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Biomedical subjects

M Dick

Publications and source records attributed to M Dick.

At least 73 records · Page 4Linked to original sources
PubMed1989

Repair of truncus arteriosus in the neonate and young infant.

Infants with truncus arteriosus present a difficult management issue. Because of the high operative mortality, repair is often delayed beyond the first 3 to 6 months of age. We reviewed our experience with 11 neonates and young infants with truncus arteriosus undergoing repair (median age, 21 days). Five patients also had major truncal valve insufficiency, and 2 required valve replacement. Right ventricle-pulmonary artery continuity was established with a porcine valved conduit in 3 patients and an aortic or pulmonary homograft in 8. There was 1 operative death (9%; 70% confidence limits, 3%-22%) and 1 late death over a mean follow-up of 21 months (range, 4 to 32 months). Eight of the 9 late survivors are growing normally. Echocardiographic examination revealed normal ventricular function in all patients (mean shortening fraction, 39%). Doppler assessment demonstrated trivial prosthetic or homograft valve regurgitation in 7 patients and mild to moderate obstruction in 5 patients. This recent experience with repair of truncus arteriosus indicates that the operative risk is low even in the neonate. Repair in the first month of life should be recommended before the development of critical congestive heart failure or irreversible pulmonary vascular disease.

Abnormalities, Multiple↗
PubMed1989

Concealed anterograde accessory pathway conduction during the induction of orthodromic reciprocating tachycardia.

The purpose of this study was to determine whether concealed anterograde accessory pathway conduction occurs during the induction of orthodromic tachycardia by an atrial extrastimulus (S2). Sixteen patients with an overt (n = 9) or concealed (n = 7) accessory pathway had inducible orthodromic tachycardia by S2 during an atrial drive (S1) cycle length of 500 to 650 ms. A ventricular extrastimulus (S3) was introduced coincident with the His depolarization resulting from S2 during the longest S1S2 interval that reproducibly induced orthodromic tachycardia. The S1S3 interval was decreased in 10 ms steps until S3 reached ventricular refractoriness. Retrograde accessory pathway conduction of S3 in the presence and absence of S2 was compared at the same S1S3 intervals. In the absence of S2 there was retrograde accessory pathway conduction after S3 in each patient. In the presence of S2, in patients with overt pre-excitation, retrograde accessory pathway conduction after S3 was absent in one patient, prolonged in four patients and present only after long S1S3 intervals in three patients. Only one patient had unchanged retrograde conduction regardless of the presence or absence of S2. In patients with a concealed accessory pathway, retrograde accessory pathway conduction after S3 was absent in five patients and was prolonged in two. Thus, concealed anterograde accessory pathway conduction was present in 15 of 16 patients at the time of orthodromic tachycardia induction. In conclusion, concealed anterograde accessory pathway conduction occurs in a majority of patients with an overt or a concealed accessory pathway during induction of orthodromic tachycardia by an atrial extrastimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Psychosocial responses of children to cardiac pacemakers.

To examine the psychosocial responses of children and adolescents with a cardiac pacemaker and compare their responses to those of their peers, we evaluated 30 pediatric pacemaker patients, aged 7 to 19 years, and two age- and sex-matched comparison groups, including 30 patients with similar heart disease but without pacemakers and 30 physically healthy children, using standardized psychometric tests and a specific interview format. We postulated that children with pacemakers would experience greater stress in psychosocial adaptation. No significant differences on standardized measures of trait anxiety, self-competence, or self-esteem were found between the pacemaker group and the comparison groups. In contrast, pacemaker subjects were significantly (p less than 0.05) more external in their locus-of-control orientation than were healthy subjects, suggesting a diminished sense of personal control and less autonomy. Pacemaker subjects, particularly the older ones, had significantly (p less than 0.05) greater knowledge of pacemaker systems than did subjects in the other two groups, facilitating the use of intellectualization as a coping mechanism. The pacemaker patients were likely to be as fearful of social rejection as of potential pacemaker failure. All three groups identified potential negative peer reactions toward an individual with a pacemaker. The patients with cardiac disease but without pacemakers and the healthy subjects perceived significant (p less than 0.05) social and emotional differences between patients with pacemakers and their peers, but the pacemaker patients did not view themselves as different from their peers. This study demonstrates healthy psychosocial adaptation of children with cardiac pacemakers. Although these children appear to cope effectively with the stress of their life situation through the use of denial and intellectualization, they may experience problems both in the development of autonomy and in social isolation and rejection.

