Fixed Rate Mode Research Articles

Effects of irradiation on the components of implantable pacemakers.

The purpose of this study was to examine the effects of irradiation on implantable pacemaker components. The pacemaker was divided into three components: lead wire and electrode, battery, and electrical circuit, and each component was irradiated by X-ray and electron beams, respectively. The pacemaker parameters were measured by both telemetry data of the programmer and directly measured data from the output terminal. The following results were obtained. For the lead wire and electrode, there was no effect on the pacemaker function due to irradiation by X-ray and electron beams. In the case of battery irradiation, there was no change in battery voltage or current up to 236Gy X-ray dose. In the electrical circuit, the pacemaker reverted to the regular beating rate (fixed-rate mode) immediately after the start of X-ray irradiation, and it continued in this mode during irradiation. In patients with their own heartbeat rhythm, changing to the fixed-rate mode may cause dangerous conditions such as ventricular fibrillation. When the accumulated irradiation dose is increased, another failure can be seen in the output voltage of the pacemaker. The pacing output voltage dropped rapidly by about 40 % at 30-88Gy. Decreasing the output voltage results in pacing disorders, and heart failure may occur. In the telemetry data of the programmer, no change in output voltage could be detected, highlighting the difference between telemetry data and actual pacing data.

Modeling Ventricular Function during Cardiac Assist: Does Time-Varying Elastance Work?

The time-varying elastance theory of Suga et al. is widely used to simulate left ventricular function in mathematical models and in contemporary in vitro models. We investigated the validity of this theory in the presence of a left ventricular assist device. Left ventricular pressure and volume data are presented that demonstrate the heart-device interaction for a positive-displacement pump (Novacor) and a rotary blood pump (Medos). The Novacor was implanted in a calf and used in fixed-rate mode (85 BPM), whereas the Medos was used at several flow levels (0-3 l/min) in seven healthy sheep. The Novacor data display high beat-to-beat variations in the amplitude of the elastance curve, and the normalized curves deviate strongly from the typical bovine curve. The Medos data show how the maximum elastance depends on the pump flow level. We conclude that the original time-varying elastance theory insufficiently models the complex hemodynamic behavior of a left ventricle that is mechanically assisted, and that there is need for an updated ventricular model to simulate the heart-device interaction.

INITIAL ANIMAL EXPERIMENT OF A LINEAR OSCILLATORY ACTUATOR DRIVEN VENTRICULAR ASSIST SYSTEM

The main purpose of this study is to develop an implantable direct electromagnetic left ventricular assist system (Linear-LVAS) with a linear oscillatory actuator (LOA). The Linear-LVAS is a pulsatile pump with a pusher-plate, which is driven directly by the mover of the LOA without any movement converter. The first model, developed in 2002, began its first animal experiment in 2003. The dimensions of the prototype Linear-LVAS are 100 mm in diameter, 50 mm in thickness, with a mass of 0.74 kg and a volume of 320 ml. The Linear-LVAS had two control algorithms: a fixed rate mode and a full-fill/full-eject mode (FFFE). Pump performance, long-term durability and nonthrombogenicity of Linear-LVAS was evaluated in a chronic animal experiment using a goat (56 kg). The goat survived for 42 days. The reason of termination of the experiment was the thrombus found in the pump. The maximum pump flow was around 4.2 L/min, with acceptable input power of 9 W. The maximum pump efficiency was 16.4%. Pump rate of Linear-LVAS driven by the FFFE control synchronized with goat’s heart rate. Pump housings and the diaphragm were free of major crack or deformation. Linear-LVAS had no troubles relating to the electronic control unit or the electronic drive line. There was no frictional dust found around the LOA in the pump unit. The experiment confirmed the durability of Linear-LVAS for 6 weeks.

Perioperative considerations in the patient with a left ventricular assist device.

Perioperative considerations in the patient with a left ventricular assist device.

Left ventricle assist systems: a possible alternative to heart transplantation for heart failure patients? Patient selection, techniques and benefit

Left ventricle assist systems: a possible alternative to heart transplantation for heart failure patients? Patient selection, techniques and benefit

Evaluation of an implantable motor-driven left ventricular assist device.

