Importance of AV synchronous pacing during low intensity exercise evaluated by oxygen kinetics.

It has been shown that dual chamber pacing with preservation of AV synchrony (DDD) is superior to fixed rate ventricular (VVI) or rate responsive ventricular (VVIR) pacing modes, as evaluated by ventilatory response to exercise. Previous studies have focused on the benefits of maintained AV synchrony at maximal exercise. However, there are limited data comparing O2 kinetics in different pacing modes during low intensity exercise, representing the majority of daily activities. This study aimed to provide an evaluation of different pacing modes using O2 kinetics during low intensity exercise. Nineteen patients (age 61 +/- 18 years) with complete AV block underwent low intensity treadmill exercise (35 W) with simultaneous evaluation of symptoms and O2 kinetics in three pacing modes. The first test was performed in DDD mode followed by a second test in VVIR mode with a programmed heart rate corresponding to the sinus rate during the first test. After 6 minutes of each test, the mode was switched from DDD to VVIR and vice versa. The third test was performed in VVI mode at 70 beats/min. O2 kinetics were defined as O2 deficit (time [rest to steady state] x delta VO2-sigma VO2 [rest to steady state]) and mean response time (MRT) of oxygen consumption (O2 deficit/delta VO2). The O2 deficit was 551 +/- 134 mL in DDD pacing, 634 +/- 139 mL in VVIR pacing, and 648 +/- 179 mL in VVI pacing (P = 0.001). MRT was 49 +/- 7.8 seconds in DDD pacing, 54.7 +/- 9.5 seconds in VVIR pacing, and 57.4 +/- 11.0 seconds in VVI pacing (P = 0.002). Ten (53%) patients developed symptoms during switch from DDD to VVIR mode whereas the switch from VVIR to DDD mode was not perceived by any patient (P < 0.001). In conclusion, our study shows an impact of AV synchronous pacing and heart rate adaptation on O2 kinetics during low intensity exercise that correspond to casual daily life activities. Our observations may have clinical implications for the management of patients with complete AV block.

Age and sex related changes in heart rate to ventilation coupling: implications for rate adaptive pacemaker algorithms.

Minute ventilation (VE) controlled rate adaptive pacemakers determine the paced rate increase during exercise by measuring changes in transthoracic impedance that have been shown to correlate well with VE. To determine the normal coupling of heart rate (HR) to VE this relationship was evaluated in 30 younger and 25 older, healthy subjects using peak cardiopulmonary exercise testing. After determining the anaerobic threshold (AT), the linear HR to VE slope was determined both below and above the AT. In addition, the entire curve of the HR to VE relationship was assessed by a "best fit" regression analysis method. The relationship of HR to VE was more often logarithmic in younger as compared to older subjects. The HR to VE slope below the AT was always steeper than above the AT in younger subjects. Females of both age subgroups demonstrated a significantly greater slope below and above the AT. For the appropriate programming of VE controlled, rate responsive pacemakers, one should take into consideration age- and sex-specific differences in the HR to VE relationship throughout exercise. Therefore, age- and sex-specific programmable features for rate responsive parameters should be incorporated into pacemakers using VE controlled rate adaptive algorithms.

Premature ICD battery depletion due to a defective lead adapter component: usefulness of extensive data logging.

Described herein is the usefulness of extensive data logging of third generation ICDs in a patient with premature ICD battery depletion due to a defective pace/sensing lead component. Due to noise artifacts, VT/VF detections occurred leading to inappropriate patient shock discharges and 2,267 internal charge dumps within 2 weeks. During manual manipulations at the ICD site, real-time intracardiac electrocardiogram and event markers revealed noise artifacts that were interpreted as VT/VF. Radiography confirmed slight movement of the pace/sensing lead pin out of the Y-adapter. Therefore, the design of adapter systems without screw fixation should be reviewed to ensure lead integrity. In the case of sudden increases in VT/VF recognition, defective sensing components must be considered.

Histologic evidence of angiographic catheter-induced vascular trauma: a comparison of conventional and deformable soft-tip catheters.

