthetized, 21 to 32 kg dogs after induction of ventricular fibrillation. There was no surgical manipulation of the chest. Myocardial and cerebral blood flows were determined with radioactive microspheres. At nearly constant peak sternal force (378 to 426 newtons), flow was significantly increased when the duration of compression was increased from 14 +/- 1% to 46 +/- 3% of the cycle at a rate of 60/min. Flow was unchanged, however, after an increase in rate from 60 to 150/min at constant compression duration. The hemodynamics of manual CPR were next compared with those produced by vest inflation with simultaneous ventilation (vest CPR) in eight other dogs. Vest CPR changed intrathoracic pressure without direct cardiac compression, since sternal displacement was less than 0.8 cm. At a rate of 150/min, with similar duration and right atrial peak pressure, manual and vest CPR produced similar flow and perfusion pressures. Finally, the hemodynamics of manual CPR were compared with the hemodynamics of direct cardiac compression after thoracotomy. Cardiac deformation was measured and held nearly constant during changes in rate and duration. As opposed to changes accompanying manual CPR, there was no change in perfusion pressures when duration was increased from 15% to 45% of the cycle at a constant rate of 60/min. There was, however, a significant increase in perfusion pressures when rate was increased from 60 to 150/min at a constant duration of 45%. Thus, vital organ perfusion pressures and flow during manual external chest compression are dependent on the duration of compression, but not on rates of 60 or 150/min. These data are similar to those observed for vest CPR, where intrathoracic pressure is manipulated without sternal displacement, but opposite of those observed for direct cardiac compression.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Elastic properties of the human chest during cardiopulmonary resuscitation.

Sternal displacement during CPR was measured in 11 adults and 2 manikins (Recording Resusci Anne) while the chest was compressed with variable maximum pulse compression force at a rate of 60/min with compression duration of 0.5-0.6 sec. In 10 patients, the pulsatile sternal elastic characteristic can be satisfactorily described with a 2nd degree polynomial F = beta Ds + gamma D2s, where beta = 54.9 +/- 29.4 (mean +/- SD) N/cm is the pulsatile initial elasticity and gamma = 10.8 +/- 4.1 N/cm2 is the posterior resiliency. The sternal characteristics of manikins were linear F = kDs with high elasticity constants, k = 131 and 142 N/cm. Therefore, the manikins tested differ significantly in elasticity characteristics from the human chest during resuscitation. In general, the manikin: (1) has markedly greater stiffness at the onset of compression, and (2) maintains a linear stiffness throughout the usual range of displacement, rather than becoming stiffer with greater chest displacement.

Adolescent↗
PubMedDate not supplied

Intravascular ultrasound imaging of the Heartmate 1000 IP left ventricular assist device.

Left ventricular assist devices are increasingly used as a bridge to transplantation in patients with end-stage cardiac disease. Potential complications of these devices include thromboembolism and infection. Because conventional cardiac diagnostic techniques cannot be used to obtain an image of the interior of a left ventricular assist device, we assessed the ability of intravascular ultrasonography to obtain an image of the interior of the Heartmate 1000 IP left ventricular assist device. Feasibility of intravascular ultrasound imaging was initially demonstrated in vitro on a left ventricular assist device immersed in water. Five soft rubber masses were then placed in the device intake port adherent to the wall, and their images were obtained by intravascular ultrasonography. Excellent correlation between actual size and size as measured by intravascular ultrasonography was noted (long-axis, r = 0.98, short-axis, r = 0.89). After the device was implanted in two calves, intravascular ultrasound imaging was performed in vivo in the animals. The catheter was easily advanced through the device, and excellent images were obtained. In conclusion, intravascular ultrasonography can easily be used to obtain an image of the left ventricular assist device interior and can accurately assess the presence and size of abnormal masses inside the device. Intravascular ultrasonography may be clinically useful in evaluating cases of thrombus or vegetation related to left ventricular assist devices.

Animals↗
PubMedDate not supplied

Comparison of rejection in the atrioventricular node and bundles with the working myocardium in transplanted hearts.

