Diagnosis of aortico-pulmonary window by two-dimensional echocardiography.
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Aorta↗
Biomedical subjects
A F Rickards
Publications and source records attributed to A F Rickards.
Effect of intravenous amiodarone on myocardial repolarization and refractoriness: a new method of assessment.
Amiodarone is a benzofuran derivative with depressant effects on all electrically active cardiac tissues and important antiarrhythmic properties after long-term dosing. We evaluated its short-term effects on myocardial repolarization and refractoriness in eight patients. The duration of repolarization was evaluated by a new method, the paced evoked-response system, which records the dominantly local repolarization that follows a controlled (paced) depolarization from the same site. Intravenous amiodarone (5 mg/kg) prolonged the latency of the stimulus peak-evoked T wave interval an average of 39.4 msec (+15% of control) 10 min after infusion. In animal experiments these changes correlated well with simultaneous increases in the paced monophasic action potentials obtained with suction electrode catheters. There was also a lengthening of the effective refractory period of the atrioventricular node from 270 +/- 20 to 295 +/- 25 msec. Atrial and ventricular refractoriness were not altered. Amiodarone early activity at the atrial and ventricular level apparently differs from that long-term therapy and appears to favor changes in action potential duration and not changes in refractoriness.
Action Potentials↗
Rupture of a papillary muscle of the tricuspid valve. Echocardiographic diagnosis.
Abnormal tricuspid valve structure and motion resulting from the rupture of a right ventricular papillary muscle were visualised by two dimensional echocardiography. These findings were confirmed at operation. Two dimensional echocardiography appears to be a satisfactory method for evaluating patients with tricuspid regurgitation of sudden onset with a view to surgery.
Adult↗
Evaluation of drug-induced changes in myocardial repolarisation using the paced evoked response.
The use of the pace evoked response system in the assessment of drug-induced changes in myocardial repolarisation is reported. Using a conventional pacing electrode lead for both pacing and sensing, this system records the dominantly local repolarisation which follows a controlled (paced) depolarisation from the same site. Measurements of the latency of the ventricular evoked response at matched heart rates before and after drug administration permit the accurate direct comparison of the effects of drugs with class 3 mode of action on cardiac muscle repolarisation. Using this method we have evaluated the effect on the timing of the evoked T wave of two drugs which are known to prolong phase 2 of the action potential. Intravenous amiodarone (5 mg/kg) prolonged the stimulus-peak evoked T wave interval by an average of 39-4 ms (15% of control values); three hours after oral bethanidine (2 mg/kg) this interval increased by an average of 25.8 ms (10% of control values). The effect of therapeutic interventions on the latency of the local paced evoked response provides a simple, accurate assessment of their effect on the cellular action potential duration and constitutes a new tool in electrophysiological investigations.
Amiodarone↗
Irreversible morphological changes contributing to depressed cardiac function after surgery for chronic aortic regurgitation.
The timing of surgery in chronic aortic regurgitation remains a difficult problem. To identify variables predictive of postoperative haemodynamic improvement, changes in left ventricular mass, volume, morphology, and histochemistry were analysed in 67 patients undergoing surgery for chronic aortic regurgitation. Patients were divided into two groups: those in whom the left ventricular echo diameters returned to normal after operation (51 patients, group A), and those with postoperative dilatation (16 patients, group B). A preoperative biopsy was obtained in all patients; postoperative tissue samples were available in 13 patients (five from group A, eight from group B). Data were correlated with the postoperative clinical, haemodynamic state over a follow-up period of three years. Regression of hypertrophy was usually incomplete. Echocardiographic and angiographic data could not define the type and degree of dysfunction which was irreversible. Massive fibre hypertrophy (mean 34.1 micrometers), moderately or severely increased interstitial fibrous tissue, reduced levels of the myofibrillar and mitochondrial enzymes adenosine triphosphates and succinate dehydrogenase in pre- and post-operative tissue samples correlated with persistent dilation, cardiac failure, and early death (group B). Irreversible morphological and functional changes contributed to a depressed cardiac function after operation. Preoperative ventricular biopsies are thus of prognostic importance in volume overload.
Adolescent↗
Cardiac pacing.
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Cardiac Pacing, Artificial↗
Relation between QT interval and heart rate. New design of physiologically adaptive cardiac pacemaker.
