Radiofrequency catheter ablation of atrial tachycardia

BACKGROUND

Atrial tachycardia is a relatively uncommon arrhythmia which usually responds poorly to antiarrhythmic drug therapy. Transcatheter radiofrequency (RF) ablation is a new therapeutic modality for patients with atrial tachycardia.

AIM

This study analyses our early experience with the treatment of atrial tachycardia by this technique.

METHODS

Thirteen consecutive patients (age 13-63 years) with 15 drug-refractory atrial tachycardia foci were treated with RF catheter ablation. Atrial tachycardia was mapped by seeking the earliest atrial activation in the right atrium in eight patients and in the left atrium in five.

RESULTS

Tachycardias were abolished in nine (69%) patients, including two sinoatrial re-entrant tachycardias and seven automatic atrial tachycardias, after 9 +/- 10 (range, one to 28) pulses of RF current. Six of these ablated atrial tachycardia foci were right sided and three were on the left. One patient had three separate right atrial tachycardia foci; one was eliminated. Tachycardia recurred after two weeks in one patient with apparently successful ablation of sinoatrial re-entrant tachycardia. One patient with successful ablation of a right atrial tachycardia developed cardiac tamponade requiring surgical intervention.

CONCLUSION

This study demonstrates that atrial tachycardia arising from diverse sites can be eliminated by RF catheter ablation.

Role of nitric oxide in the coronary microvascular responses to adenosine and increased metabolic demand

BACKGROUND

The purpose of this study was to test the hypothesis that endothelium-derived nitric oxide (NO) participates in coronary microvascular responses to adenosine and pacing-induced increases in metabolic demand by maintaining an optimal distribution of coronary resistance.

METHODS AND RESULTS

Coronary microvascular diameters were measured by stroboscopic epi-illumination and intravital microscopy in open-chest dogs (n = 20). Epicardial coronary blood velocity (CBV) was measured by Doppler flowmetry. Responses to adenosine (1 and 10 micrograms.kg-1.min-1 IC) and left atrial pacing (180 beats per minute) were recorded before and after inhibition of NO synthesis by NG-nitro-L-arginine methyl ester (L-NAME, 30 micrograms.kg-1.min-1 IC). At baseline, adenosine dilated arterioles (< 100 microns) (11 +/- 4% and 25 +/- 3% diameter changes, P < .05) more than small arteries (> 100 microns) (-4 +/- 6% and 7 +/- 3%, P < .05 for the higher dose) and increased CBV (43 +/- 31% and 118 +/- 25%, P < .05). Left atrial pacing dilated arterioles (12 +/- 2%, P < .05) and small arteries (8 +/- 3%, P < .05) and also increased CBV (68 +/- 9%, P < .05). L-NAME abolished CBV increases caused by acetylcholine (10 and 100 ng.kg-1.min-1 IC; 53 +/- 33% and 168 +/- 82% versus -12 +/- 15% and -1 +/- 14%, P < .05) but not papaverine. Small arteries were constricted by L-NAME (-8 +/- 2%, P < .05), arterioles were dilated (10 +/- 4%, P < .05), and CBV was unchanged. After L-NAME, adenosine failed to dilate arterioles further (3 +/- 3% and 2 +/- 2%; P < .05 versus prior responses), and CBV changes were attenuated (14 +/- 16% and 8 +/- 13%; P < .05 versus prior responses). Pacing also failed to dilate arterioles (-4 +/- 2%, P < .05 versus prior response), resulting in an attenuated CBV change (34 +/- 13%, P < .05 versus prior response). The possibility that adenosine stimulates NO release in canine coronary arterioles was investigated in isolated arterioles (diameters, 81 +/- 4 microns; n = 8). Adenosine caused dose-dependent dilation to maximal diameter, which was unaffected by inhibition of NO synthesis by L-NAME.

CONCLUSIONS

Inhibition of NO synthesis attenuates coronary dilation during adenosine infusions and during pacing-induced increases in metabolic demand. Inhibition of NO synthesis may shift the major site of coronary resistance into small arteries through autoregulatory adjustments in arterioles. These data therefore suggest that NO, by dilating predominantly small coronary arteries, promotes metabolic coronary dilation by preserving the tone and vasodilator reserve of arterioles.

