Radiofrequency ablation of macro re-entrant arrhythmias: cure or adjunctive therapy?
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Atrial Flutter↗
Biomedical subjects
M D Gammage
Publications and source records attributed to M D Gammage.
Experience with a lead fixation/suture sleeve.
Current anchoring systems on pacemaker leads are crude in comparison to the lead technology. Poor anchoring technique may cause damage to the lead or early displacement from incorrect suture tension. We describe experience with a locking anchoring sleeve that applies a constant gripping force to the lead body. This can be locked and unlocked to allow optimal positioning after fixation of the sleeve to underlying tissues. The sleeve was fitted to a 55D polyurethane lead (Medtronic 4024, 7 Fr, bipolar, steroid eluting) implanted in the ventricular position in 22 patients at four European centers. All implants were uncomplicated; data were collected on handling and ease of use. Assessments were made using a scale of 1-10 (10 = excellent, 5 = equivalent to conventional sleeve). Overall ease of use compared to conventional sleeve was 7.79 +/- 0.62 (mean +/- SD). Mean scoring of flexibility of the lead at the transition points was 7.92 +/- 0.72; ability to lock/unlock the sleeve scored 6.28 +/- 1.78. Ease of suturing around the sleeve scored 8.07 +/- 0.77, and ability to slide the sleeve along the lead body scored 6.48 +/- 1.99. Chest X rays at 6 weeks showed no change in lead position with respect to postimplant films, and all leads showed a straight path on either side of the sleeve with no evidence of conductor distortion. Follow-up to 3 years has been without problem. All leads remain intact and in place, with stable thresholds and no evidence of erosion. There have been no complaints of patient discomfort. We conclude that this device is safe and effective and offers a significant advance in lead fixation.
Defibrillators, Implantable↗
Technical aspects of the CPI Vigor DR device.
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Algorithms↗
AAI pacing for sick sinus syndrome: first choice on all counts.
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Cardiac Pacing, Artificial↗
Transfection of cardiac muscle: effects of overexpression of c-myc and c-fos proto-oncogene proteins in primary cultures of neonatal rat cardiac myocytes.
1. Studies of cells transfected with specific expression vectors allow functions of specific gene products to be investigated. We first established optimum conditions for transfection of neonatal cardiac myocytes in primary culture. Increased proto-oncogene expression has been implicated in the development of cardiac hypertrophy; we therefore wished to examine the effects of overexpression of the c-myc and c-fos proto-oncogenes induced by cell transfection on cell growth. 2. Neonatal rat ventricular myocytes were transfected by electroporation, voltage and capacitance settings were optimized and these conditions were then used to transfect expression vectors encoding MYC and FOS proteins into this cell type. Effects on cell number, DNA synthesis and protein content were determined. 3. Increased expression of c-myc and c-fos in cells transfected with proto-oncogene expression vectors was confirmed by Northern and Western blotting. Increases in cardiac myocyte cell number, DNA synthesis and total cellular protein were observed in cells transfected with either c-myc or c-fos expression vectors compared with cells transfected with non-coding vectors. 4. Overexpression of MYC and FOS proteins results in hyperplastic rather than hypertrophic growth of the neonatal rat heart, providing evidence for a role of these proteins in the control of myocardial growth.
Animals↗
Tilt testing: a useful screen for rate-drop response.
Tilt testing is accepted as the main tool for the diagnosis of neurocardiogenic syncope, particularly in the "malignant" vasovagal form. As a result of experience with tilt testing, the cardiovascular responses to head-up tilting in patients with malignant vasovagal syncope (MVVS) have been defined in respect of the vasodepressor (hypotensive) and cardioinhibitory (bradycardic) components. Pacing therapy has been of limited value in the past, with controversy about its role, even in the cardioinhibitory form of MVVS. With the advent of more sophisticated algorithms for pacing (i.e., rate-drop response [RDR], Thera DR) in response to the onset of bradycardia in MVVS, however, this therapy is being reexamined. This article examines the blood pressure and heart rate responses to head-up tilt in patients with MVVS and examines the role of this test in screening such patients for the benefits of pacing with RDR. Careful analysis of the pattern of blood pressure and heart rate response during the tilt test may allow selection of those patients likely to respond to RDR and may provide useful information for initial programming of the algorithm.
