Magnetic resonance (MR) images of a variety of cardiac malformations in 19 patients aged 1 week to 33 years were obtained using pulse plethysmographic- or ECG-gated spin echo pulse sequences. Coronal, axial, and sagittal images displaying intracardiac structures with excellent spatial and contrast resolution were acquired during systole or diastole. It is concluded that MR will be a valuable noninvasive method of diagnosing congenital heart disease.
In anesthetized, open-chest dogs, one burst of stimuli was delivered to the left or right vagus nerve each cardiac cycle. The timing of the stimulus bursts relative to the cardiac cycle was varied by a constant, small amount on successive cardiac cycles, until the entire cardiac cycle was scanned. The level of vagal activity was changed by varying the number of stimulus pulses in each burst; two levels of activity were used in each experiment. For a given level of vagal activity, the mean cardiac cycle length and the amplitude of the phase-response curve were significantly greater during right than during left vagal stimulation. These response characteristics increased as the level of vagal activity was augmented. The minimum-to-maximum phase differences of the phase-response curve were less during right than during left vagal stimulation and when the level of vagal activity was increased. The disparities between the minimum-to-maximum phase differences for the right and left vagi are probably ascribable to the associated differences in the overall magnitudes of the chronotropic responses, rather than to any fundamental difference in the innervation of the effector cells by nerve fibers originating from the right and left sides.
The ability of 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine), a synthetic creatine analog, to protect myocardium during global ischemia was assessed in isovolumic rat hearts using phosphorus-31 nuclear magnetic resonance spectroscopy. Wistar rats were fed a 1% cyclocreatine diet. After 2 weeks, cyclocreatine-fed (n = 8) and control (n = 7) rats were anesthetized, the heart was excised and retrograde perfusion was begun at 10 ml/min per g with 37 degrees C, phosphate-free buffer containing glucose and oxygen. Hemodynamic and spectroscopic data were obtained during baseline, ischemia and recovery periods (each 24 min). During ischemia, the heart of control rats developed a rigor-like increase in tonic pressure (ischemic contracture) not seen in the heart of cyclocreatine-fed rats (22 versus 1 mm Hg, p less than 0.01). This change was associated with significantly more adenosine triphosphate (ATP) at end-ischemia in the cyclocreatine group (1.6 versus 0.6 mumol/g, p less than 0.01) and delayed development of acidosis (p less than 0.001). With reperfusion, the heart of cyclocreatine-fed rats spontaneously defibrillated sooner than did the heart in control rats (178 versus 346 s, p less than 0.03). Diastolic pressure remained significantly elevated throughout recovery in control hearts compared with treated hearts (p less than 0.001). Prior feeding with cyclocreatine preserves myocardial adenosine triphosphate during ischemia, delays the development of acidosis and ischemic contracture and improves recovery of mechanical function on reperfusion.
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