A console based implantable motor-driven left ventricular assist device (LVAD) was developed and tested. Ten sheep weighing 42-73 kg (mean, 54.4 kg) were used as the experimental animals. Four animals survived 5-12 h (mean, 9.5 h). The mean pump flow was 1.63 L/min, ranging from 0.8 to 2.5 L/min. The cause of termination was respiratory failure in 3 animals, bleeding in 2, ventricular fibrillation in 2, vent tube obstruction in 1, thrombus formation in 1, and mechanical failure of the driving console in 1. Following the in vivo studies, the computer regulated controller was tested in a mock circulatory system. The LVAD provided 5.34 L/min of maximum output against a mean afterload of 80 mm Hg with a filling pressure of 15 mm Hg when the pump rate was 80 bpm in the fixed rate mode. With an increase in the pump afterload from 80 to 140 mm Hg, the total system efficiency varied from 7.81 to 8.34% when the pump preload was 15 mm Hg. An ultracompact, completely implantable electromechanical VAD has been under development. This device should fit in a 60 kg adult. As the next step, we are preparing to implant this ultracompact implantable VAD with an electronic controller in an animal model with better results being expected.

Bethesda conference: conference for the design of clinical trials to study circulatory support devices for chronic heart failure

James M. Anderson, MD Eugene H. Blackstone, MD Harvey S. Boroevetz, PhD Arthur Ciarkowski, MD Jack G. Copeland III, MD Maria Rosa Costanzo-Nordin, MD Kurt Daase, MD Mary Amanda Dew, PhD Michael J. Domanski, MD Benjamin H. Eidleman, MD Roger W. Evans, PhD David J. Farrar, PhD O. H. Frazier, MD Bartley P. Griffith, MD Charles-Julien Hahn, MD J. Donald Hill, MD Sharon Hunt, MD Kay Kendell, RN Robert L. Kormos, MD Howard R. Levin, MD Donna M. Mancini, MD Patrick M. McCarthy, MD Dennis McNamara, MD Fr Kevin O’Rourke, PhD Lisa Parker, PhD D. Glenn Pennington, MD Victor L. Poirier, PhD Peer M. Portner, PhD Eric A. Rose, MD Wolf Sapirstein, MD Eleanor Schron, MD Rhona Shanker, MD Ramiah Subramanian, MD John Wallwork, MD Lynne Warner Stevenson, MD

Perfusion/ventilation mismatch during exercise in chronic heart failure: an investigation of circulatory determinants.

The ventilatory cost of carbon dioxide (CO2) elimination on exercise (VE/VCO2) is increased in chronic heart failure (CHF). This reflects increased physiological dead space ventilation secondary to mismatching between perfusion and ventilation during exercise. The objectives of this study were to investigate the relation of this increased VE/VCO2 slope to the syndrome of CHF or to limitation of the exercise related increase of pulmonary blood flow, or both. Maximal treadmill exercise tests with respiratory gas analysis were performed in 45 patients with CHF (defined as resting left ventricular ejection fraction < 40% on radionuclide scan); 15 normal controls; 23 patients with coronary artery disease and normal resting left ventricular function; and 13 pacemaker dependent patients (six with and seven without CHF) directly comparing exercise responses in rate responsive and fixed rate mode. Patients with CHF had a steeper VE/VCO2 slope than normal controls: this was related inversely to peak VO2 below 20 mol/min/kg. In patients with coronary artery disease in whom peak VO2 (at respiratory exchange ratio > 1) was as limited as in the patients with CHF but resting left ventricular function was normal, the VE/VCO2 slope was normal. In pacemaker dependent patients fixed rate pacing resulted in lower exercise capacity and peak VO2 than rate responsive pacing; the VE/VCO2 slope was normal in patients without CHF but steeper than normal in patients with CHF; the VE/VCO2 slope was steeper during fixed rate than during rate responsive pacing in these patients with CHF. These findings suggest that the perfusion/ventilation mismatch during exercise in CHF is related to the chronic consequences of the syndrome and not directly to limitation of exercise related pulmonary flow. Only when the syndrome of CHF is present can matching between perfusion and ventilation be acutely influenced by changes in pulmonary flow.

Small soft left ventricular assist device powered by intraaortic balloon pump console for infants: a less expensive option.