At present the monitoring of heart transplant patients for rejection is done by endomyocardial biopsy. It has been proposed that ECG assessments of conduction delay may provide a noninvasive means of detecting rejection. To determine whether rejection in the atrioventricular node and conduction bundles reflects rejection in the working myocardium, we studied 21 transplanted hearts from 21 cardiac allograft recipients. Twenty of the hearts were obtained at autopsy, and one was obtained from a patient who underwent a second transplant procedure. The atrioventricular conduction tissues, the ventricular and atrial free walls, and the interventricular and interatrial septa from these hearts were examined for histologic evidence of rejection. Of the 21 hearts, 17 showed histologic changes of acute allograft rejection. Of the 17, rejection involved the conducting system and the myocardium equally in 11. In 6 of the 17 hearts, rejection involved the working myocardium more severely than it did the conducting system. Of interest, nonrejection pathologic changes were also noted in the conducting systems of several hearts. Severe accelerated arteriosclerosis was found in the artery to the atrioventricular node in one case, and lesser degrees of accelerated arteriosclerosis in this artery were found in two additional cases. In one case, lymphoid infiltrates, consistent with posttransplant lymphoproliferative disorder, were noted in the vicinity of the atrioventricular node, and several hearts demonstrated operative trauma or ischemic changes that appeared to involve the conducting system. These results suggest that although there may be a morphologic basis for using electrophysiologic changes in the conducting system to monitor heart allograft recipients for rejection, caution should be exercised in interpreting these changes.

Adult↗
PubMedDate not supplied

Desaturated venous-to-arterial shunting reduces right-sided heart failure after cardiopulmonary bypass.

BACKGROUND: Right-sided circulatory failure is a major cause of morbidity in heart transplant and ventricular assist device recipients. METHODS: Several systems for managing right-sided circulatory failure with use of a right-to-left shunt without need for an oxygenator or systemic heparinization were designed and used clinically. RESULTS: A right-to-left shunt was successfully used to treat severe right-sided circulatory failure in both a transplant and a left ventricular assist device recipient. CONCLUSIONS: If constructed between the femoral vein and artery, such a shunt could (1) be easily inserted and removed, (2) selectively infuse the lower extremities with desaturated blood while maintaining cerebral and cardiac perfusion with saturated blood, (3) selectively reduce the risk of paradoxical emboli to the head and heart, and (4) provide a known and adjustable degree of shunting depending on the condition of the patient, a major advantage of this system compared with creation of an atrial septal defect.

Cardiopulmonary Bypass↗
PubMedDate not supplied

Use of a pulsatile right ventricular assist device and continuous arteriovenous hemodialysis in a 57-year-old man with a pulsatile left ventricular assist device.

BACKGROUND: Despite advances in the perioperative treatment of both heart transplant and left ventricular assist device recipients, right-sided circulatory failure refractory to medical management remains a major source of morbidity in the immediate postoperative period. In addition, hypervolemia is a frequent complication encountered in the treatment of these patients because of their large fluid intake requirements and relative potential for kidney failure. METHODS: Previous reports have documented the use of continuous-flow devices to support the failing right-sided circulation of patients after both left ventricular assist device insertion and orthotopic heart transplantation. However, such continuous-flow devices may carry the attendant risks of hemolysis and bleeding and may further require 24-hour monitoring by trained personnel. We report the temporary-use pulsatile Abiomed BVS 5000 right ventricular assist device and continuous arteriovenous hemodialysis in the recipient of a pulsatile TCI HeartMate 1000 IP left ventricular assist device both after left ventricular assist device implantation and after orthotopic heart transplantation. RESULTS: The patient was well at 13 months follow-up. CONCLUSIONS: The use of right ventricular assist devices and continuous arteriovenous hemodialysis in both transplant and left ventricular assist device recipients undoubtedly will remain important as the popularity of these two therapeutic modalities continues to grow.

Equipment Design↗
PubMedDate not supplied

Complications of endomyocardial biopsy in heart transplant patients.