Adolescent↗
PubMed1989

Transcatheter electrical ablation of accessory pathways in children.

Supraventricular tachycardia (SVT), the most common sustained symptomatic arrhythmia of childhood, is often supported by a manifest or concealed accessory pathway. Permanent interruption of the accessory pathway usually requires surgical division. Recent experience with electrical ablation of posterior septal pathways in adults prompted us to apply the technique to children. Six children, ages 8 to 15 years, underwent a complete electrophysiological study followed by transcatheter electrical ablation. Five of the 6 children, 3 with a right posterior septal and 2 with a left posterior septal pathway, were approached with the ablation catheter at the os of the coronary sinus. In the remaining patient, a left lateral pathway was mapped with an electrode catheter in the coronary sinus and then approached with the ablation catheter through the patent foramen into the left atrium. Two patients are asymptomatic 18-24 months postablation; one patient had return of anomalous conduction between 7 and 21 days after ablation. Two patients had transient interruption of anomalous conduction, whereas one patient experienced no effect. We conclude that in carefully selected patients, transcatheter electrical ablation offers an alternative to surgery for permanent interruption of an accessory pathway.

Adolescent↗
PubMed1989

Long-term results of catheter ablation of a posteroseptal accessory atrioventricular connection in 48 patients.

Forty-eight patients with a posteroseptal accessory atrioventricular (AV) connection underwent catheter ablation of the accessory AV connection with 200-400 J shocks delivered by a standard defibrillator. Cathodal shocks were delivered through the proximal pair of electrodes of a 6F quadripolar electrode catheter positioned in the coronary sinus such that the proximal electrodes straddled the ostium (12 patients) or the third electrode from the tip was at the ostium (36 patients). A 16-cm patch electrode positioned on the back or anterior chest served as the anode. Two to 4 shocks were delivered (total, 635 +/- 198 J, mean +/- SD). The cathether ablation procedure was clinically successful in eliminating symptomatic tachycardias in in 32 of 48 patients (67%) during a mean follow-up of 26 +/- 19 months. A long-term follow-up electrophysiology study was performed in 27 of the 32 patients who had a successful clinical outcome, and this showed that conduction through the accessory AV connection was completely absent in 25 patients and present but impaired in two patients. The success rate was significantly higher in patients with a concealed accessory AV connection (13 of 13, 100%) than in patients with manifest preexcitation (19 of 35, 54%; p less than 0.001). Among the 12 patients in whom the proximal electrodes of the ablation catheter straddled the ostium of the coronary sinus, one patient developed cardiac tamponade requiring needle pericardiocentesis; there were no instances of cardiac tamponade among the 36 patients in whom the third electrode from the tip was at the ostium of the coronary sinus. Other complications were AV block requiring a permanent pacemaker and transient atrial tachycardia in one patient each and an asymptomatic pericardial effusion in three patients. In conclusion, with the catheter ablation technique described in this study, a successful clinical outcome may be achieved in approximately two thirds of patients who have a posteroseptal accessory AV connection, and the risk of serious complications is low. This technique is particularly well suited to patients with a concealed posteroseptal accessory AV connection, in whom the success rate is higher than in patients with manifest preexcitation.

Adult↗
PubMed1989

Sequence of the variant thyroxine-binding globulin of Australian aborigines. Only one of two amino acid replacements is responsible for its altered properties.