Substance P-induced calcium entry in endothelial cells is secondary to depletion of intracellular stores

Substance P (SP) induces an elevation in cytosolic Ca2+ concentration ([Ca2+]i) in porcine coronary artery endothelial cells by way of Ca2+ influx and release from intracellular stores. We tested the hypothesis that SP-induced Ca2+ influx occurs due to activation of a Ca(2+)-permeable influx pathway coupled to depletion of intracellular stores. With the use of the perforated patch technique and fura 2 microfluorimetry, a fivefold greater increase in [Ca2+]i per unit decrease in membrane potential was obtained in the presence of SP (10 nM) compared with resting state, implying that SP increased Ca2+ conductance. When K+ channels were blocked, SP activated a net inward current with a reversal potential (2.5 +/- 1 mV) not significantly different from that (2 +/- 1 mV) for inward current recorded in response to store depletion by (2,5-di-tert-butylhydroquinone) (BHQ, 10 microM). Increasing bath [Ca2+] induced a similar shift in reversal potential for SP- and BHQ-induced currents. Inositol 1,4,5-trisphosphate (20 microM), applied through the patch pipette, activated an inward current with Ca2+ selectivity similar to SP- and BHQ-activated currents. Dialysis of cells with heparin (5 mg/ml) completely blocked SP-induced inward current but not BHQ-induced current. These results suggest that the SP-induced increase in Ca2+ conductance can be completely explained by activation of a Ca(2+)-permeable influx pathway coupled to depletion of intracellular stores.

Neurological assessment of the child with head trauma

Dental trauma is a type of head trauma. It is essential that the dentist be able to assess the gross neurological status of the child presenting with head injury and to recognize acute and delayed signs of nerve injury. Time does not permit the dentist a leisurely review of necessary skills at the time of an emergency visit. He or she must be prepared in advance with a consistent and simple approach for the management of head trauma in children. Time of entry into care is critical to the prognosis.

Day stay transcatheter radiofrequency ablation for supraventricular tachyarrhythmias

OBJECTIVE

To describe our initial experience with transcatheter radiofrequency ablation as a day stay procedure for patients with supraventricular tachyarrhythmias resulting from aberrant atrioventricular pathways.

DESIGN

Prospective study of the first 50 patients at the Royal Perth Hospital whom we intended to treat and discharge on the same day. Patients underwent a combined electrophysiological study and radiofrequency ablation.

RESULTS

Accessory pathways were identified in 32 patients (successfully ablated in 30) and dual atrioventricular nodal pathways in 18 patients (with successful ablation of the slow pathway in 17). Thirty-eight patients were discharged on the same day (24 treated for accessory pathways, and 14 treated for dual atrioventricular nodal pathways). There were no late complications or readmissions in patients discharged on the same day.

CONCLUSIONS

In patients with supraventricular tachyarrhythmia, day stay transcatheter ablation can be planned without a definitive prior diagnosis of the physiological cause. Complications or other reasons for overnight admission are apparent at completion of the procedure.

Combined ultrasound and fluorescence spectroscopy for physico-chemical imaging of atherosclerosis

This paper describes a combined ultrasonic and spectroscopic system for remotely obtaining physico-chemical images of normal arterial tissue and atherosclerotic plaque. Despite variations in detector-tissue separation, R, fluorescence powers corresponding to pixels in the image are converted to the same set of calibrated units using distance estimations from A-mode ultrasound reflection times. An empirical model, validated by Monte Carlo simulations of light propagation in tissue, is used to describe changes in fluorescence power as a function of R. Fluorescence spectra of normal and atherosclerotic human aorta obtained with this system are presented as a function of R. To compensate for changes in fluorescence power with R, the empirical model was used in each case to calculate the fluorescence power at a constant reference value of R(Rref = 1.67 mm). Prior to compensation, tissue fluorescence power decreased more than a factor of two as R was increased from 2.5 to 5 mm. Following compensation, the fluorescence power varied less than +/- 10% of the average compensated peak. The chemical composition of each sample was determined by fitting its fluorescence spectrum (in calibrated units) to a model of tissue fluorescence incorporating structural protein and ceroid fluorescence, as well as structural protein and hemoglobin attenuation. Parameters of the fit were used to classify tissue type. Without compensation for distance variation, classification of tissue type was frequently incorrect; however, with compensation, predictive value was high. A 1-D chemical image of a section of human aorta containing both normal and atherosclerotic regions obtained with this system is also presented. After compensation for detector-sample separation, tissue classifications along the cross-section closely resemble those obtained from histology. Regions of elevated ceroid concentration and intimal thickening are clearly observable in the resultant chemical image. The potential value of this type of system in the diagnosis and treatment of coronary artery disease is discussed.

