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K S Ng

Publications and source records attributed to K S Ng.

5 recordsLinked to original sources

Relation of filling pattern to diastolic function in severe left ventricular disease.

M mode and Doppler echocardiograms, apex cardiograms, and phonocardiograms were recorded in 50 patients with severe ventricular disease of varying aetiology to examine how left ventricular filling is disturbed by cavity dilatation. The size of the left ventricular cavity was increased in all with a mean (SD) transverse diameter of 7.2 (0.8) cm at end diastole and 6.3 (0.8) cm at end systole. All were in sinus rhythm and 35 had functional mitral regurgitation. In nine patients, in whom filling period was less than 170 ms, transmitral flow showed only a single peak, representing summation. In the remainder there was a strikingly bimodal distribution of filling pattern. In 12 the ventricle filled dominantly with atrial systole (A fillers). Isovolumic relaxation was long (75 (35) ms) and wall motion incoordinate; mitral regurgitation was present in only one. In most (29) the left ventricle filled predominantly during early diastole (E fillers). Mitral regurgitation, which was present in 26, was much more common than in the A fillers, while the isovolumic relaxation time (10 (24) ms) was much shorter and the normal phase relations between flow velocity and wall motion were lost. In 24 E fillers no atrial flow was detected. In four there was no evidence of any mechanical activity, suggesting "atrial failure". In 20, either the apex cardiogram or the mitral echogram showed an A wave, implying that atrial contraction had occurred but had failed to cause transmitral flow, showing that ventricular filling was fundamentally disturbed in late diastole. A series of discrete abnormalities of filling, beyond those shown by Doppler alone, could thus be detected in this apparently homogeneous patient group by a combination of non-invasive methods. The presence and nature of these abnormalities may shed light on underlying physiological disturbances.

Blood Flow Velocity

Malignant hyperthermia.

Two cases of malignant hyperthermia (MH) are presented. The first patient presented initially with tachyarrhythmia intraoperatively and rapid onset of MH crisis. Nasopharyngeal temperature of 43 degrees C was attained after 15-20 minutes of anaesthesia. The patient eventually died of myocardial failure despite external cardiac massage, inotropic support and ventricular pacing. The second patient presented with increasing endogenous hypercarbia following the administration of suxamethonium and isoflurane. The use of the end tidal carbon dioxide monitor led to an early diagnosis of MH. The early use of dantrolene may have contributed to the favourable outcome.

Adult

Impairment of diastolic function by shortened filling period in severe left ventricular disease.

A dilated left ventricle with reduced ejection fraction is usually attributed to impaired systolic function. To investigate the possibility that ventricular filling might also be disturbed, M mode echocardiograms, phonocardiograms, and Doppler cardiograms were recorded in 30 patients with ventricular disease of varying cause. All but four had functional mitral regurgitation. The size of the left ventricular cavity was increased in all and peak velocity of circumferential fibre shortening was reduced. Diastolic abnormalities included a short isovolumic relaxation time, and, on digitised M mode, a reduced rate of dimension increase and of posterior wall thinning. Although the timing of aortic valve closure was normal, mitral regurgitation persisted beyond it by 95 (35) ms and beyond mitral valve opening by 60 (40) ms. This reduced the effective filling time (the interval when the mitral valve was open and mitral regurgitation was absent) to less than 200 ms in seven patients. The effective filling time correlated closely with the RR interval, the regression equation indicating a reduction of 80 ms for each 100 ms fall in RR interval. It was also independently shortened by 2 ms a year with increasing age. The effective left ventricular filling time may thus be very short in patients with left ventricular cavity dilatation and functional mitral regurgitation. It is suggested that when diastolic function is also abnormal, this short filling time may physically limit ventricular inflow. Its close relation to heart rate might contribute to the therapeutic effect of beta blockade in such patients.

Adolescent