Alterations in transmural blood flow and body surface ST segment abnormalities produced by ischemia in the circumflex and left anterior descending coronary arterial beds of the dog

Previous studies have documented a quantitative relation between alterations in transmural myocardial blood flow and body surface electrocardiographic distributions during rapid atrial pacing after chronic occlusion of the left circumflex coronary artery (LCx). Because other studies have described functional differences between the left anterior descending (LAD) and the LCx perfusion beds, we tested the hypothesis that these two territories exhibit quantitative differences in their responses to demand-dependent myocardial ischemia. To do so, 25 sedated dogs were studied 3 weeks after implantation of an ameroid constrictor around the proximal LCx (15 dogs, group I) or the LAD (group II). Oxygen demand was increased by rapid atrial pacing at rates of 90 to 210 beats/min, myocardial blood flow was measured by serial injections of radiolabeled microspheres, and the electrocardiographic consequences were evaluated by isopotential body surface mapping. Endocardial flows and the endocardial/epicardial flow ratio fell to significantly lower levels during atrial pacing in the ischemic LAD bed than in the LCx perfusion zone. Electrocardiographic patterns indicative of subendocardial ischemia also developed with lesser abnormalities in endocardial/epicardial ratios as determined by logistic regression models, in the LAD than in the LCx bed. Thus the LAD bed is more susceptible to ischemia than the LCx region because of differences in collateral blood flow patterns. In addition, the intensity of the surface electrocardiographic potentials during ischemia was significantly greater, as measured by linear regression, after LAD than after LCx obstruction. These data thus demonstrate significant differences between the two cardiac regions as electrocardiographic potential sources during ischemia.     

Posttraumatic cerebral infarction diagnosed by CT: prevalence, origin, and outcome

Posttraumatic cerebral infarction is a recognized complication of craniocerebral trauma, but its frequency, cause, and influence on mortality are not well defined. To ascertain this information, all cranial CT studies demonstrating posttraumatic cerebral infarction and performed during a 40-month period at our trauma center were reviewed. Posttraumatic cerebral infarction was diagnosed by CT within 24 hr of admission (10 patients) and up to 14 days after admission (mean, 3 days) in 25 (1.9%) of 1332 patients who required cranial CT for trauma during the period. Infarcts, in well-defined arterial distributions, were diagnosed either uni- or bilaterally in the posterior cerebral (17), proximal and/or distal anterior cerebral (11), middle cerebral (11), lenticulostriate/thalamoperforating (nine), anterior choroidal (three), and/or vertebrobasilar (two) territories in 23 patients. Two other patients displayed atypical infarction patterns with sharply marginated cortical and subcortical low densities crossing typical vascular territories. CT findings suggested direct vascular compression due to mass effects from edema, contusion, and intra- or extraaxial hematoma as the cause of infarction in 24 patients; there was postmortem verification in five. In one patient, a skull-base fracture crossing the precavernous carotid canal led to occlusion of the internal carotid artery and ipsilateral cerebral infarction. Mortality in craniocerebral trauma with complicating posttraumatic cerebral infarction, 68% in this series, did not differ significantly from that in craniocerebral trauma patients without posttraumatic cerebral infarction when matched for admission Glasgow Coma Score results. Thus, aggressive management should be considered even in the presence of posttraumatic cerebral infarction.     

Intraoperative sonography of cervical spinal cord injury: results in 30 patients

Intraoperative spinal sonography (IOSS) with a 7.5-MHz sector transducer was performed in 30 patients with cervical spine injury associated with neurologic deficits. A laminectomy (25 patients) or anterior corpectomy (five patients) during spinal surgery provided the IOSS imaging window. The surgery was performed for either spinal decompression or fixation as part of the initial care of these patients and occurred 1 to 39 days (mean, 12.4 days) after injury. Parenchymal spinal cord lesions at the level of cervical fracture or stenosis that were compatible with the initial neurologic deficits were detected by IOSS in 28 (96.5%) of 29 patients with technically adequate studies. Lesions appeared as foci of increased echogenicity and were sorted into five injury grades (0 through IV). The IOSS injury grade in each patient was determined by the maximal diameter of regions of increased echogenicity and/or cyst formation in either the sagittal or transverse image plane. The extent of initial neurologic injury and its recovery was assessed by using the ASIA motor score (0 to 100 unit scale) at admission and during follow-up. The IOSS injury grade was correlated with the initial ASIA motor score (p less than 0.009, Spearman's Rank Order Test), indicating that the IOSS echogenicity is related to the extent of initial clinical motor deficit. Regression analysis disclosed that both the IOSS injury grade and the initial ASIA score were correlated with the follow-up ASIA score (p less than 0.05 and p less than 0.001, respectively). However, the addition of the IOSS injury grade to the initial ASIA motor score did not improve the predictive ability of the follow-up ASIA motor score.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fractures of the clivus: classification and clinical features

Fractures of the clival complex were diagnosed in a series of 17 patients admitted to the Maryland Institute for Emergency Medical Services System and the University of Maryland Medical System over a 30-month period. These fractures were divided pathologically into three types based upon their appearance on computed tomography: longitudinal, transverse, and oblique. The mechanisms of injury were similar in all groups, and the Glasgow Coma Scale scores at admission were comparable, regardless of fracture type, in survivors and nonsurvivors. Longitudinal fractures were associated with severe injury to the central nervous system and with brain stem infarction, and 4 of 6 (67%) of these patients died. Transverse fractures of the clival complex were found in 6 patients, 3 of whom (50%) died. All of these patients had fractures of the petrous ridge; 2 of the 3 survivors had multiple cranial nerve deficits, and one patient developed a carotid-cavernous fistula. Of the 5 patients with oblique clival fractures, 2 survived (40%), both of whom had multiple cranial nerve palsies; in addition, one of these patients developed a carotid-cavernous fistula. Using the present generation of computed tomographic scanners, fractures of the clival complex can be reliably diagnosed; they are probably more common than previously believed and can be separated into three groups based on the characteristics on computed tomographic scans and clinical findings.     

