Comparison of Ventricular Function in Atrial Rate Adaptive Versus Dual Chamber Rate Adaptive Pacing During Exercise

The hemodynamic effects of two different pacing modes—rate adaptive atrial (AAIR) versus dual chamber (DDDR) pacing—were assessed in 12 patients with DDDR pacemakers during upright bicycle exercise first-pass radionuclide angiography using a multiwire gamma camera with tantalum-178 as a tracer. All patients had sinus node disease with intact AV conduction. Patients exercised to the same heart rate in random order in these two different pacing modes, AAIR and DDDR with AV delay (of 100 msec) selected to maintain 100% ventricular capture. Cardiac output in creased significantly above baseline values during exercise in both pacing modes: 154 ± 41% (mean ± SEM, P = 0.002) with AAIR, versus 95 ± 24% (P = 0.004) with DDDR (P = NS between the two modes). The peak filling rate, likewise, increased in both pacing modes (2.3 ± 0.21 end-diastolic volumes/sec to 3.8 ± 0.31 end-diastolic volumes/sec in AAIR [P = 0.0004] and 2.2 ± 0.18 end-diastolic volumes/sec to 3.4 ± 0.27 end-diastolic volumes/sec in DDDR [P = 0.0008]). LV ejection fraction was normal at rest (60 ± 4%, SEM) and did not significantly change with submaximal exercise in either pacing mode (both 56%, P = NS). No significant changes in end-diastolic volume or stroke volume indexes occurred with exercise in either pacing mode. Our study demonstrates that in patients with normal resting LV function, AAIR and DDDR pacing are equally effective in attaining appropriate increases in cardiac output and LV filling during exercise.     

Radiofrequency Catheter Ablation of the Slow Reentrant Pathway of Sustained Ventricular Tachycardia

The article reports the cases of two patients with severe coronary artery disease and associated recurrent sustained ventricular tachycardia successfully treated with radiofrequency catheter ablation. In the first patient, two different types of ventricular tachycardia (one incessant) were eliminated. In all procedures, an area of slow conduction critical for tachycardia maintenance was localized by endocardial mapping techniques. Radiofrequency energy delivered to this area could permanently modify the anatomical substrate of the arrhythmia. After single follow-ups of 19, 14, and 13 months regarding the arrhythmic entities, the patients are well and free from spontaneous recurrences.     

Characterization of Conduction in the Ventricles of Normal and Heterozygous Cx43 Knockout Mice Using Optical Mapping

INTRODUCTION: Gap junction channels are important determinants of conduction in the heart and may play a central role in the development of lethal cardiac arrhythmias. The recent development of a Cx43-deficient mouse has raised fundamental questions about the role of specific connexin isoforms in intercellular communication in the heart. Although a homozygous null mutation of the Cx43 gene (Cx43-/-) is lethal, the heterozygous (Cx43+/-) animals survive to adulthood. Reports on the cardiac electrophysiologic phenotype of the Cx43+/- mice are contradictory. Thus, the effects of a null mutation of a single Cx43 allele require reevaluation. METHODS AND RESULTS: High-resolution video mapping techniques were used to study propagation in hearts from Cx43+/- and littermate control (Cx43+/+) mice. Local conduction velocities (CVs) and conduction patterns were quantitatively measured by determining conduction vectors. We undertook the characterization of ECG parameters and epicardial CVs of normal and Cx43+/- mouse hearts. ECG measurements obtained from 12 Cx43+/+ and 6 Cx43+/- age matched mice did not show differences in any parameter, including QRS duration (14.5 +/- 0.9 and 15.7 +/- 2.3 msec for Cx43+/+ and Cx43+/-, respectively). In addition, using a sensitive method of detecting changes in local CV, video images of epicardial wave propagation revealed similar activation patterns and velocities in both groups of mice. CONCLUSION: A sensitive method that accurately measures local CVs throughout the ventricles revealed no changes in Cx43+/- mice, which is consistent with the demonstration that ECG parameter values in the heterozygous mice are the same as those in wild-type mice.     

Mycotic Aneurysm of the Aortic Arch with Aortoesophageal Fistula

An elderly man presented with an aortoesophageal fistula (AEF) and underwent resection of a mycotic aneurysm of the aortic arch. After an initial success, the patient ultimately succumbed to mediastinal sepsis. The various approaches to combined aortic and esophageal pathology are presented with the recommendation for aortic replacement along with early removal of mediastinal contamination.     