Algorithms↗
Clinical experience with Thera DR rate-drop response pacing algorithm in carotid sinus syndrome and vasovagal syncope. The International Rate-Drop Investigators Group.
This study examined the effectiveness of cardiac pacing using the Thera DR rate-drop response algorithm for prevention of recurrent symptoms in patients with carotid sinus syndrome (CSS) or vasovagal syncope. The algorithm comprises both diagnostic and treatment elements. The diagnostic element consists of a programmable "window" used to identify heart rate changes compatible with an evolving neurally mediated syncopal episode. The treatment arm consists of pacing at a selectable rate and for a programmable duration. Forty-three patients (mean age 53 +/- 20.4 years) with CSS alone (n = 8), CSS in conjunction with vasovagal syncope (n = 4), or vasovagal syncope alone (n = 31) were included. Thirty-nine had recurrent syncope, while the remaining four reported multiple presyncopal events. Prior to pacing, 40 +/- 152 syncopal episodes (range from 1 to approximately 1,000 syncopal events) over the preceding 56 +/- 84.5 months. Postpacing follow-up duration was 204 +/- 172 days. Three patients have been lost to follow-up and in one patient the algorithm was disabled. Among the remaining 39 individuals, 31 (80%) indicated absence or diminished frequency of symptoms, or less severe symptoms. Twenty-three patients (23/29, or 59%) were asymptomatic with respect to syncope or presyncope. Sixteen patients had symptom recurrences. Of these, seven experienced syncope (7/39, or 18%) and 9 (29%) had presyncope: the majority of patients with recurrences (6/7 syncope and 7/9 presyncope) were individuals with a history of vasovagal syncope. Consequently, although symptoms were observed during postpacing follow-up, they appeared to be of reduced frequency and severity. Thus, our findings suggest that a transient period of high rate pacing triggered by the Thera DR rate-drop response algorithm was beneficial in a large proportion of highly symptomatic patients with CSS or vasovagal syncope.
Adolescent↗
Rate-drop response programming.
Effective programming of the rate-drop response algorithm requires careful attention to the heart rate and blood pressure responses seen during diagnostic tilt testing. In order to undertake effective programming, additional tilt testing procedures may be necessary, and it is vital that the protocol should be identical on each occasion and very careful note taken of exact times of onset of symptoms and relative timing of onset of changes in heart rate and blood pressure. The algorithm settings in the Thera DR generator as delivered (factory or "shelf" parameter settings) must be considered nontherapeutic (an unusual situation for a pacemaker algorithm) and will require adjustment for each individual patient. Effective therapeutic settings are likely to result in an excess of pacing interventions; these, however, tend to be less symptomatic than the syncope or presyncope suffered by the patient and are generally well tolerated or not noticed.
Algorithms↗
A synopsis: neurocardiogenic syncope, an international symposium, 1996.
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Age Factors↗
The increasing use of mode-switching.
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Artifacts↗
Investigation of low density lipoprotein subfractions as a coronary risk factor in normotriglyceridaemic men.
There is an increasing interest in low density lipoprotein (LDL) subfractions since some of them are associated with a higher risk for coronary artery disease (CAD). Small LDL particles are particularly atherogenic and more of those are produced in hypertriglyceridaemia. However, high triglyceride concentrations are not the only explanation for the predominance of small LDL particles and other influences, including genetic factors, are also responsible for LDL particle size. We investigated LDL subfraction profiles in two groups: 46 men with and 21 men without CAD proven angiographically. For the separation of LDL subfractions, we used continuous disc polyacrylamide gel electrophoresis (PAGE) that is rapid and easier to perform than the other methods usually used which, although more precise in terms of measuring particle diameter, are much more demanding of time and equipment. The described method is suitable for routine use in assessing large numbers of patients. All studied men had triglyceride concentrations below 2.3 mmol/l. LDL scores were calculated on the basis of all LDL subfractions present in a particular profile; the higher the score, the greater the proportion of small LDL particles. LDL cholesterol (P < 0.05) and LDL score (P < 0.001) were the only significant discriminators between two groups. LDL score was significantly correlated with CAD, even after adjusting for triglyceride and HDL cholesterol concentrations and it was the best discriminant factor for the presence of CAD.