We have developed a pneumatically driven 20 cc soft ventricle for temporary right, left, or biventricular assist. The ventricle consists of a vacuum-formed soft housing, diaphragm, tricuspid outflow valve, and biflap inflow valve. All components including inflow and outflow valves were made with Pellethane. The advantages of this blood pump are as follows: it eliminates use of the quick connect system and therefore is less thrombogenic; the biflap inflow valve provides low inflow resistance; the soft ventricle is easy to implant; the polyurethane valves eliminate blood damage and thromboembolism and are low in cost compared with mechanical valves; and the vacuum-forming technique is reliable, fast, capable of mass production, and therefore inexpensive. We have already demonstrated in both in vitro and in vivo experiments that this ventricle has excellent hemodynamic performance with less blood damage and thrombogenesis. In this study, we evaluated the possible application of a well-defined and widely distributed intraaortic balloon pump (IABP) console to the 20 cc left ventricular assist device (LVAD) driver. The pump was tested in 6 mongrel dogs (6 to 10 kg) using an IABP console. The pump was connected between the left atrium and the ascending aorta, placed paracorporeally on the chest wall, and driven at a synchronous or fixed rate mode without using vacuum. The 20 cc ventricle could maintain the same output as the control output of the natural heart at filling pressures of 5 to 10 mm Hg during the entire observation time of 5 h. Thus, this 20 cc soft ventricle has the potential to be widely used for the treatment of severe heart failure in infants because of its excellent hemodynamic performance, simplicity, and low cost.

Development of totally implantable electromechanical artificial heart systems: Baylor ventricular assist system.

An implantable electromechanical ventricular assist system (VAS) intended for permanent use has been developed. It consists of a conically shaped pumping chamber, a polyolefin (Hexsyn) rubber diaphragm attached to a conically shaped pusher-plate, and a compact roller-screw actuator. Design stroke volume is 63 ml. The device weighs 620 g, and has a total volume of 348 ml. The pump can provide 8 L/min flow against 120 mm Hg afterload with a preload of 10 mm Hg. The inner surfaces are biolized by dry gelatin coating, with inflow and outflow ports accommodating tissue valves. Three subacute in vivo validation studies have been conducted in calves up to two weeks. The entire system functioned satisfactorily in both the fill/empty and the fixed-rate modes. There was no thromboembolic complication without anticoagulation. The pump showed reasonable anatomical fit inside the left thorax. This VAS is compact, efficient, quiet, and easy to control.

A biolized implantable ventricular assist device compatible with IABP console.

A low pressure pneumatic pusher plate blood pump was developed for temporary right, left, or biventricular assist. Important features of this pump are its 1) driveability by the standard, easily available intraaortic balloon pump (IABP) console; 2) gelatin coated internal surface for blood compatibility; 3) essentially flat disc shape, 3 cm thick and 11 cm in diameter, for optimal anatomic fit; and 4) unique pusher plate guide mechanism to ensure linear motion without deflections of the diaphragm, and consequent uniform flow distribution into the pump. The guide telescopes into itself to avoid a housing protrusion for easy implantability; this controlled movement also provides a number of performance, control, and diagnostic benefits. The pump's 60 ml displacement gives up to 4.7 L/min at 80 bpm and 6.7 L/min at 120 bpm outputs in a mock loop. This VAD has been implanted in two calves for 43 to 84 days, continuously driven by a Datascope IABP console. An average 5 L/min pump output has been observed in both synchronous and fixed rate modes. No anticoagulation was required. We expect extensive clinical use of this VAD, based on its reliability, low cost, and simplicity.

A Biolized Implantable Ventricular Assist Device Compatible with IABP Console

A low pressure pneumatic pusher plate blood pump was developed for temporary right, left, or biventricular assist. Important features of this pump are its 1) driveability by the standard, easily available intraaortic balloon pump (IABP) console; 2) gelatin coated internal surface for blood compatibility; 3) essentially flat disc shape, 3 cm thick and 11 cm in diameter, for optimal anatomic fit; and 4) unique pusher plate guide mechanism to ensure linear motion without deflections of the diaphragm, and consequent uniform flow distribution into the pump. The guide telescopes into itself to avoid a housing protrusion for easy implantability; this controlled movement also provides a number of performance, control, and diagnostic benefits. The pump's 60 ml displacement gives up to 4.7 L/min at 80 bpm and 6.7 L/min at 120 bpm outputs in a mock loop. This VAD has been implanted in two calves for 43 to 84 days, continuously driven by a Datascope IABP console. An average 5 L/min pump output has been observed in both synchronous and fixed rate modes. No anticoagulation was required. We expect extensive clinical use of this VAD, based on its reliability, low cost, and simplicity.

Extended clinical support with an implantable left ventricular assist device.