Laser Scanner Observations of Heterogeneous Conduction Patterns in Rabbit Epicardium Induced by Cellular Uncoupling with Heptanol

Heptanol Disrupts Epicardial Conduction. This study examines how severely reduced intercellular electrical coupling affects the pattern of activation of left ventricular rahhit epicardium. Five thin (< 1-mm thick) flaps of < 60 mm² were stained in vitro with potentiometric dye WW781. A helium-neon laser beam was scanned over 63 spots on each flap, and the voltage-dependent fluorescence intensity from each spot was used to construct maps of the activation resulting from pacing at a single site. Introducing heptanol (1.75 mM) produced lines of conduction hlock in four of the five preparations after times ranging from 7 to 71 minutes; at varying intervals during this time, activation patterns were obtained. Fiber orientation was later determined from histologic sections. Heptanol changed the relatively uniform conduction seen under control conditions to heterogeneous patterns having regions of slowed conduction and lines of partial and complete block oriented predominantly parallel to the fiber direction (i.e., transverse propagation was blocked). The two partial blocks, which did not extend across the entire tissue, caused the activation wave to pivot around one end of the block line. The subsequent retrograde activation of the line's distal side was consequently delayed. Two points on opposite sides of these hlocks, separated by < 1 mm, had activation times differing by as much as 89 msec rather than a normal 3–5 msec. Thus, sufficient uncoupling can alter conduction pathways on the scale of a few millimeters. The resulting dispersion in activation times at closely spaced points may predispose poorly-coupled cardiac tissue to development of reentrant arrhythmias. (J Cardiovasc Electrophysiol. Voi. I, pp, 426–436. October 1990)     

Selective β1-Andrenoceptor Blockade and Muscle Thermogenesis

ABSTRACT Muscle thermogenesis was measured by direct microcalorimetry in hypertensive patients randomly treated with either metoprolol or placebo. Samples from rectus abdominis were taken after muscle relaxation during surgery, which was accompanied by a significant increase in arterial plasma noradrenaline. Thermogenesis was significantly lower in the metoprolol group compared with both the hypertensives given (p < 0.05), and a normotensive group without treatment (p < 0.005). Metoprolol also provoked a significant fall in body temperature in comparison with the two other groups (p < 0.01). In the hypertensives given placebo, heat production was inversely related to plasma adrenaline (r = -0.89), indicating a role of the sympatho-adrenal system in muscle thermogenesis. No such correlation appeared during metoprolol treatment. In the present acute stress situation it is suggested that muscle thermogenesis was decreased indirectly by metoprolol via blockade of β₁-receptors in adipose tissue, causing a relative inhibition of lipolysis with diminished substrate supply to the muscles.     

QUANTIFYING RISK OF PENILE PROSTHESIS INFECTION WITH ELEVATED GLYCOSYLATED HEMOGLOBIN

Purpose

Elevation of glycosylated hemoglobin above levels of 11.5 mg.% has been considered a contraindication to penile prosthesis implantation in diabetic patients. We determine the predictive value of glycosylated hemoglobin A1C in penile prosthesis infections in diabetic and nondiabetic patients to confirm or deny this prevalent opinion.

Materials and Methods

We conducted a 2-year prospective study of 389 patients, including 114 diabetics, who underwent 3-piece penile prosthesis implantation. All patients had similar preoperative preparation without regard to diabetic status, control or glycosylated hemoglobin A1C level. Risk of infection was statistically analyzed for diabetics versus nondiabetics, glycosylated hemoglobin A1C values above and below 11.5 mg.%, insulin dependent versus oral medication diabetics, and fasting blood sugars above and below 180 mg.%.

Results

Prosthesis infections developed in 10 diabetics (8.7%) and 11 nondiabetics (4.0%). No increased infection rate was observed in diabetics with high fasting sugars or diabetics on insulin. There was no statistically significant increased infection risk with increased levels of glycosylated hemoglobin A1C among all patients or among only the diabetics. In fact, there was no meaningful difference in the median or mean level of glycosylated hemoglobin A1C in the infected and noninfected patients regardless of diabetes.

Conclusions

Use of glycosylated hemoglobin A1C values to identify and exclude surgical candidates with increased risk of infections is not proved by this study. Elevation of fasting sugar or insulin dependence also does not increase risk of infection in diabetics undergoing prosthesis implantation.     

Growth Factors: Thrombopoietic Property of the Pineal Hormone Melatonin

The recent advances in the psychoneuroimmunology have suggested that the hematopoiesis may be under a neuroendocrine regulation, mainly exerted by the pineal gland. In particular, melatonin (MLT), which is the main pineal hormone, has appeared to stimulate platelet generation, probably by promoting the megakaryocyte fragmentation and modulating the cytokine network involved in platelet production. On this basis, we have evaluated the effect of pharmacological doses of MLT on platelet number in patients with persistent thrombocytopenia due to different causes. The study included 200 patients, who were randomized to receive supportive care alone or MLT at 20 mg/day orally in the evening, for al least 1 month. No MLT-related toxicity occured. Platelet mean number rapidly and significantly increased in response to MLT, and a normalization of platelet number was achieved on MLT therapy in 71/98 (72%) patients. The least responsive form of thrombocytopenia was DIC. This study shows that the pineal hormone MLT may represent a well tolerable and effective therapy of thrombocytopenia due to different pathogenetic mechanisms.