Coronary Disease↗
Idiopathic dysautonomia treated with intravenous gammaglobulin.
BACKGROUND: A previously healthy 23-year-old man presented with a short history of abdominal pain and diarrhoea followed by blurred vision, severe postural hypotension, reduced sweating and unremitting fever. METHODS: Examination revealed fixed dilated pupils, impaired sweating and postural hypotension. Clinical and neurophysiological examination showed no motor or sensory deficit. A diagnosis of idiopathic autonomic neuropathy was made. He became gravely ill with profound life-threatening hypotension and a prolonged ileus. FINDINGS: Within 36 h of receiving intravenous gammaglobulin (IVGG) his pupillary areflexia and severe hypotension resolved. 2 weeks later the autonomic failure recurred but again responded to treatment with IVGG. IVGG is a recognised treatment for Guillain-Barré syndrome. INTERPRETATION: This case report demonstrates that IVGG is also effective in the rare pure dysautonomic variant.
Adult↗
Cardiac hypertrophy as a result of long-term thyroxine therapy and thyrotoxicosis.
OBJECTIVES: To define the effects of long-term thyroxine treatment upon heart rate, blood pressure, left ventricular systolic function, and left ventricular size, as well as indices of autonomic function, and to compare findings with those in patients with thyrotoxicosis before and during treatment. DESIGN: Cross sectional study of patients prescribed thyroxine long term (n = 11), patients with thyrotoxicosis studied at presentation (n = 23), compared with controls (n = 25); longitudinal study of patients with thyrotoxicosis studied at presentation and serially after beginning antithyroid drug treatment (n = 23). METHODS: 24 h ambulatory monitoring of pulse and blood pressure, echocardiography, forearm plethysmography, and autonomic function tests. RESULTS: Long-term thyroxine treatment in doses that reduced serum thyrotrophin to below normal had no effect on blood pressure, heart rate, left ventricular systolic function or stroke volume index, but was associated with an 18.4% increase in left ventricular mass index (mean (SEM) 101.9 (3.09) g/m2 v controls 86.1 (4.61), P < 0.01). Thryoxine treatment, like thyrotoxicosis, had no effect on tests of autonomic function. Untreated thyrotoxicosis resulted in pronounced changes in systolic and diastolic blood pressure and an increase in heart rate during waking and sleep. Patients with thyrotoxicosis at presentation had an increase in left ventricular systolic function (ejection fraction 70.5 (1.66)% v 65.4 (1.79), P < 0.01; fractional shortening 40.4 (1.54)% v 35.6 (1.46), P < 0.01), increased stroke volume index (45.9 (2.4) ml/m2 v 36.6 (1.7), P < 0.001), and an increase in forearm blood flow, and decrease in vascular resistance. They had a similar degree of left ventricular hypertrophy to that associated with thyroxine treatment (99.3 (4.03) g/m2); all changes were corrected within 2 months by antithyroid drugs. CONCLUSIONS: The development of left ventricular hypertrophy in patients receiving thyroxine in the absence of significant changes in heart rate, blood pressure, and left ventricular systolic function is consistent with a direct trophic effect of thyroid hormone on the myocardium. The presence of left ventricular hypertrophy determines that further studies are essential to assess cardiovascular risk in patients taking thyroxine long term.
Adult↗
Cardiovascular function and glucocorticoid replacement in patients with hypopituitarism.
