Multiple spin-echo magnetic resonance imaging

Spin-echo magnetic resonance (MR) imaging detects a variety of pathologic states with great sensitivity. A technique for producing multiple spin-echo images in multisection operation is presented. This method of intensity-image acquisition is compared with retrospective intensity-image synthesis from routine data sets. Both yield long echo time (TE) images with similar image contrast and comparable and often increased diagnostic utility. Technical and clinical considerations are addressed, including signal-to-noise levels, flow effects, and patient throughput.     

Spinal cord stimulation: a new method to produce an effective cough in patients with spinal cord injury

Patients with spinal cord injury have an increased risk of developing respiratory tract infections as the result of expiratory muscle paralysis and consequent inability to cough. We have developed a method by which the expiratory muscles can be activated via lower thoracic and upper lumbar spinal cord stimulation to produce an effective cough mechanism. In a tetraplegic patient who required frequent (8.57+/-2.3 times per week [mean+/-SEM]) caregiver assistance to facilitate airway clearance and expectoration of secretions, three epidural electrodes were applied in the T9, T11, and L1 spinal cord regions. During stimulation at the T9 and L1 levels, airway pressures were 90 and 82 cm H2O, respectively. Peak expiratory flow rates were 6.4 L/s and 5.0 L/s; respectively. During combined (T9+L1) stimulation, airway pressure and expiratory flow rate increased to 132 cm H2O and 7.4 L/s, respectively. Addition of the third lead did not result in further increases in pressure generation. These values are characteristic of those observed with a normal subject. Because the patient is able to trigger the device independently, he no longer requires caregiver support for airway management. If confirmed in additional patients, spinal cord stimulation may be a useful method to restore an effective cough mechanism in patients with spinal cord injury.     

Hypergammaglobulinemia can be associated with a positive direct antiglobulin test, a nonreactive eluate, and no evidence of hemolysis

To determine the cause of a positive direct antiglobulin test (DAT), blood banks routinely perform serologic tests on eluates prepared from DAT-positive red cells. Negative eluates traditionally have been suspected to be associated with drug reactions. This report confirms that the most frequent cause of a positive DAT and a nonreactive eluate is hypergammaglobulinemia. The results of 74 patient samples with positive DATs were analyzed retrospectively. Eluates prepared from the red cells of 54 patients (72.9%) reacted; eluates from 20 patients (27.1%) did not react. This latter group had identical serologic and clinical findings, suggesting that they made up a homogeneous group. In particular, the patients had a positive DAT, a negative indirect antiglobulin test, and a negative eluate; an increased serum concentration of IgG; and no evidence of hemolysis. In a subsequent study, DATs were performed prospectively on red cells from 44 consecutive patients with elevated serum IgG levels. The serum IgG concentration was highest in the three patients whose red cells had a positive DAT. The DAT also became positive in two patients treated with high-dose intravenous gammaglobulin (IV IgG). These studies indicate that a negative eluate from red cells with a positive DAT, a common serologic finding, is often caused by hypergammaglobulinemia. The authors postulate that IgG binds nonspecifically to the red cells because of the hypergammaglobulinemia.     

Electrocardiographic abnormalities after radiofrequency catheter ablation of accessory bypass tracts in the Wolff-Parkinson-White syndrome.

Repolarization abnormalities on surface electrocardiograms have been described after loss of ventricular preexcitation in some patients with the Wolff-Parkinson-White syndrome. Radiofrequency catheter ablation of overt accessory pathways provides a unique opportunity to study this phenomenon. In this study, serial electrocardiograms were obtained before and after radiofrequency ablation of manifest accessory pathways in 19 patients, of concealed accessory pathways in 6 and after radiofrequency atrioventricular nodal modification in 12. Seven patients undergoing manifest right-sided accessory pathway ablation had left superior frontal plane T-wave axis deviations after ablation (-42 +/- 13 degrees). No patient with a manifest left-sided or concealed accessory pathway, or atrioventricular nodal modification had T-wave abnormalities after ablation; however, left anterior fascicular block and incomplete right bundle branch block each occurred in 1 patient with left accessory pathway ablation. Repolarization abnormalities observed after ablation were similar to T-wave abnormalities during the absence of preexcitation before ablation and persisted up to 5 weeks after the procedure. Patients with repolarization abnormalities after ablation had significantly longer preexcited QRS durations than those without such changes, suggesting that the initial contribution of the pathway to ventricular activation is an important determinant of T-wave changes after ablation. The proposed mechanism for repolarization abnormalities after ablation is the phenomenon of T-wave "memory."     

