Transvenous pacing implantation: techniques, tips, and lessons learned along the way.

The right ventricular apex has been the traditional site for lead placement in veterinary patients who require permanent cardiac pacing therapy for atrioventricular block and sick sinus syndrome. Implantation of leads in this location is a straightforward procedure that most veterinary cardiologists perform routinely. Pacing at the right ventricular apex, however, has been demonstrated to have long-term deleterious effects on the left ventricular function in numerous patient populations and animal models. Alternative lead placement sites and pacing system configurations have been developed, and the purpose of this review article is not to review the literature or the decision-making process in selecting a specific pacing system but rather to share the experiences of our group with the use of alternative pacing implantation techniques for veterinary patients in need of permanent cardiac pacing.

Ventricular arrhythmia in the X-linked cardiomyopathy Barth syndrome.

Barth syndrome is an X-linked disorder characterized by dilated cardiomyopathy, cyclic neutropenia, skeletal myopathy, abnormal mitochondria, and growth deficiency. The primary defect is a mutation in the TAZ gene on the X chromosome at Xq28, resulting in abnormal phospholipid biosynthesis and cardiolipin deficiency. To date, there has been no systematic evaluation of the cardiac phenotype. We report five cases of cardiac arrest and/or placement of an internal cardiac defibrillator with documented ventricular arrhythmia. We suggest that ventricular arrhythmia is part of the primary phenotype of the disorder and that patients should be screened accordingly.

KCNQ1 mutations in patients with a family history of lethal cardiac arrhythmias and sudden death.

Long QT syndrome (LQTS) is the prototype of the cardiac ion channelopathies which cause syncope and sudden death. LQT1, due to mutations of KCNQ1 (KVLQT1), is the most common form. This study describes the genotype-phenotype characteristics in 10 families with mutations of KCNQ1, including 5 novel mutations. One hundred and two families with a history of lethal cardiac events, 55 LQTS, 9 Brugada syndrome, 18 idiopathic ventricular fibrillation (IVF), and 20 acquired LQTS, were studied by single-strand conformational polymorphism (SSCP) and DNA sequence analyzes. Families found to have KCNQ1 mutations were phenotyped using ECG parameters and cardiac event history, and genotype-phenotype correlation was performed. No mutations were found in Brugada syndrome, IVF, or acquired LQTS families. Ten out of 55 LQTS families had KCNQ1 mutations and 62 carriers were identified. Mutations included G269S in domain S5; W305X, G314C, Y315C, and D317N in the pore region; A341E and Q357R in domain S6; and 1338insC, G568A and T587M mutations in the C-terminus. W305X, G314C, Q357R, 1338insC, and G568A, appeared to be novel mutations. Gene carriers were 26 +/- 19 years (32 females). Baseline QTc was 0.47 +/- 0.03 s (range 0.40-0.57 s) and 40% had normal to borderline QTc (< or = 0.46 s). Typical LQT1 T wave patterns were present in at least one affected member of each family, and in 73% of all affected members. A history of cardiac events was present in 19/62 (31%), 18 with syncope, 2 with aborted cardiac arrest (ACA) and six with sudden death (SD). Two out of 6 SDs (33%) occurred as the first symptom. No difference in phenotype was evident in pore vs. non-pore mutations. KCNQ1 mutations were limited to LQTS families. All five novel mutations produced a typical LQT1 phenotype. Findings emphasize (1) reduced penetrance of QTc and symptoms, resulting in diagnostic challenges, (2) the problem of sudden death as the first symptom (33% of those who died), and (3) genetic testing is important for identification of gene carriers with reduced penetrance, in order to provide treatment and to prevent lethal cardiac arrhythmias and sudden death.

Hypertrophic cardiomyopathy in children.

Hypertrophic cardiomyopathy is a congenital disease that may be manifested in infancy, childhood, adolescence, or young adulthood. It is heterogeneous both genotypically and phenotypically, and as such, it requires an individualized approach to medical management. The symptomatic patient can have progression of symptoms but can be treated with appropriate medical or surgical therapy. The symptomatic infant usually has a grave prognosis and should be given early consideration for heart transplantation. The future holds promise because genotyping may recognize pedigrees with more "malignant" courses that can be treated more aggressively to prevent sudden death. The greatest challenge lies with the primary care physician who must take careful measures to identify those asymptomatic patients who may be at risk for sudden death during athletic activities.

Left ventricular performance following the arterial switch operation: use of noninvasive wall stress analysis in the postoperative period.