Catheter-related complications associated with coronary arteriography remain an iatrogenic hazard with life-threatening consequences. Because such complications may be related to catheter-tip-induced vascular trauma during coronary angiography or percutaneous transluminal coronary angioplasty (PTCA), several types of deformable, soft-tip angiographic catheters have been developed. The following study was undertaken to evaluate the effects of one of these catheters, as well as of conventional catheters, in canine arteries. Ten dogs were catheterized, five with a conventional angiographic catheter and five with a deformable soft-tip catheter (Angiomedics SOFTIP model), all in the Judkins left 3.5 configuration. The left coronary artery (LCA) was subjected to repeated catheterization; the instruments were also advanced and withdrawn through various segments of the thoracic and abdominal aorta and the right iliac artery. Forty-five arterial tissue sections were collected; these were subjected to histologic analysis 2 weeks after catheterization. When catheterized with the soft-tip instrument, muscular arteries such as the LCA and the right iliac artery had an 86% reduction in subintimal lesions with a disrupted or split internal elastic membrane, compared to muscular arteries catheterized with a conventional instrument (p <.017). Moreover, two medial tears were produced by the conventional catheters. On a scale of 1 to 3 (3 being the most severe), the average severity of muscular arterial lesions observed after use of the soft-tip catheter was 1.0, whereas the average severity associated with conventional catheters was 2.0 (p <.02). No significant differences were observed in elastic (aortic) segments. Therefore, this study showed that subacute, subintimal vascular lesions induced by conventional angiographic catheters are more frequent, more serious, and more likely to penetrate the internal elastic membrane than are lesions produced by soft-tip catheters. Obviously, then, soft-tip catheters offer a safer, less traumatic approach to diagnostic and interventional cardiology.

A less traumatic catheter for coronary arteriography.

A deformable soft-tipped angiographic catheter has been designed and developed to reduce vascular trauma during coronary arteriography. In order to test the ability of the catheter tip glide over vascular endothelium, the coefficient of resistance was tested using fresh human aortic tissue. The mean frictional coefficients of resistance (FRc) for the soft-tipped catheter, as compared with two commonly used catheters (N = 10/group), were .78 +/- .08 units for the soft-tipped catheter and 1.10 +/- .10 (p less than .006) and .98 +/- .10 (p less than .034) for the conventional catheters. This demonstrates a significant 23% reduction in FRc with the soft-tipped catheter. The ease of penetration into a wax media was also measured using the soft-tipped catheter and compared with the same two conventional catheters. The indentation depths for the soft-tipped catheter and the two other catheter groups (N = 7/group) were 140 +/- 18 micron, 246 +/- 15 micron and 318 +/- 20 micron, respectively. This represents a 56% decrease in indentation depth with the soft-tipped catheter. Histologic studies in canines have demonstrated considerably less endothelial damage and subsequent intimal proliferation in the aorta and coronary ostia with the soft-tipped catheters compared with control catheters. It is concluded that a soft-tipped angiographic catheter is less traumatic to vascular tissue and may offer a safer approach to intravascular studies.

Porous electrodes: concept, technology and results.

Porous electrodes were designed and implanted to optimize sensing and pacing performance of the cardiac pacemaker. These electrodes were manufactured to create an effective, atraumatic endocardial interface in order to (1) decrease chronic stimulation thresholds and pacemaker current drain; (2) facilitate fibrous protein tissue ingrowth for reduced electrode displacement; and (3) to create a large electrolytic surface area of contact for reduced polarization voltage, thus improving impulse and electrogram transmission. Thus far, clinical results demonstrate reduced long-term threshold and decreased current drain. Long-term advantages of porous electrodes remain to be determined.

Interactions of blood with solid and porous endocardial electrodes for cardiac pacemakers.

Two forms of implantable endocarial electrodes, solid and porous, used in conjunction with cardiac pacemakers have been compared in their interactions with human blood components. The platinum-iridium electrode tips were suspended in stirred, anticoagulated whole blood or blood products at 37 degrees C for period of 1 to 20 minutes, and then were examined by scanning electron microscopy. The various media employed were heparinized or citrated fresh whole blood, platelet-rich plasma, platelet-poor plasma, and washed platelets in a protein-free balanced salt solution. There were no significant qualitative differences between the reactions of the two forms of electrode. Plasma products, platelets, and erythrocytes adhered freely to the surfaces of both forms of electrode. Leukocytes were much less frequently encountered. Platelets were seen in two forms, those adherent directly to the metal surface with extensive spreading and formation of a monolayer, and platelets attached to the monolayer without spreading but with early shape-change. Quantitative differences between the two electrode forms were prominent. Solid electrodes had broad areas free of cellular accumulations or with only sparsely scattered platelets and erythrocytes. The wires of the porous electrodes were extensively coated on their outer surfaces with platelets and erythrocytes. It is postulated that the porous electrodes will carry appreciably more blood cells, particularly platelets, to the site of endocardial implantation, and these cells or their products may play a role in the tissue responses that result in implantation of the electrode.

Localized nodular synovitis of the knee: a case report.