The relation between QT interval and heart rate has been studied in a group of patients undergoing physiological exercise, in a group undergoing atrial pacing without exercise, and in a group with complete heart block undergoing exercise at a fixed ventricular rate controlled by cardiac pacing. The expected shortening in QT interval during physiological exercise is only in part the result of the intrinsic effect of increased rate, since patients undergoing atrial pacing to comparable rates show only a small decrease in measured QT interval and patients exercising at fixed rates in heart block exhibit a decreasing QT interval related to the independent atrial rate. QT interval changes appear mainly to be governed by factors extrinsic to heart rate. The physiological control of QT interval has been used to construct a cardiac pacemaker which senses the interval between the delivered stimulus and the evoked T wave, and uses the stimulus-evoked T wave interval to set the subsequent pacemaker escape interval. Thus physiological control of cardiac pacing rate, independent of atrial activity, using conventional unipolar lead systems is possible.
Cardiac Pacing, Artificial↗
The relationship between QT interval and heart rate during physiological exercise and pacing.
Conventional doctrine states that the QT interval is related to heart rate in an inverse exponential relationship, so that with increasing rate the QT interval shortens. This relationship has recently been studied in a group of patients undergoing physiological exercise stress tests, atrial pacing stress test, and in a further group of patients with complete heart block undergoing exercise at a fixed ventricular rate controlled by cardiac pacemaker. Examinations of recordings made during physiological exercise do show the expected shortening in QT interval, we believe that this shortening is only in part due to the intrinsic effect of increased rate as patient who were atrially paced to similar rates and within the same age group showed only a small decrease in measured QT interval and patients undergoing exercise at fixed ventricular rate showed shortening in QT interval which was related to the independent atrial rate. It appears, therefore, that the QT interval is governed mainly by extrinsic factors and not intrinsically rate related. The physiological control of QT interval is being used now to construct a cardiac pacemaker which senses the interval between the delivered stimulus and the evoked T wave so that the stimulus-evoked T wave interval could be used to set the subsequent escape interval and subsequently the overall pacing rate. Physiological control of cardiac pacing rate using conventional unipolar lead systems and independent of atrial activity is possible and currently being investigated.
Cardiac Pacing, Artificial↗
Identification of atrial septal defects by cross-sectional contrast echocardiography.
Cross-sectional echocardiography, combined with injections of contrast into peripheral arm veins, has been used to study 15 patients with atrial septal defects and 10 patients with an intact interatrial septum. Of 11 patients with ostium secundum or sinus venosus atrial septal defects and left-to-right shunts a defect could be visualised in all, and in eight some degree of transfer of contrast from right atrium to left atrium was seen. In three of four patients with a dominant right-to-left shunt a defect was seen and in all there was free transfer of contrast from right atrium to left atrium. Though there may be variable loss of echoes in the septal image in patients with an intact interatrial septum, in general no fixed defect is seen an there is no transfer of contrast from right atrium to left atrium. This is a potentially valuable technique in the assessment of patients in whom an atrial septal defect is suspected.
Adolescent↗
R wave amplitude during exercise. Relation to left ventricular function and coronary artery disease.
Change in R wave amplitude (mean delta R) was measured sequentially during and after 12 lead maximal treadmill exercise tests in 14 subjects with normal coronary arteries and 62 patients with coronary artery disease. In normal subjects mean delta R decreased maximally one minute after exercise and returned to control levels within three minutes. In contrast, mean delta R increased in patients with coronary artery disease, the greatest change occurring in patients with either triple vessel or left main disease or those with an akinetic region on the left ventriculogram. R wave amplitude returned to resting levels in five minutes. Increase in R wave amplitude was not directly related to changes in the ST segment. Changes in R wave amplitude during maximal treadmill exercise may improve the discrimination between patients with and without coronary artery disease and may help to identify those patients with abnormal left ventricular function.
Adult↗
Maximal 12-lead exercise testing for prediction of severity of coronary artery disease.
Ninety-three patients with chest pain underwent both maximal 12-lead treadmill testing and coronary arteriography to ascertain whether exercise testing might predict multivessel coronary disease. Twenty-eight patients had normal coronary arteries, 20 single vessel disease (greater than 70% reduction in luminal diameter), 18 double and 22 triple vessel disease. Five patients had left main coronary disease. All 45 patients with double, triple or left main disease had positive 12-lead exercise tests whilst only 15/20 (75%) with single vessel disease had positive tests. Sensitivity of the 12-lead electrocardiogram during maximum stress testing was 92%, with 15% false negatives. The predictive value of a positive test was 100% (no false positives) and 85% for a negative test. Significant predictors of severe triple vessel and left main coronary disease were the sum of ST segment depression (xi ST), the number of ECG leads which developed ST segment depression, the stage at which ST depression developed and the ST segment recovery time. There was a significant correlation between the anatomical location of coronary artery stenoses and the area of ischaemia indicated by the exercise electrocardiogram.