A form of thyroxine-binding globulin (TBG) with reduced affinity for hormone and increased susceptibility to heat and acid denaturation has been identified in Australian Aborigines (TBG-A). Results of heat denaturation of TBG established that the TBGA allele is X linked and has a frequency of 50.9% in Western Australian Aborigines. The sequence of an isolated TBGA allele differed at two positions from that of the normal TBG allele (TBGC). One substitution was in codon 191, ACA (threonine) rather than GCA (alanine), and the other was in codon 283, TTT (phenylalanine) instead of TTG (leucine). These nucleotide substitutions resulted in the loss of sites for the enzymes Bgl 1 and Tth 111 II, respectively. The nucleotide substitutions in the TBG-A allele was confirmed by digestion of genomic DNA segments amplified using the polymerase chain reaction. The Bgl 1 and Tth 111 II sites were absent in the genes of two Aboriginal men expressing TBG-A and were present in those of three Aboriginal and six Caucasian males expressing TBG-C. The TBG gene of a seventh Caucasian male possessed the Bgl 1 site but had lost the Tth 111 II site; sequencing of this allele revealed only the substitution in codon 283 identical to that in the TBGA allele. As the biochemical properties of TBGPhe-283 expressed by this individual were indistinguishable from normal TBGLeu-283, we believe that the abnormal properties of TBG-A are due to substitution of alanine for threonine at residue 191.

Adolescent↗
PubMed1989

Visual orientation estimation.

A systematic error is reported in orientation estimation, in that on average, estimates are closer to the vertical axis than are the stimuli by up to 6 degrees. This systematic error results from a specific mechanism that may be related to depth perception, and that is avoided in certain circumstances or when other mechanisms take over. For example, the estimates of one observer who was a well-trained professional draughtsman did not show this systematic error. Furthermore, for all observers tested, estimation of clock time is not subject to the regular orientation estimation error. Rather, observers tend to estimate times as slightly further from the quarter hour than they really are. Orientation judgement channel capacity was also studied under various conditions. The number of discriminable orientations is far above the magic number "7" limit, reaching over 20 in optimal circumstances. The distribution of discriminable orientations is nonlinear, in that these are more closely packed about the horizontal and vertical axis than at the oblique.

Attention↗
PubMed1988

Surgical management of children and young adults with the Wolff-Parkinson-White syndrome.

The Wolff-Parkinson-White syndrome, as originally described, includes palpitations, tachycardia, and an abnormal electrocardiogram (short PR interval and wide QRS complex). The clinical manifestations are dependent upon a reentrant tachycardia supported by an accessory connection bridging the atrioventricular junction and frequently appear during the first two decades of life. Palpitations are the usual symptoms; less frequently, severe symptoms, such as syncope and sudden death, may result from very rapid atrioventricular conduction across the accessory connection during atrial fibrillation. We report the surgical management of 30 young patients with this syndrome, including 6 with life-threatening tachycardia. Surgical interruption of the accessory connection(s) was curative in 90% (27/30) of the patients; life-threatening symptoms were eliminated in the other three. Based on the limited knowledge of the natural history of the Wolff-Parkinson-White syndrome, the individual patient symptoms, and the electrophysiologic properties of each patient's accessory pathway(s), an algorithm is presented outlining the treatment options. This experience strongly suggests that surgical treatment of the Wolff-Parkinson-White syndrome is safe, effective, and possibly the preferred treatment for this disorder in selected young symptomatic patients.

Adult↗
PubMed1988

Atrial pacing to estimate total sinoatrial conduction time in children.

No data exist concerning the total sinoatrial conduction time (TSACT) in children that compare values determined by the atrial extrastimulation technique (TSACTS) with those generated by the atrial pacing method (TSACTN). In this study, TSACT in 55 patients, age 0.2-18.5, was measured using both techniques. TSACTN was performed at a mean 90% (TSACTN-90) (n = 32) or a mean 95% (TSACTN-95 and (n = 38) of sinus cycle length (SCL). When data generated during determination of TSACTN-90 and TSACTS were compared, SCL and recovery cycle length (REC) were similar for both techniques. Likewise, TSACTS (128 +/- 40 ms) and TSACTN-90 (126 +/- 74 ms) were not significantly different. Coefficient of correlation was r = 0.82, p less than 0.001. Chi-square analysis demonstrated a strong association of normal and abnormal values between TSACTS and TSACTN-90. In contrast, when values generated during TSACTN-95 and TSACTS were compared, TSACTS exceeded TSACTN-95 (137 +/- 38 vs 105 +/- 58 ms; p less than 0.001). Values for SCL and REC were similar while correlation between TSACT determined by the two techniques remained strong (r = 0.82, p less than 0.001). Despite a good correlation between TSACTN-90 and TSACTS, individual differences in magnitude and direction were noted between the two techniques. In summary, TSACTN-90 approximates TSACTS in children. TSACTN-90 is preferable to TSACTN-95, probably due to more complete sinus node capture during atrial pacing. However, the behavior of the sinus node in response to extrastimuli (single or train) precludes favoring one technique over the other. More precise evaluation of sinoatrial conduction will require direct recording of sinus node activity.

