Biomedical subjects

Charles Kennergren

Publications and source records attributed to Charles Kennergren.

6 recordsLinked to original sources

PubMed2005

Clinical performance of a ventricular automatic capture verification algorithm.

BACKGROUND: This study was conducted to evaluate the clinical performance of the ventricular automatic capture feature as implemented in the Insignia I Ultra pacemaker system (Guidant) utilizing a variety of ventricular leads. Currently, the optimal programming of the pacemaker output considers both pacemaker efficiency (prolonging battery longevity) and patient safety (adequate safety margin). The ability of a pacemaker to automatically adjust the ventricular output above the pacing threshold while maintaining the appropriate safety margin has been explored since the early 1970s and is only available today in conjunction with a specific low polarization lead system. METHODS: One hundred and five patients were enrolled from 17 European centers utilizing 31 different types of ventricular leads were followed through their 3-month follow-up visit. There were no restrictions on the type of ventricular leads used. RESULTS: The average mean difference between the commanded autothreshold test (0.652 + 0.335 V) and the manual threshold test (0.651 + 0.335 V) was 0.001 + 0.49 (P < 0.0001). The average mean difference between the ambulatory autothreshold test (0.696 + 0.322 V) and the commanded autothreshold test (0.682 + 0.315 V) was 0.002 + 0.74 (P < 0.0001). Holter recordings confirmed that there were no loss of capture incidences without a backup pulse being delivered. In addition, the mean number of backup pulses delivered in a 24-hour period was less than 0.1% of the total number of paced beats. CONCLUSIONS: This study provided that the automatic capture feature while using a variety of leads accurately determines the ventricular stimulation threshold and safely delivers a backup pulse when required.

Adult↗

PubMed2004

Pacemaker endocarditis during 18 years in Göteborg.

Pacemaker endocarditis is a rare but serious complication. Few studies addressing its treatment have been published. Clinical characteristics and outcome were retrospectively studied in 38 patients with 44 episodes of pacemaker infective endocarditis (PMIE) in Göteborg, during 1984-2001. The male/female ratio of episodes was 27/17 and the mean age 69 y. Transthoracic echocardiography (TTE) showed vegetation in 4/22 (18%) episodes and transoesophageal echocardiography (TEE) in 22/33 (67%). Staphylococci were isolated in 66% of blood cultures. The pacemaker system (PS) was removed in 28 episodes and in 18 of these there were no signs of reinfection at follow-up. In 16 episodes the PS was not removed, and in 13 of these, signs of infection were found at follow-up. Thus, the present study of PMIE showed staphylococci to be predominant causative agents and demonstrated a high diagnostic sensitivity of TEE. According to our results, PM removal rather than conservative treatment should be considered in all cases.

Adult↗

PubMed2003

Clinical experience with an automatic threshold tracking algorithm study.

The automatic threshold tracking pacing system algorithm developed by St. Jude Medical, verifies ventricular capture beat by beat by recognizing the evoked response (ER) following each pacemaker stimulus. The present automatic threshold tracking function requires a bipolar ventricular lead with low polarization. The aim of this study was to evaluate a new algorithm developed to use with unipolar leads with different levels of polarization. An external pacemaker with the ability to sense intrinsic R waves and measure ER signals, as well as deliver stimulus, was used. An algorithm for detecting the true ER in a unipolar sensing configuration (tip-case) was developed. Based on the assumption that the true evoked R wave amplitude is independent of the stimulation amplitude, the algorithm calculates and subtracts the polarization present at any pacing stimulus from the measured ER. The resulting signal is analyzed to verify capture. This study comprises 35 patients of which 26 were new implants and 9 had chronic leads. The automatic threshold-tracking algorithm was calibrated for each patient and pacing was performed at different pulse amplitudes and pulse duration. Capture was verified for each paced beat. The recordings were stored for later comparison with the tape-recorded intracardiac heart signals. The new algorithm correctly verified capture or loss of capture for every single analyzed beat at the different pacing outputs in every individual patient. The results from this initial study suggests that the new ER detection principle will allow automatic threshold tracking to be used not only with low polarization bipolar leads but with most leads.

