Biomedical subjects
Publications and source records attributed to J C Crick.
A case report of a midpalmar abscess from Mycobacterium fortuitum is presented. It appeared 4 weeks after a penetrating nail injury to the palm and wrist and resolved with chemotherapeutic and surgical treatment.
Baseline variables in 300 coronary angioplasty procedures were analysed to identify factors predictive of a successful outcome. Separate multivariate analyses distinguished between predictors of primary angiographic success and functional success as determined by the results of predischarge treadmill stress electrocardiography. Three independent predictors of primary angiographic success were identified: number of balloon inflations per procedure, initial stenosis, and operator experience. Of these, the number of balloon inflations per procedure and operator experience were also predictive of functional success, reflecting the dependence of a good functional result on a successful procedure. Other independent predictors of functional success were the severity of the residual stenosis and single vessel coronary artery disease suggesting that adequacy of revascularization is an important determinant of the functional result. These data illustrate the interaction between clinical, angiographic and functional variables in determining the success of PTCA. A good angiographic result may not translate into a good functional result if revascularization is incomplete.
Eight patients with the Siemens Elema "Tachylog" generator implanted for management of paroxysmal reentrant tachycardia were studied to assess the safety and efficiency of three antitachycardia programs. The programs investigated were burst overdrive, self-searching, and adaptive table scanning. There were five males and three females aged 19-62 years. Seven had Wolff-Parkinson-White syndrome, and one had dual atrioventricular nodal pathways. Four had right atrial electrodes and four had right ventricular electrodes. Patients were studied lying, standing, and exercising in all three modes, and the appropriate long-term programs were chosen. The generator remained in a program for 1 month, it was interrogated and the memory was read, and then it was reprogrammed to a different antitachycardia mode. Burst overdrive was unsuitable for long-term use in four patients, producing atrial fibrillation in one and ventricular arrhythmias in three. In this group, self-searching and adaptive table scanning were safe and equally effective (mean number of attempts/tachycardia 6.97 and 6.3, respectively). In the four patients in whom all three programs could be used, burst overdrive proved to be most efficient, the mean number of attempts/tachycardia were 2.4 (cf 9.6 and 9.0 for self-searching and adaptive table scanning). Thus, burst overdrive was only suitable for long-term use in 50% of our patients, but when safe it was more efficient than the other two programs, especially in those with narrow termination windows on exercise.
In a consecutive series of 400 patients treated by percutaneous transluminal coronary angioplasty 212 had single vessel disease, 142 had multivessel disease with only one vessel dilated, and 46 had multivessel dilatation. In addition sequential stenoses were dilated in the same vessel in all groups. There was no mortality among patients with single vessel disease. Success rates varied from 83% to 90% according to the artery in which angioplasty was attempted. Urgent surgery was required by 3.8%. Primary success was lower (74%) in the presence of multivessel disease and complications were more frequent, with four deaths (2.8%). In 46 patients with multivessel disease in whom all important lesions were dilated during the same procedure the overall primary success rate was 76% and within the last year of the study it was 91%. One (2%) patient died and three (7%) required urgent surgery. Twelve (86%) out of 14 stenosed vein grafts were successfully dilated and eight (53%) chronically occluded vessels were re-opened; in both groups there were no deaths, no infarctions, and no need for urgent surgery. In all groups symptoms improved greatly and predischarge exercise tests showed that there was no reversible ischaemia in 94% of patients with single vessel disease or in 65% of patients with incomplete revascularisation. Six months after the procedure 95% of the patients had improved symptomatically and 80% had normal exercise tests after one year. Percutaneous transluminal coronary angioplasty is the method of choice in single vessel disease and its use also results in a high proportion of other patients becoming symptom free. Complication rates are low and for selected patients results that are equivalent to those of cardiac surgery are obtained.