A 25-year-old man with chronic swelling of the right knee had a mass that was eventually palpated in the suprapatellar pouch. Arthrotomy and biopsy revealed localized nodular synovitis. Since surgical excision of the mass the patient has been asymptomatic. While localized nodular synovitis generally appears as an internal derangement of the joint, this patient had signs and symptoms of chronic monoarthritis.

Physiological and electrical characteristics of the porous endocardial electrode.

The principal complications in pacemaker therapy involve electrode-tissue instability. A new porous electrode has been devised that allows tissue ingrowth into the electrode interior, improving electrode biocompatibility and resulting in reduced dislodgment incidence, lower pacing thresholds, and improved sensing. Electrode porosity reduces polarization impedance permitting small-electrode design for both improved pacing longevity and optimal sensing function.

A new model for the study of septic shock.

Septic shock was produced in 28 healthy mongrel dogs by injecting 10(8) Escherichia coli organisms per kilogram into the gallbladder following division of the cystic artery and duct. Based upon the circulatory responses and the mortality, two distinct groups emerged. In one, the cardiac index decreased significantly, and the total peripheral resistance was elevated. In the other, the cardiac index increased significantly, and the total peripheral resistance was significantly lower. The average survival time in the former group was three days and, in the latter, five days. The physiopathology of this model is remarkably similar to that of human septic shock. Studies are planned to further describe this model to increase its utility in the study of septic shock.

PIP: The need for an experimental model of septic shock which closely approximates the clinical setting led to a series of investigations, and initial results with such a model are reported. Fasting adult mongrel dogs, weighing between 18 and 24 kilograms, were used in the experiments. Septic shock was produced by injecting escherichia coli organisms into the gallbladder following division of the cystic artery and duct. In terms of circulatory response and the mortality, 2 distinct groups emerged. In 1 group the cardiac index increased significantly, and the total peripheral resistance was elevated. In the other group, the cardiac index increased significantly, and the total peripheral resistance was signficiantly lower. The average survival time in the former group was 3 days; it was 5 days in the latter group. The physiopathology of this model is similar to that of human septic shock.

Temporal factors in the reduction of myocardial infarct volume by methylprednisolone.

With a canine model of myocardial infarction [ligation of the left anterior descending (LAD) coronary artery] and an intracellular stain for lactic dehydrogenase (LDH) to directly measure size of infarction, the influence of 30 mg. per kilogram of methylprednisolone sodium succinate was evaluted. The intravenous administration of a pharmacologic dose of methylprednisolone one, 2, or 3 hours after the onset of myocardial infarction significantly reduced the ultimate extent of myocardial necrosis, with the greatest reduction seen following the injection of the drug one hour after ligation. The left atrial pressure was significantly decreased by corticosteroid administration, whereas the cardiac index and peripheral vascular tone were improved insignificantly. Inconsistent and/or insignificant effects were observed in the systemic and coronary sinus blood gases and in those indices of myocardial metabolism which were determined. The potential impact of these findings on the clinical applicability of methylprednisolone sodium succinate in acute myocardial ischemia is discussed.

Effects of allopurinol, propranolol and methylprednisolone on infarct size in experimental myocardial infarction.

With use of a canine model of occlusion of the left anterior descending coronary artery and an intracellular lactic dehydrogenase stain to measure infarct size directly, the effects of allopurinol, methylprednisolone sodium succinate and propranolol were studied. Allopurinol did not influence the extent of myocardial necrosis, whereas both methylprednisolone and propranolol significantly reduced myocardial infarct size. Possible mechanisms of action and clinical applicability of these agents are discussed.

Hemodynamic effects of slow and rapid defibrination with defibrizyme, the thrombin-like enzyme from venom of the timber rattlesnake.

The hemodynamic response to slow and rapid defibrination was sutdied in anesthetized beagle dogs, with the following results: 1. Slow defibrination was a benign procedure that had little or no effect on the hemodynamic variables studied. 2. Rapid defibrination induced statistically significant decreases in cardiac output, stroke volume, and mean aortic arterial pressure. 3. Bradycardia, a drop in mean left v"ntricular pressure, cardiac and minute work indices, an increase in pulmonary artery pressure, and a drastic rise in pulmonary and systemic vascular resistances were also observed. Although physiologically apparent, these changes were not statistically significantly different from control levels. 4. Pulmonary capillary wedge pressure, left ventricular end-disatolic pressure, arterial pH, and blood gases were not altered by rapid defibrination. 5. In view of the similarities between the hemodynamic changes observed after rapid defibrination and acute myocardial ischemia, the role of decreasing fibrinogen concentrations and blood viscosity in aucte myocardial infarction and the sudden death syndrome is questioned.