alpha-adrenergic responses of isolated canine coronary microvessels

Although alpha-adrenergic activation is known to increase coronary microvascular resistance in vivo, the magnitude of its segmental microvascular consequences is not well understood. Quantification of these effects in vivo is hindered by escape mechanisms that minimize the influences of constrictors, and alterations in flow and pressure, which effect microvascular tone by shear stress-dependent and myogenic mechanisms, respectively. To eliminate these confounding influences, we have studied responses in vitro under conditions with these variables controlled. We evaluated the diameter changes of isolated canine coronary arterioles (110 +/- 12 microns, n = 35) response to alpha-adrenergic activation by norepinephrine (10(-10) to 10(-4) M) in the presence of beta-adrenergic blockade by alprenolol (10(-6) M). In contrast to the situation in vivo, alpha-adrenergic activation did not constrict isolated coronary arterioles, but constricted isolated coronary venules in a dose-dependent manner over a range of 10(-10) to 10(-4) M (-27 +/- 3% maximum diameter change). Coronary arteriolar alpha-adrenergic constriction was not promoted by 1) subthreshold or vasoactive doses of the vasoconstrictors KCl, angiotensin II, U46619, endothelin-1, neuropeptide Y or arginine vasopressin, 2) inhibition of the presynaptic uptake of norepinephrine by imipramine (10(-6) M), 3) inhibition of EDRF synthesis by NG-monomethyl-L-arginine (10(-5) M) or 4) inhibition of prostaglandin synthesis by indomethacin (10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Chloride and cation currents activated by bradykinin in coronary venular endothelial cells

Bradykinin (BK) is known to activate several types of ion channels in endothelial cells, including a K+ channel and a nonselective cation channel. The predominant BK-activated current in most endothelial cells appears to be an outward, Ca(2+)-activated K+ current. We consistently recorded a rapidly activated, spontaneously inactivated inward current stimulated by BK in bovine coronary venular endothelial cells (CVECs). With the use of a whole cell, perforated patch recording mode, the average magnitude of the current was -293 +/- 38 pA. Simultaneous measurements of current and intracellular Ca2+ concentration ([Ca2+]i) showed that the inward current correlated closely with transient increases in [Ca2+]i due to Ca2+ release from intracellular stores. The current could be blocked by 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS) but not by La3+, and it persisted in Ca(2+)-free/Na(+)-free solution. When intra- and/or extracellular Cl- concentrations were altered, the reversal potential of the current shifted according to the calculated Cl- -equilibrium potential, indicating that the current was carried primarily by Cl-. Another inward current was also activated by BK. This current was slower to activate, could be blocked by La3+, but was not blocked by DIDS. The time course of the slowly activated current correlated with the plateau phase of the BK-stimulated [Ca2+]i increase, which was similar to the behavior of a nonselective cation current reported previously. We propose that these two currents may contribute to the depolarizations and net inward currents induced by BK in this cell line.