Despite the increasing use of alternative techniques, endomyocardial biopsy remains the primary method for diagnosing cardiac allograft rejection. Improved patient longevity and an increasing number of transplantation centers are resulting in an increase in the number of biopsies performed. Although endomyocardial biopsy is usually considered a safe procedure, no large studies of the risks of endomyocardial biopsy specifically in the transplant population have been undertaken. To determine the risk of endomyocardial biopsy in these patients, we reviewed 2454 endomyocardial biopsies performed from January 1983 to December 1990 in 133 cardiac allograft patients at our institution. At the time of each endomyocardial biopsy, a worksheet was completed detailing the patient's interval history, the site of vascular introduction, the number of attempts, the number of specimens, and any complications encountered. A total of 74 (3.0%) complications occurred. Fifty-six (2.3%) complications were associated with catheter insertion, including carotid puncture (1.8%), vasovagal reaction (0.1%), and prolonged bleeding (0.4%). Complications during biopsy included arrhythmias (0.25%) and conduction abnormalities (0.2%). In addition, we observed five episodes (three patients) of allergic reaction to a reusable bioptome and one case of pacemaker dislodgement. All complications were without significant long-term sequelae. In contrast to the cardiomyopathy population, no ventricular perforations or deaths occurred. Thus although endomyocardial biopsy has some risk, it continues to be a safe and effective way of monitoring rejection.

Adult↗
PubMedDate not supplied

Fungal infections in left ventricular assist device recipients. Incidence, prophylaxis, and treatment.

The authors reviewed the charts of 26 recipients of a left ventricular assist device to determine the incidence of fungal infections and the clinical course of these patients. Nine patients (35%) had positive fungal cultures. Of these, six had clinical infections and three were colonized asymptomatically. Three of the six infected patients (including one with mediastinal sepsis and another requiring left ventricular assist device replacement for intractable fungemia) underwent orthotopic heart transplantation after successful therapy. Of the remaining three, one died of a thromboembolic stroke (probably septic in nature), one died secondary to driveline rupture, and the third succumbed to culture-negative sepsis. Two of the colonized patients underwent transplantation, and the third succumbed to perioperative right sided circulatory failure and hypoxia. Positive fungal cultures were a common finding in our series. Because of a significant incidence of fungal infection-related morbidity, the authors revised their pre operative and post operative protocol to include: 1) 2 weeks of fluconazole therapy (200 mg intravenously daily) for patients receiving broad spectrum antibiotics and for those with evidence of preoperative fungal colonization; 2) daily dressing changes around drivelines; 3) daily nystatin swish and swallow; and 4) empiric fluconazole treatment for culture-negative sepsis. Using this protocol, three left ventricular assist device recipients received prophylactic fluconazole and had no evidence of fungal morbidity or mortality on short-term follow-up.

Adult↗
PubMedDate not supplied

Gastrointestinal consequences of left ventricular assist device placement.

Left ventricular assist devices effectively improve hemodynamic function and reverse renal and hepatic dysfunction; however, their effects upon the gastrointestinal (Gl) system have not been addressed. We evaluated Gl function in 27 left ventricular assist device recipients using interviews, Gl contrast studies, endoscopy, and 99mTc sulfur colloid studies of esophageal transit and gastric emptying. While on left ventricular assist device support (mean duration of 84 days), 19 patients reported early satiety and/or nausea, and 1 was unable to tolerate oral intake. Esophageal transit time (normal, < 10 sec) was borderline slow at 14 +/- 4 (mean +/- standard error of the mean) and gastric emptying (normal < 90 min) was prolonged (range of 106-506 min, mean = 283 +/- 69 min). In a 1-38 month follow-up, gastric function subjectively improved in all. Six patients had intraperitoneal device placement. One died of aspiration pneumonia secondary to small bowel obstruction, and one had prolonged inability to tolerate oral intake, which required feeding jejunostomy tube placement. The 21 patients with pre peritoneal placement of the device did not require Gl operative interventions and had no catastrophic Gl events; they had mild to no Gl complaints. Pre peritoneal placement may mitigate early satiety and obviate serious Gl complications.

Digestive System Physiological Phenomena↗