Adolescent↗
PubMed1988

Comparison of single and double balloon valvuloplasty in children with aortic stenosis.

To compare the effectiveness of the single and double balloon techniques, the short-term results of percutaneous balloon valvuloplasty were assessed in two consecutive groups of children with valvular aortic stenosis. In 16 children (aged 3 months to 17 years) the single balloon technique was utilized; the ratio of balloon diameter to valve anulus diameter was 0.96 +/- 0.03 (mean +/- SEM). In 11 children (aged 3 months to 21 years) the double balloon technique was utilized in which two balloons are positioned across the valve and inflated simultaneously; the ratio of the balloon diameter sum to valve anulus diameter was 1.32 +/- 0.05. The groups were similar in age, weight, cardiac output, prevalvuloplasty gradient and valve anulus diameter. Overall, valvuloplasty reduced the peak systolic gradient by 53% from 80 +/- 4 to 38 +/- 3 mm Hg (p less than 0.0001). In the single balloon group the gradient decreased from 82 +/- 6 to 46 +/- 4 mm Hg (p less than 0.0001), whereas in the double balloon group the gradient decreased from 76 +/- 5 to 26 +/- 4 mm Hg (p less than 0.0001). The peak systolic gradient after valvuloplasty was 43% lower in the double balloon group (p less than 0.01). Furthermore, the single balloon technique reduced the gradient by an average of 43% compared with a 67% reduction with the double balloon technique (p less than 0.001). The short-term complications of valvuloplasty were similar, with an increase in aortic insufficiency occurring in three children in each group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Obstruction to left coronary artery blood flow secondary to obliteration of the coronary ostium in supravalvular aortic stenosis.

Supravalvular aortic stenosis is characterized by obstruction of the left ventricular outflow tract distal to the aortic valve, and may result in diminished coronary artery blood flow. This report describes the cases of 2 patients in whom obstruction to left coronary artery flow was caused by obliteration of the coronary ostium itself. This mechanism differs from the more commonly recognized cause--valve leaflet adhesion to the obstructing ridge of aortic tissue. The coronary artery obstruction found in these 2 patients required direct enlargement of the left coronary ostium in both. This mechanism of impaired coronary artery flow deserves emphasis, as traditional methods of extended patch aortoplasty may fail to relieve the coronary ostial narrowing.

Aorta↗
PubMed1988

Interactions in the discrimination and absolute judgement of orientation and length.

An asymmetric model is described for interactions in the perception of two dimensions (length and orientation) of a single visual stimulus. Two methods were used to test these interactions, and models for the interpretation of the possible outcomes of these tests are discussed. A length discrimination task showed facilitation (decreased reaction time) when orientation was covaried with length, and interference (increased reaction time) when random orientation variation was introduced. A smaller effect was seen when length was varied in an orientation discrimination task in a correlated or random fashion. Analysis of sequential effects showed that reaction times are fastest on repetition trials and are slowed by either the need to change the response or the need for additional sensory processing. With the second method, it was found that the amount of information transmitted in the estimation of orientation was not affected by the introduction of the redundant dimension of length, but that there was a significant gain in the amount of information transmitted in the estimation of length by the addition of the redundant dimension of orientation. It is concluded that orientation is probably a perceptual primitive of the visual system whereas length is a computed variable.

Adult↗
PubMed1988

Endotoxinaemia in sickle cell disease.