The cumulative effects of historical and physical examination findings on the prognostic value of the electrocardiogram.

The electrocardiogram has been shown in epidemiologic studies to be an independent predictor of survival. These studies have adjusted for selected covariates simultaneously. This article assesses the value of the electrocardiogram as a predictor of survival when introduced at progressive stages of the common clinical encounter. Data collected from 4,518 patients ages of 60 to 96 years with isolated systolic hypertension who were followed-up for up to 6 years as part of the Systolic Hypertension in the Elderly Project were analyzed. Survival curves and 3- and 5-year survival rates (Cox regression methods) of groups with normal and abnormal resting electrocardiograms were compared. Blocks of covariates representing demographic information, risk factors for cardiovascular disease, clinical history, and physical examination findings were added to the survival models sequentially to mimic the sequence of the common clinical encounter, and the independent significance of the electrocardiogram as a predictor of survival was assessed at each step. An abnormal electrocardiogram was associated with reduced survival when no adjustment for covariates is made. Survival was also significantly (P <.05) different for groups with normal and abnormal electrocardiograms when demographic and risk factor variables were included in the statistical models, but not after findings from the clinical history and physical examination were added. The prognostic value of the electrocardiogram varies with the stage in the clinical encounter in which it is introduced.     

Determination of the spatial and intensity properties of atrial repolarization potentials in the dog

Body surface electrical potentials generated by atrial repolarization (Ta wave) normally extend from the P wave into or through the QRS complex. Thus, the Ta wave is partially obscured by the QRS complex and, conversely, the QRS complex is composed of atrial recovery as well as ventricular depolarization forces. To better study the spatial patterns and magnitudes of the Ta wave, transient atrioventricular (AV) block was induced in 15 dogs by atrial pacing using surgically implanted left or right atrial electrodes. ECG potentials were registered from 84 torso electrodes, and cycles with normal and with blocked AV conduction were segregated. In blocked cycles, the duration of the Ta wave measured 248.0 +/- 25.3 msec with right and 256.0 +/- 38.4 msec with left atrial stimulation. In all cases, the Ta wave extended into the QRS and, in 75% of cases, it extended into the S-T segment. Peak Ta magnitudes, measuring 50.7 +/- 17.9 and 51.8 +/- 21.7 uV RMS with right and left atrial stimulation, respectively, occurred during the P-R segment in all cases. The effect of Ta wave superposition on the QRS complex was assessed by subtraction of patterns in cycles with blocked AV conduction from those with intact AV conduction. Differences between directly recorded QRS waveforms and those computed by subtraction of the Ta wave were small; correlation coefficients exceeded 0.96 and differences in instantaneous RMS potential were less than 6%. Thus, the atrial recovery waveform does extend into the QRS and into the S-T segment in most cases, but the effect of this superposition of Ta on QRS waveforms is quantitatively small.     

A system oriented electrocardiographic amplifier.

A low noise, programmable gain amplifier has been developed for acquiring ECG data from a variety of recording environments. Features include: low noise (4muV peak-to-peak) differential inputs; digitally programmable gains (range 100 to 16000) and output DC offsets (range -3.5 to +4 V) controlled via a serial interface; externally selectable low frequency response (0.04 or 0.08 Hz); and an on-board output monitor multiplexer controlled via a second serial interface.     

Evaluation of normal variations in S-T segment patterns by body surface isopotential mapping: S-T segment elevation in absence of heart disease

S-T segment elevation is commonly observed in the electrocardiogram of normal persons. To study the possible origins of such patterns, 45 normal volunteers were examined. Electrocardiographic potentials were registered from 150 torso electrodes and processed to construct iso-potential maps at 2 ms intervals throughout the QRS-T interval. The maximal potentials recorded from any of the 150 electrodes were 198 ± 76.4 and 272.1 ± 84.2 μV at instants 40 and 80 ms into the S-T segment, respectively. Maximal voltages recorded by the six standard precordial V leads at these respective time points were 109.7 ± 57.0 and 163.6 ±66.9 μV. Torso maximal potentials were significantly stronger than were those sensed by V leads; the two were significantly correlated but predictability was limited. The duration of overlap between the onset of ventricular recovery and the end of the excitation was determined from isopotential maps and ranged from 4 to 16 ms. There was no significant correlation (p > 0.05) between these values and either torso or V lead potentials at either 40 or 80 ms into S-T segment.These data suggest that (1) standard precordial leads do not accurately predict maximal torso potentials during the S-T segment, and (2) the degree of overlap between repolarization and depolarization is not a major determinant of precordial voltage. Hence, the rationale for use of the term “early repolarization” to describe this clinical condition is not substantiated.     

Traumatic avulsion of the ureter: computed tomography correlation

Avulsion of the ureter is a rare but significant traumatic injury, and there is often a delay in diagnosis and treatment. Radiologic signs have been described for intravenous urography but are not always present. To our knowledge, the computed tomographic appearance of avulsion of the ureter has not been described. Herein, we report the contrast-enhanced computed tomography findings in a case of traumatic avulsion of the ureter.