The use of halothane in a patient with asymmetrical septal hypertrophy: a case report

An elderly patient with demonstrated asymmetrical intraventricular septal hypertrophy and ventriculo-aortic pressure gradient was anaesthetized with nitrous oxide with oxygen, narcotic, and muscle relaxant for abdominal surgery. In addition to the cardiovascular variables customarily monitored, a systolic time interval (STI) measured from the Q wave of the ECG to the foot of the radial pulse (the QF interval) was calculated in milliseconds beat-to-beat by a computer. With anaesthesia, and particularly following the beginning of operation, the QF interval lengthened as an indication of either decreased cardiac inotropy or increased pressure gradient across the aortic outflow tract. When halothane 0.25 per cent was added to the anaesthetic mixture, the QF interval shortened by about 20 milliseconds without an observed change in direct arterial pressure. Since halothane is a cardiac depressant and normally lengthens the STI, it apparently relaxed the muscular stenosis of the ventricular outflow tract and reduced the pressure gradient and, subsequently, the QF interval. By measuring cardiovascular function with this STI, the beneficial action of cardiac depression from low-dose halothane was observed, which would have escaped detection by common monitoring indices.