Fifty-nine children with sickle cell anaemia (HbSS) or associated haemoglobinopathies were studied prospectively using a chromogenic Limulus amoebocyte lysate assay to detect circulating endotoxin. The 41 children with HbSS (mean age 8 years 9 months) had more serious disease than the 18 with HbSC disease (n = 14) or HbS-beta-thalassaemia (n = 4) (mean age 7 years 2 months), with a greater degree of splenomegaly, lower haemoglobin, and higher white cell counts, platelet counts and bilirubin values (P less than 0.05 for all). Twenty-nine children with HbSS had evidence of poor reticuloendothelial function, with red cell pitting of greater than or equal to 2%. Three of these 29 had low levels of endotoxin in plasma (0.12-0.24 endotoxin units (EU)/ml); two were clinically well, one had a painful crisis. Eight of 18 children with other sickle haemoglobinopathies had greater than or equal to 2% pitted red cells; none was endotoxinaemic. Therefore, in 37 patients with reticuloendothelial dysfunction, three were endotoxinaemic; all had sickle cell anaemia. Although not statistically significant, this suggests that endotoxinaemia may occur predominantly in patients with reticuloendothelial dysfunction, and is compatible with the hypothesis that systemic endotoxinaemia can derive from the intestine especially when reticuloendothelial function is depressed.

Adolescent↗
PubMed1988

Concealed paroxysmal atrioventricular block: diffuse congenital atrioventricular conduction system disorder with nonpropagated His bundle depolarizations.

A 2 1/2-year-old girl with bradycardia and left bundle branch block at birth began to experience "night cries" when deeply asleep. Electrophysiological study demonstrated congenital diffuse atrioventricular conduction disease with concealed paroxysmal atrioventricular block, nonpropagated His bundle depolarizations, severe sinus node abnormality, and a low atrioventricular junctional escape rhythm with probable reciprocation. After pacemaker implant, the "night cries" ceased.

Bradycardia↗
PubMed1988

Repair of interrupted aortic arch in infancy.

Twenty-one patients undergoing repair of interrupted aortic arch between December of 1979 and January of 1987 were reviewed to determine the cause(s) of late morbidity and mortality. Ten underwent staged repair, and 11 had complete repair including all coexisting defects at the initial operation. Sixty-two percent are alive and clinically well 6 months to 6 years after the initial operation. Among the five patients who died late postoperatively, four had severe left ventricular outflow tract obstruction. Two other patients have had surgical relief of severe subaortic stenosis. In addition, significant recurrent or residual coarctation was found in four patients; it was relieved by balloon angioplasty in two patients, and two had surgical repair. None of the most recent seven patients, however, have had a residual ascending-descending aortic gradient. Careful follow-up for the detection of previously masked or newly developed left ventricular outflow tract obstruction is imperative and may be lifesaving.

Aorta, Thoracic↗
PubMed1988

Arterial repair for transposition of the great arteries and large ventricular septal defect in early infancy.

Arterial repair for transposition of the great arteries and large ventricular septal defect (VSD) may be superior to atrial correction, but the risk of either approach in early infancy has been high. The results of early correction were therefore assessed in 12 children with transposition of the great arteries and a large VSD who underwent arterial repair. Patients ranged in age from 3 to 90 days (median age, 19 days) and in weight from 2.5 to 3.7 kg. The VSD was infundibular in eight, inlet in three, and muscular in one. Coronary artery anomalies were present in five patients, including one patient with a single left coronary artery. There was one early death (8%) in the only patient with a pulmonary artery band. There were no late deaths. The 11 survivors have been followed up from 2 to 59 months (mean follow-up period, 20 months) and remain free of cardiac symptoms. Catheterization (n = 5) and Doppler echocardiography in all patients show no significant left ventricular outflow obstruction, aortic insufficiency, or residual VSD. Catheterization documented normal pulmonary artery pressure and unobstructed coronary arteries. Only one patient had significant pulmonary stenosis and underwent successful reoperation. These data indicate that arterial repair and VSD closure can be successfully performed in early infancy with low mortality and morbidity. Repair in this age group is advocated before changes of pulmonary vascular disease occur.

Angiography↗