OBJECTIVE: Retrospective analysis suggests an increased mortality from cardiovascular disease in hypopituitary adults; GH deficiency has been postulated to account for this. However, glucocorticoid replacement doses of 30 mg/day of hydrocortisone (HC) may be excessive, and could therefore be implicated in the increased cardiovascular mortality in this group of patients. The aims of this study were to establish whether patients with hypopituitarism have any abnormalities of the cardiovascular system compared to a control group and whether any of these parameters might be improved by reducing the replacement dose of glucocorticoid. PATIENTS AND MEASUREMENTS: A prospective analysis of cardiovascular function was carried out in 13 patients with hypopituitarism on routine replacement therapy and 20 normal controls who were matched for age and body mass index (BMI). Twenty-four-hour ambulatory blood pressure (BP), erect and supine BP, echocardiography, forearm plethysmography and cardiovascular reflexes in response to tilt, Valsalva and isometric hand grip were performed on controls and on patients taking 30 mg/day of HC and repeated following a reduction in HC dose to 15 mg/day for 3 months. Weight, plasma and urinary electrolytes, 24-hour urinary cortisol excretion, glucose, HbA1C and pituitary function were also assessed on HC 30 mg/day and 15 mg/day. RESULTS: Mean 24-hour ambulatory BP, in addition to day and night time BP, was lower in patients than in controls (achieving statistical significance in the male subgroup) and did not change significantly with a reduction in HC dose. Erect and supine BP was also lower in patients compared to controls and there was no evidence of postural hypotension following a reduction in HC dose to 15 mg/day. Systolic and diastolic left ventricular dimensions, interventricular septal thickness, ejection fraction and fractional shortening were similar in controls and patients and did not alter with a reduction in HC dose. Systolic and diastolic BP and heart rate responded appropriately to all tests of cardiovascular reflexes (tilt, Valsalva and isometric handgrip) in hypopituitary patients though again measurements of systolic BP were significantly lower in patients during these tests, independent of HC dose. Forearm plethysmography was similar in patients receiving 30 mg of HC and controls but forearm blood flow increased significantly when the HC dose was reduced to 15 mg/day. There was no change in weight, plasma and urinary electrolytes, glucose and HbA1C or pituitary function in the patient group throughout the study. CONCLUSIONS: In contrast to other studies we have failed to confirm cardiovascular dysfunction in GH deficient hypopituitary adults. Indeed, cardiovascular protection may be conferred on this group by the lower BP levels. Although a reduction in hydrocortisone dose was well tolerated in all patients, it appeared to confer no additional clinical benefit over the 3-month study period. In view of the conflicting data on cardiovascular function in hypopituitary patients, further prospective mortality studies are required in patients with adult GH deficiency.
Adult↗
Comparison of externally strapped versus implanted accelerometer- or vibration-based rate adaptive pacemakers during various physical activities.
The ability of externally strapped accelerometer- (Excel [Cardiac Pacemakers, Inc.]) and vibration-based (Activitrax [Medtronic, Inc.]) rate adaptive pacemakers to reproduce the rate response of the same implanted devices with identical programming was evaluated in ten patients by ambulatory Holter monitoring. The resting and postexercise external pacemaker rates closely resembled those of the respective implanted devices. During short bursts and more prolonged exercise, both types of strapped-on devices underestimated maximal implanted pacemaker rate response by 4%-10% when programmed to nominal rate adaptive settings. Studies evaluating chronotropic responses from either type of externally strapped activity sensor appear valid, provided the modest attenuation in maximal rate increase by this method is appreciated.
Aged↗
Comparison of sinus node response to exercise with responses from two different activity-based rate adaptive pacemakers in healthy subjects of different age groups.
The pacing rates from accelerometer-based (Excel) and piezoelectric-based (Legend) activity sensing rate adaptive pacemakers, both strapped externally in the pectoral position, were compared with sinus rate response in normal volunteers of two different age groups (group 1, mean age 35 +/- 16 years; group 2, mean age 72 +/- 9 years) during various physical activities. Both pacemakers were programmed in manufacturers' nominal rate adaptive settings. Both types of activity sensing pacemakers programmed in this way showed chronotropic deficiencies to metabolic demand in healthy young subjects and in those matching the usual age of pacemaker implant, especially during "burst" activities. These data suggest that present recommended activity sensing rate response algorithms for accelerometer and piezoelectric pacemakers are inappropriate for many physical activities.
Adult↗
Hypertension and the heart.
The heart is of great importance in systemic hypertension; it has a role in its pathogenesis but also suffers its consequences. Heart disease is, therefore, often found in hypertensive patients. Patients with hypertension may develop left ventricular hypertrophy, cardiac failure and atherosclerotic vascular problems, such as coronary artery disease, as well as strokes and peripheral vascular disease. There have been a great many advances in our understanding of the pathogenesis of hypertensive heart disease as well as its epidemiology over the last decade and these are reviewed briefly here.
Antihypertensive Agents↗