OBJECTIVE: To determine postoperative left ventricular mechanics following the arterial switch operation (ASO). DESIGN: Prospective, cohort study. SETTING: Pediatric cardiac recovery room. PATIENTS: Nine neonates with transposition of the great arteries undergoing the ASO within the first week of life. INTERVENTIONS: Noninvasive ejection phase indices: shortening fraction (% SF), corrected mean velocity of circumferential shortening (VCFc), and wall stress analysis were used to calculate indices of specific left ventricular systolic mechanics. The % SF and VCFc were respectively adjusted for left ventricular afterload (end-systolic wall stress) to derive an index for left ventricular performance (stress-shortening relation) and contractility (stress-velocity relation). Left ventricular preload was assessed as the variance between the performance and contractility indices. All indexed data are reported as mean Zscore (i.e., number of standard deviations from the mean of a normal age- and body surface area-adjusted population). A mean Zscore of < -2 or > 2 was regarded as a significant variance from normal. Transmitral Doppler flow patterns were recorded at each postoperative interval and analyzed for isovolumic relaxation time (IVRT) as an index of left ventricular compliance. MEASUREMENTS AND MAIN RESULTS: All nine patients did well clinically and completed the study. Noninvasive parameters were measured at mean intervals of 3 (early), 23 (intermediate), and 48 hrs (late postoperative) relative to the time of arrival in the cardiac recovery room. Postoperative left ventricular performance was decreased throughout the early (-4.0 +/- 1.5 SD), intermediate (-4.1 +/- 2.8), and late (-3.5 +/- 1.3) phases of recovery. In contrast, the overall left ventricular contractility remained normal throughout the three postoperative intervals (0.2 +/- 1.8, -1.2 +/- 1.9, and -1.0 +/- 1.6, respectively), although three of the nine patients had a diminished stress-velocity index during the study period. Left ventricular afterload was within normal range in the early (0.1 +/- 1.7) and intermediate (1.5 +/- 1.9) phases of recovery, but increased in the late postoperative period (2.5 +/- 2.9). Left ventricular preload was decreased significantly throughout the early (-4.2 +/- 1.3), intermediate (-2.8 +/- 2.0), and late (-2.5 +/- 1.0) postoperative phases. All nine patients demonstrated decreased preload during the recovery period. IVRT was decreased in the post-ASO patients at each phase of recovery compared with normal data (p < .001). CONCLUSIONS: Left ventricular performance is impaired in infants during the period immediately following the ASO. A persistent preload deficit closely matches the pattern of impaired ventricular performance. Decreased IVRT points to impaired ventricular compliance as the etiology of the altered preload. In contrast, left ventricular contractility remains normal in the majority of post-ASO patients. Decreased contractility may account for impaired ventricular performance in selected cases.

Cisapride-induced long QT interval.

A 2-month-old infant with gastroesophageal reflux was treated with cisapride. Bradycardia developed and an electrocardiogram revealed 2:1 atrioventricular conduction and a prolonged QT interval. After cessation of cisapride therapy, both the rhythm and the QT interval returned to normal. Prolonged QT interval during treatment with cisapride may occur in children as in adults.

Variability in three morphologic features of the permanent maxillary central incisor.

Variability in tooth morphology can play a significant role in appliance design and the achievable results of orthodontic treatment. This investigation was undertaken to determine quantitatively the variation in three anatomic features of the maxillary central incisor. The three features are the crown-root angulation in a labiolingual direction, the angle formed by a tangent to the middle of the labial surface of the crown and the long axis of the crown from a proximal view, and the lingual curvature of the crown from a proximal view. Tracings of maxillary central incisors were made from two different sources. The first source consisted of radiograms of 98 extracted central incisors, and the second source was a group of 100 cephalometric radiograms which were part of pretreatment records of patients in the Orthodontic Department. The cephalometric radiograms included 25 Angle Class I, 25 Class II, Division 1, 25 Class II, Division 2, and 25 Class III malocclusions. The first measurement taken was the angle formed by the long axis of the crown and the long axis of the root. The second measurement was the angle formed by the long axis of the crown and a tangent to the midpoint of the labial surface of the crown. For the third measurement, the lingual curvature of the crown was described by a mathematical equation whose parameters were used for comparisons. The results revealed a wide range of variation in the three features measured. The mean crown-root angle for Class II, Division 2 malocclusions differed significantly from that for Class II, Division 1 and Class III malocclusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Antinociceptive actions of morphine and buprenorphine given intrathecally in the conscious rat.

1 The antinociceptive effects of morphine and buprenorphine given intrathecally and subcutaneously have been compared in the conscious rat. 2 In the paw pressure test, when given subcutaneously buprenorphine 0.001-0.1 mg/kg s.c., was approximately 100 times more potent than morphine 0.1-3 mg/kg s.c., but in the hot plate test, buprenorphine 0.03-3.0 mg/kg s.c., produced a bell-shaped dose-response curve of low maximum effect and was about equipotent with morphine 0.03-3 mg/kg s.c. 3 When given intrathecally buprenorphine 10 micrograms and morphine, 10-60 micrograms, were approximately equipotent in both paw pressure and hot plate tests. Furthermore, morphine produced these effects at 1/25th of the minimum effective parenteral dose while the dose of buprenorphine exceeded the parenteral dose. 4 It is concluded that the predominant site of the analgesic action of buprenorphine is supraspinal. The significance of these findings in relation to the role of spinal opiate receptors is discussed.

Involvement of the median raphe nucleus in antinociception induced by morphine, buprenorphine and tilidine in the rat.

1 Antinociception induced by three analgesics with differing profiles of activity, morphine, buprenorphine and tilidine, have been evaluated in the hot plate and paw pressure tests after administration by the subcutaneous route and directly into the median raphe nucleus in the conscious rat. 2 Behavioural and neurological effects of the three analgesics were also assessed. 3 The typical profiles of antinociceptive activity induced by the three analgesics were qualitatively similar after either route of administration. Morphine induced naloxone-sensitive dose-dependent effects in both tests. Buprenorphine showed naloxone-sensitive effects with a bell-shaped dose-response curve in the thermal test but dose-dependent activity in the pressure test. Tilidine induced naloxone-sensitive dose-dependent effects in the thermal test but demonstrated naloxone-insensitive activity in the paw pressure test. 4 The behavioural and neurological effects of the analgesics in the dose range used would not have affected the animals' ability to respond to the nociceptive stimuli. 5 The results suggest that the median raphe could participate in drug-induced antinociception. The mechanisms by which this might occur are discussed.