Plastic responses of plants to environmental factors may be placed in an ecological context by regarding them as components of sets of traits which are predictably related to habitat stability and productivity. In ephemeral plants of temporary habitats plasticity is a major component of the mechanisms which tend to sustain reproduction when these plants are exposed to stress. When perennials of more stable habitats are subjected to stress the most frequently observed effect of plastic changes in allocation is to defer reproduction, a mechanism which appears to safeguard survival of the parent plant. It is suggested that plasticity is of vital importance in resource acquisition by plants. This hypothesis is supported by the results of experiments in which the roots and shoots of plants of contrasted ecology have been subjected to controlled patchiness in resource supply. We conclude that in plants of productive habitats high morphological plasticity is part of the foraging mechanisms which project new leaves and roots into the resource-rich zones of the constantly changing environmental mosaic created by the activity of competing plants. In long-lived plants of chronically unproductive habitats plasticity is expressed primarily through reversible physiological changes. These appear to maintain the viability and functional efficiency of leaves and roots over their long life spans and facilitate exploitation of the pulses of temporary and unpredictable resource supply which are characteristic of unproductive habitats.
This study was performed to ascertain whether intravenous amiodarone would revert supraventricular tachycardias to sinus rhythm, and if so, whether this effect depended upon the underlying mechanism of the arrhythmia. Fourteen patients were studied. Seven had Wolff-Parkinson-White (WPW) syndrome, 1 had dual atrioventricular nodal pathways and 1 an ectopic atrial tachycardia. Five patients had atrial fibrillation without accessory pathways. An atrial electrode was inserted to initiate tachycardias and record the electrogram. If tachycardias were stable for more than 5 min, amiodarone (5 mg/kg) diluted with dextrose saline was infused intravenously over 5 min. Two electrocardiographic leads and the right atrial electrogram were monitored. In 7 patients with atrial fibrillation (2 with accessory pathways), 6 did not revert to sinus rhythm, 1 reverted only after 1 hr. In 5 cases without accessory pathways the ventricular rate fell 5-10 min after commencing amiodarone. Four of the 5 patients with WPW syndrome and re-entrant tachycardias returned to sinus rhythm within 6 min of commencing the infusion (atrioventricular and ventriculoatrial times increased by 0-38% and 0-14% respectively). (Tachycardias terminated in the anterograde limb.) Three patients underwent intermittent right atrial stimulation for 1 hr. No tachycardias could be initiated for 30 min post amiodarone. The ectopic atrial tachycardia and that due to dual atrioventricular nodal pathways terminated within 7 and 2 min, respectively, of commencing intravenous amiodarone. Thus the use of intravenous amiodarone would be appropriate in the acute management of sustained supraventricular tachycardias.
In a study of the concept of pacemaker dependence, 86 patients who had permanent ventricular demand (VVI) pacemakers implanted for more than six months and were in predominantly paced rhythm underwent repeated interruption of pacing both abruptly and after gradual reduction of paced rate. Non-invasive pace slowing was accomplished by timed inhibiting pulses applied to the chest wall. The results identified a small group (A) of patients, 8% of those tested, who consistently failed to develop an adequate escape rhythm and may thus be considered highly pacing dependent. A second group B, 26%, developed an adequate intrinsic rhythm with serial decremental rate inhibition (SDRI) but suffered symptoms with abrupt complete inhibition (ACI). The remaining 66%, group C, developed no symptoms in any test. Analysis of clinical pre-test data showed that syncope, atrioventricular block and a low rate prior to implant, and a long duration of pacing were associated with a higher degree of pacing dependence, but were not reliably predictive. The clinical significance and value of the results are discussed. We conclude that SDRI is a reliable test for the high degree of pacemaker dependence and can be helpful especially in planning a procedure which may involve interruption of pacing.
High energies delivered via standard pacing catheter electrodes produce permanent atrioventricular conduction block and generate high pressures. We investigate the use of lower energies and an active fixation electrode. Ten patients with refractory supraventricular tachycardias (six with paroxysmal atrial fibrillation, three with dual AV nodal pathways, and one with a concealed accessory atrioventricular pathway) were treated. A 6F Vitatron Helifix electrode was positioned to give the maximum His bundle deflection. Four shocks of only 50 joules each were delivered at 1-minute intervals. Long-term follow-up showed that seven patients (70%) had persistent complete heart block and two had atrial fibrillation with slower ventricular rates. Nine patients (90%) were symptom-free without antiarrhythmic therapy. Permanent pacemakers were implanted in eight patients. There were no complications resulting from the procedure. Transvenous ablation of atrioventricular conduction can be safely achieved using a Vitatron Helifix electrode and much lower energy values than have been previously employed.