Adult↗
Routine exercise testing in angina pectoris.
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Angina Pectoris↗
Hemodynamic effects of intravenous metoprolol.
The hemodynamic effects of the cardioselective beta adrenergic blocking agent metoprolol, at a dose of 0.1 mg/kg body weight administered intravenously, were studied in 10 patients undergoing routine cardiac catheterization. The beta adrenergic blocking effect of the drug was confirmed by a highly significant reduction (53 percent, P less than 0.001) in the mean heart rate response to a challenge with isoproterenol, and by a mean heart rate rssponse to a challenge with isoproterenol, and by a highly significant reduction (73 percent, P less than 0.001) in the isoproterenol-induced increase in the first derivative of left ventricular pressure (dP/dt). An intrinsic negative inotropic effect was shown by a 43 percent reduction (P less than 0.05) in the response of mean left ventricular dP/dt when the heart rate was fixed by atrial pacing alone. With the combination of atrial pacing and isoproterenol, metoprolol produced a 48 percent reduction (P less than 0.01) in the response of mean left ventricular dP/dt, resulting from both the intrinsic depressor effect and the beta adrenergic blocking effect on the rate-independent beta agonist activity of isoproterenol. There was no significant change in right atrial, femoral arterial or left ventricular end-diastolic pressure; analysis of left ventricular angiograms performed during atrial pacing before and after metoprolol revealed no significant effect on angiographic ejection fraction, pressure-volume loops or diastolic compliance. In two patients improvement in segmental wall motion was noted, and no deterioration was seen in any patient. Metoprolol is an effective cardioselective beta adrenergic blocking agent that, under these conditions, reduces catecholamine-induced increases in heart rate and left ventricular dP/dt without significant alteration in ejection fraction, preload or afterload.
Adult↗
Isolated congenital absence of coronary sinus.
A case is reported in which contrast angiography showed complete absence of the coronary sinus, the cardiac veins draining separately into left and right atria. Normal systemic venous drainage was demonstrated by contrast cross-sectional echocardiographic methods and later confirmed by conventional angiographic injections. In addition, angiography showed a stenosis in the anomalous cardiac vein draining into left atrium accounting for the presence of a continuous murmur for which the patient was initially referred.
Angiocardiography↗
Observations on the effect of angina on the left ventricle, with special reference to diastolic behavior.
A series of investigations on patients developing angina following pacing are described. Evidence suggesting tension prolongation in the ischaemic areas of the ventricle with reduction in segmental systolic inward movement and a decrease in segmental diastolic complicance is presented and discussed.
Angina Pectoris↗
[Hemodynamic comparison of Starr-Edwards, Lillehei-Kaster and homograft valves in the mitral position (author's transl)].
In 16 patients with Starr-Edwards (SE) disc valves, 10 patients with Lillehei-Kaster (LK) valves, and 4 patients with fresh aortic homografts (HG) in the mitral position the hemodynamic qualities of the valves were studied. All three valve types in general showed similar results, but they differed clearly as far as special parameters are concerned. So SE valves had the highest pressure gradients, HG valves the lowest, whereas LK valves were in between. The results of the study lead to the conclusion that tilting disc valves implanted in the mitral position are the best compromise, since they are always available and their hemodynamic response can be tolerated.
Angiocardiography↗
[Letter: Blood pressure determination in mm Hg or kilopascal?].
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Blood Pressure Determination↗
Effect of isoprenaline and nitroglycerine on pressure time indices and coronary graft blood flow in man.
In five patients studied 1 to 3 d after coronary artery surgery isoprenaline and nitroglycerine have been used to alter the systolic (TTI) and diastolic (DPTI) pressure time indices. A close correlation with the predicted relationship between diastolic coronary graft flow and the DPTI/TTI ratio has been demonstrated during isoprenaline-induced tachycardia. Nitroglycerine reduced diastolic coronary graft resistance and increased the DPTI/TTI ratio, effects which are desirable for the relief of angina.
Adult↗