Aged↗

PubMed2002

Myocardial interstitial glucose and lactate before, during, and after cardioplegic heart arrest.

The interstitial fluid of the human myocardium was monitored in 13 patients undergoing aortic valve and/or bypass surgery before, during, and after hypothermic potassium cardioplegia. The regulation of glucose and lactate was studied after sampling with microdialysis. The following questions were addressed. 1). Is the rate of transcapillary diffusion the limiting step for myocardial uptake of glucose before or after cardioplegia? 2). Does cold potassium cardioplegia induce a critical deprivation of glucose and/or accumulation of lactate in the myocardium? Before cardioplegia, interstitial glucose was approximately 50% of the plasma level (P < 0.001). Interstitial glucose decreased significantly immediately after induction of cardioplegia and remained low (1.25 +/- 0.25 mM) throughout cardioplegia. It was restored to precardioplegic levels 1 h after release of the aortic clamp. Interstitial glucose then decreased again at 25 and 35 h postoperatively to the levels observed during cardioplegia. Interstitial lactate decreased immediately after induction of cardioplegia but returned to basal level during the clamping period. At 25 and 35 h, interstitial lactate was significantly lower than before and during cardioplegia. Glucose transport over the capillary endothelium is considered rate limiting for its uptake in the working heart but not during cold potassium cardioplegia despite the glucose deprivation following perfusion of glucose-free cardioplegic solution. Lactate accumulated during cardioplegia but never reached exceedingly high interstitial levels. We conclude that microdialysis provides information that may be relevant for myocardial protection during open-heart surgery.

Adult↗

PubMed2002

Morphologic and immunohistochemical observations of tissues surrounding retrieved transvenous pacemaker leads.

Immunohistochemical and morphologic techniques were employed to evaluate the tissue response around chronically implanted pacing leads. Seventeen leads were retrieved from 12 patients. Leads were extracted by direct manual traction (1), extraction with sheaths and locking stylets (1), or with by a combination of mechanical tools and Excimer laser sheaths (15). Mean lead implantation time was 5.6 years (range 1-8 years). Frozen sections, 6-8 microm thick, were incubated with antibodies against HLA-DR antigen, endothelial cells, macrophages, T cells, plasma cells, fibrinogen, and interleukin-1beta. Prominent morphologic observations were fibrous encapsulations of the leads. Immunohistochemical analysis revealed a tissue generally devoid of inflammatory and immune cells. The fibrous capsule surrounding the lead was partially or completely covered with a monolayer of CD34 expressing endothelial cells. The results from this study provide useful information in design and material selection for pacemaker leads. Endothelialization of the fibrous encapsulation indicates a functionalization of blood-contacting surfaces around pacemaker materials, thus providing a mechanism for long-term persistence of foreign materials in the blood. The laser method allowed an efficient extraction of pacemaker leads without damage to the studied tissues, as suggested by the presence of immunolabeled cells close to the cut surfaces.

Adult↗

PubMed2002

Intramyocardial troponin-T monitoring with microdialysis in coronary artery bypass surgery.

OBJECTIVE: To investigate the time course of troponin-T release into the extracellular fluid of the myocardium and to distinguish between a rise in troponin-T due to implantation trauma and an increase due to cardiac arrest during coronary surgery. DESIGN: Microdialysis probes were implanted in the heart of seven patients soon after sternotomy. Troponin-T was measured in the microdialysates and in peripheral blood from 3 h before to 24 h after heart arrest. RESULTS: The troponin-T concentration in the microdialysates increased immediately after probe implantation and decreased to baseline within 70 min. This early peak is interpreted to reflect a local trauma. Three hours after cross-clamp release, a second peak of microdialysate troponin-T was recorded; 50 times higher than in serum. Eight to 24 h later a third peak occurred in five patients. Serum troponin-T was below the detection level at the beginning of the operation but increased linearly during the first 3 h of reperfusion and remained at that level thereafter. CONCLUSION: Microdialysis is a safe technique providing more information on myocardial metabolism during and after bypass surgery than can be obtained from peripheral blood. The release of troponin-T in response to cardiac arrest can be distinguished in time from the local tissue response to probe implantation.

Adult↗