Surgical ablation of ventricular tachycardia with sequential map-guided subendocardial resection: electrophysiologic assessment and long-term follow-up

A new operative technique of sequential map-guided subendocardial resection (SER) was used in 45 consecutive patients for the treatment of sustained ventricular tachycardia due to coronary artery disease. This technique is characterized by map-guided SER or cryothermic ablation during normothermic cardiopulmonary bypass, followed by repeated sequences of programmed stimulation to assess adequacy of resection. The patients' mean age was 59 +/- 10 years and the mean left ventricular ejection fraction was 34 +/- 12%. Twenty-five (56%) patients had a history of myocardial infarction within the previous 2 months. After ventriculotomy, 34 patients (76%) had inducible monomorphic ventricular tachycardia. These patients underwent repeated sequences of ventricular tachycardia induction and mapping during normothermic bypass followed by successive SER or cryothermic ablation until sustained monomorphic ventricular tachycardia was no longer inducible. Twenty-seven patients had a total of 60 discrete, mappable tachycardias induced and seven patients had 10 discrete tachycardias that were too fast to accurately map. In the remaining 11 patients, no ventricular tachycardia was inducible after ventriculotomy and SER, which included all visually identifiable scar, was performed. The mean cardiopulmonary bypass time was 102 +/- 27 min. Forty-one of 45 patients (91%) survived to hospital discharge, and 35 of 41 patients (85%) had no inducible ventricular tachycardia at postoperative electrophysiologic evaluation performed in the absence of all antiarrhythmic drugs. The remaining six patients had no inducible ventricular tachycardia with drug therapy. All four operative nonsurvivors had refractory cardiac collapse preoperatively. Over 19 +/- 12 months of follow-up, there were four sudden cardiac deaths and no nonfatal recurrences of ventricular tachycardia. There were seven additional cardiac deaths. Actuarial cardiac survival was 0.57, and freedom from arrhythmic events was 0.76 at 42 months. Thus, in the absence of cardiogenic shock, the technique of sequential map-guided SER achieves: (1) a high operative survival with acceptable perfusion times, (2) excellent long-term arrhythmia control, and (3) survival comparable to that in patients with similar left ventricular function and no history of ventricular tachyarrhythmia.     

Functional magnetic stimulation of the respiratory muscles in dogs

This study assessed the ability of functional magnetic stimulation (FMS) to activate the respiratory muscles in dogs. With the animal supine, FMS of the phrenic nerves using a high-speed magnetic stimulator was performed by placing a round magnetic coil (MC) at the carotid triangle. Following hyperventilation-induced apnea, changes in volume (ΔV) and airway pressure (ΔP) against an occluded airway were determined. FMS of the phrenic nerves produced substantial inspired function (ΔV = 373 ± 20.5 mL and ΔP = −20 ± 2.0 cm H₂O). After bilateral phrenectomies, maximal inspired ΔV (219 ± 12.2 mL) and ΔP (−10 ± 1.0 cm H₂O) were produced when the MC was placed near the C6–C7 spinous processes, while maximal expired ΔV (−199 ± 22.5 mL) and ΔP (11 ± 2.3 cm H₂O) were produced following stimulation near the T9–T10 spinous processes. We conclude: (1) FMS of either the phrenic or upper intercostal nerves results in inspired volume production; (2) FMS of the lower intercostal nerves generates expired volume production; and (3) FMS of the respiratory muscles may be a useful noninvasive tool for artificial ventilation and assisted cough in patients with spinal cord injuries or other neurological disorders. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:1048–1057, 1998.     

Does a posterior aneurysm increase the risk of endocardial resection?

The bias has been that the ideal anatomic circumstance for endocardial resection is the anterior left ventricular location. Posterior left ventricular aneurysms have been thought to be problematic to map and more difficult to close, and possibly to have a different substrate for ventricular tachycardia. To address this problem, we retrospectively reviewed the cases of 110 consecutive patients who underwent sequential endocardial resection for ventricular tachycardia between 1983 and 1991. Ninety-six patients had an anterior aneurysm, and 14 patients had a posterior aneurysm or infarct. Operative survival and 5-year survival were very similar between the two groups (p = not significant). A positive postoperative electrophysiological study was present in 11% of the anterior group versus 14% of the posterior group (p = not significant). There was a significantly greater incidence of mitral valve replacement in the posterior group, and we believe this was most likely due to frequent localization of the arrhythmia to the papillary muscle. Otherwise, patients with a posterior aneurysm or infarct had surgical results equivalent to those in patients with an anterior location. As long as there is a discrete aneurysm or infarct, endocardial resection is a safe and effective therapeutic procedure for ventricular tachycardia.     

Quinidine for ventricular arrhythmias: value of electrophysiologic testing

Quinidine was evaluated during serial electrophysiologic testing with programmed ventricular stimulation in 89 patients with life-threatening ventricular arrhythmias. In 30 of the 89 patients, quinidine therapy prevented the initiation of ventricular tachycardia (VT) during programmed ventricular stimulation. In 8 additional patients no single drug tested was effective, and quinidine in combination with either mexiletine (7 patients) or propranolol (1 patient) prevented the initiation of VT during electrophysiologic testing. The mean serum concentrations of quinidine in the patients who responded and those who failed to respond were 2.9 +/- 0.8 and 2.8 +/- 1.1 micrograms/ml, respectively; however, but nonresponders were characterized by more severe congestive heart failure and an increased incidence of digitalis use. During chronic therapy (24 +/- 3 months) with quinidine either alone or in combination with a second antiarrhythmic drug in the 38 patients whose arrhythmia had been suppressed during electrophysiologic testing, 32 (84%) remain symptom-free while 3 have had recurrent arrhythmia and 3 discontinued quinidine because of adverse effects. These data demonstrate that quinidine, when selected on the basis of electrophysiologic testing, provides effective long-term prophylaxis against recurrent ventricular arrhythmia and that approximately 40% of patients tested are likely to respond either to quinidine alone or quinidine in combination with another antiarrhythmic agent.