Ten patients with Wolff-Parkinson-White syndrome underwent cardiac electrophysiological study extended to include the induction of atrial fibrillation at maximum exercise in the upright position. This was performed using a new temporary bipolar lead with a helical active fixation tip for atrial pacing. The highest rate of atrioventricular conduction via the accessory pathway was greater during exercise than at rest in all 10 patients (mean increase 28%). In three cases the resulting ventricular rate exceeded 300 beats/min, but no patient had severe symptoms or ventricular arrhythmias. The exercise induced enhancement of accessory pathway conduction may significantly but unpredictably affect the risk from spontaneous atrial fibrillation especially in patients with coronary artery disease or in those taking antiarrhythmic drugs. The test procedure was sufficiently simple and well tolerated to be included in our routine electrophysiological investigation.
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Thirty patients undergoing cardiac catheterisation for coronary artery disease received parenteral ajmaline (15 patients) or prajmaline (15 patients). There were no statistically significant induced changes in left ventricular systolic or end diastolic pressures, indirect left atrial pressure, pulmonary artery mean pressure, cardiac output or left ventricular ejection fraction compared to control values. Intravenous prajmaline bitartrate in 15 patients with angina did not significantly alter work capacity, maximum exercise heart rate or systolic blood pressure compared to control values. Five patients developed transient minor conduction defects ( 2LBBB , 1 RBBB, 2 prolonged PR interval): all five were also receiving long-term treatment with beta blockers and nifedipine.
The case is presented of a young patient with atrioventricular (AV) block but no evidence of other disease; in this patient exercise or stress-related syncope continued after implantation of a ventricular inhibited (VVI) pacemaker. Investigation revealed exercise-induced limited rapid multiform ventricular tachycardia (VT) which was associated with faintness or syncope. Temporary atrial triggered ventricular inhibited ventricular (VDD) pacing resulted in enhanced exercise tolerance with no significant arrhythmia. A permanent full function dual chamber (DDD) pacemaker was implanted and prevented the VT. There have been no further exercise-related symptoms during two years of follow up.
A pacing system requiring only a single lead was used to establish atrial synchronised pacing in eight patients with complete atrioventricular block and cardiogenic shock following acute myocardial infarction. Spontaneous atrial activity was sensed through electrodes positioned on the pacing lead and used to trigger ventricular demand pacing. A normal atrioventricular relation could be established in each of these critically ill patients without the complexity of inserting and finding a stable position for an additional atrial sensing lead. Atrial synchronised pacing at the spontaneous sinus rate had distinct haemodynamic advantages compared with conventional ventricular pacing at 100 beats/min. Mean cardiac output for the group was 3.3 1/min with atrial synchronised pacing compared with 2.6 1/min with conventional pacing, a significant difference of 27%. Peak systolic pressure averaged respectively 91 and 73 mm Hg in the two pacing modes. With conventional ventricular pacing a pronounced phasic alteration in blood pressure was observed, dependent on the altering relation of the paced beats to spontaneous atrial activity. Atrial synchronised pacing abolished this effect and resulted in a stable blood pressure at or above the peak pressure achieved with conventional pacing. Atrial synchronised pacing with a single lead system can be established rapidly. This mode of pacing has appreciable and significant haemodynamic superiority over conventional ventricular pacing in patients with cardiogenic shock and atrioventricular block following acute myocardial infarction.
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Twenty-four patients have been treated for periods of up to two years (mean 14 months) with this single pass electrode for physiological pacing. Manufacturing refinements now allow percutaneous insertion into the subclavian vein. Pacing thresholds and sensing signals from both atrium and ventricle have remained satisfactory for a wide variety of different physiological pacemakers. No complications specifically related to the lead have occurred in a total of 277 patient months. We conclude that this single pass electrode is suitable for long-term implantation and can provide physiological pacing with present day stimulators.
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