Clinical evaluations are under way of an intracorporeal (abdominally positioned) pulsatile left ventricular assist device (LVAD) that is capable of providing support for extended periods (greater than 30 days) in patients awaiting heart transplantation. The LVAD, developed by Thermo Cardiosystems Inc. (Woburn, MA), has uniquely textured blood contacting surfaces and requires only minimal antithrombotic therapy. It has been used at the Texas Heart Institute as a bridge to transplantation in 11 patients, including 2 who are currently receiving support. Four patients required extended LVAD support (35-132 days); of those, three are doing well at 1.5, 8.5, and 13 months, respectively, after transplantation, and one died of liver failure 49 days after transplantation. The LVAD was operated in a fixed-rate mode to maintain pump flows at 4-8 L/min, resulting in stabilization of hemodynamic and secondary organ function in all patients. Blood chemistry and hematologic values returned to normal during LVAD support in three of four patients. Postoperative anticoagulation was gradually reduced over the course of the trials. The two most recent patients (35 and 132 days) received only oral dipyridamole (75 mg X 3/day) and aspirin (80 mg/day) after the early recovery period (four-six days), resulting in normal prothrombin and partial thromboplastin times. Plasma hemoglobin levels remained within acceptable limits, and there was no evidence of thromboembolism. Blood contacting surfaces were coated with a thin, adherent, biologically derived lining. The initial results indicate that the intracorporeal LVAD, with textured blood contacting surfaces, can effectively support the failing heart for extended periods (greater than 30 days) with minimal antithrombotic therapy.

Safety precautions in the management of patients with pacemakers when electrocautery operations are performed : Erdman S, Levinsky L, Servadio C, et al: Surg Gynecol Obstet 167:311–314, 1988

The hazards related to ten patients who underwent 11 urologic surgical procedures during a 36 month period were taken into consideration. Electrocautery was used in all instances and there were no complications. All of the pacemakers were preset for ventricular pacing and sensing inhibited or multiprogrammable and were reprogrammed during the operation to ventricular pacing fixed rate mode or magnet mode, with very satisfactory outcome. To avoid life-threatening situations arising from pacemaker inhibition or ventricular fibrillation during cautery for transuretheral resection, three basic factors were considered: 1, appropriate type of pacemaker; 2, the proper grounding of all medical electronic equipment used during the procedure, and 3, the directing of the complete flow of the electrocautery circuits substantially below the level of the pacemaker unit.

Variations in discharge rate of demand pacemakers not due to malfunction

Demand pacemakers may have variations in discharge rate which are not due to malfunction. Physiologic changes of intraventricular conduction can cause implanted ventricular units to sense earlier or later during the QRS interval and therefore discharge so as to produce a different R-R interval. Furthermore, if the patient's own ventricular rate exceeds the pacer's escape rate, demand pacing will not occur. Because of such features, demand units should be regularly tested in a continuous (fixed-rate) mode produced by application of an external magnet. The rate of the induced continuous mode will always by design exceed the escape rate in the demand mode. External demand pacers discharge more slowly in the demand than in the fixed-rate mode as a function of the interval from the pacemaker spike to the peak of the corresponding R wave which is sensed by the demand pacemaker circuit. The decreased heart rate is particularly striking with temporary atrial pacing, where the beat to beat interval is lengthened by the interposition of the P-R segment. Electrocardiograms from illustrative cases are presented to demonstrate these phenomena. The physician should be aware that variations in pacer discharge rate in the demand mode and between demand and continuous pacing are not necessarily due to pacemaker malfunction, but are rather inherent features of normal demand pacemaker operation.

Intrapericardial pacemaking: A preliminary report

Intrapericardial pacing is a new and simple echnique of electrode placement for the long term correction of complete heart block. It requires the application of a specially designed electrode to the diaphragmatic surface of the parietal pericardium in contact with the inferior surface of the heart. A study in dogs established the feasibility of this type pacing for synchronous, standby and fixed rate modes of electrical stimulation. The first implant was performed on August 10, 1967. Thirteen patients were treated. Pacing was asynchronous in 10, synchronous in two and in one, pacing was not attempted because of technical factors. Long term pacing was maintained in nine patients. Three of the nine required corticosteroid therapy to overcome interference by post-operative pericarditis. A pervenous or myocardial system was substituted for intrapericardial pacing which failed early after surgery in three patients with adhesive pericarditis or pericardial effusion. It is the author's opinion that this is a valuable alternate or primary method for pacing. Its advantages include: 1) a simple safe operative approach, 2) a stable electrode fixation, 3) avoidance of ventricular muscle trauma and 4) minimal electrode motion resulting in less possibility of electrode breakage.