Measurement of hand bone mineral content by dual energy x-ray absorptiometry: development of the method, and its application in normal volunteers and in patients with rheumatoid arthritis

OBJECTIVES--To develop a method of measuring hand bone mineral content (BMC) by dual energy x ray absorptiometry (DXA); to apply this method of measuring hand BMC to normal volunteers to ascertain causes of variability; and to measure hand BMC in patients with rheumatoid arthritis (RA) of varying duration and severity. METHODS--The x ray beam of the Hologic QDR 1000 dual energy x ray absorptiometer was hardened by introducing a perspex-aluminium plate and the analysis software altered to allow for the small tissue bulk of the hand compared with the torso. Ninety five volunteers (46 men age 24-81 and 49 women age 20-83) had scans of both hands. Eight volunteers were assessed repeatedly to establish reproducibility and effect of hand position. Fifty six patients (22 men, 34 women, age range 25-86 years) with RA of differing duration and severity, had hand BMC measurement by DXA. RESULTS--The precision of BMC measurement was 2.3% with no additional variation due to hand position. Hand dominance had no significant effect on BMC. In men, hand BMC correlated with height (r = 0.57, p < 0.0001), weight (r = 0.58, p < 0.0001), forearm span (r = 0.5, p = 0.0006) and hand volume (r = 0.66, p < 0.0001). In women hand BMC correlated with height (r = 0.66, p < 0.0001), weight (r = 0.4, p = 0.003), forearm span (r = 0.3, p = 0.03) and hand volume (r = 0.49, p = 0.0008). After correcting for all these variables, male volunteers had significantly higher hand BMC than female volunteers (p = 0.01) and patients with RA had lower hand BMC than normal volunteers (total hand BMC in male volunteers 90.9 gms, 95% CI 86.9-95, in male patients 81.7 gms, 95% CI 73.7-89.6, p < 0.004, total hand BMC in female volunteers 62.2 gms 95% CI 59.8-64.5, female patients 52.3 gms, 95% CI 48.1-56.5, p < 0.005). In patients with RA, the hand BMC showed an inverse correlation with age (r = -0.44, p = 0.01), disease duration (r = -0.62, p = 0.0003), Larsen's grades (r = -0.62, p = 0.0002) and modified Sharp's method score (r = -0.69, p < 0.0001) in female patients only. CONCLUSIONS--A new, sensitive and reproducible technique of measurement of hand bone mineral content by DXA, has been developed and this method has been applied to normal volunteers and patients with RA. Hand dominance had no significant effect on hand BMC. After correcting for physical size, men have higher hand BMC than women. Hand BMC inversely correlates in women patients with disease duration and other validated methods of assessing radiological outcome in RA. Longitudinal studies are needed to establish its role in monitoring disease progression.

Combination therapy for rheumatoid arthritis and drug-induced systemic lupus erythematosus

Development of drug-induced systemic lupus erythematosus (SLE) is an uncommon complication of the use of D-penicillamine and sulphasalazine. We report two cases of patients with rheumatoid arthritis (RA) who developed symptoms and signs of SLE and suggest that increasing use of these two agents as combination therapy in RA may cause an additive risk to the occurrence of this complication.

Predictors of early and late recurrence of atrioventricular accessory pathway conduction after apparently successful radiofrequency catheter ablation

The correlation between electrophysiologic parameters and recurrence in 239 patients who underwent successful catheter ablation for an accessory pathway mediated tachycardia was analysed. Pathway conduction recurred in 15 patients (6.3%) after a mean follow-up of 7.3 months. Recurrence was most common in patients with right free wall pathways (17.1%). Accessory pathway conduction resumed in 18.9% of patients with decremental ventriculo-atrial (VA) conduction post-ablation compared with those patients without VA conduction (3.4%) (P < 0.001). Recurrence was common also in patients with repeated return of accessory pathway conduction during the ablation procedure (40% vs. 1.3%, P < 0.01). The patients in whom these observations are made should be monitored closely for recurrence of accessory pathway conduction post-ablation.

Whole-cell and single-channel calcium currents in guinea pig basal forebrain neurons

1. Whole-cell and single-channel patch-clamp recordings of calcium (Ca2+) currents were made in acutely dissociated neurons from the medial septum (MS) and nucleus of the diagonal band (nDB) of adult guinea pig. Barium (Ba2+) was used as the charge carrier across the Ca2+ channel and multiple channel types were identified in different cell types. 2. Both low-voltage-activated (LVA) and high-voltage-activated (HVA) currents were distinguished on the basis of steady-state voltage dependence, activation and inactivation properties, and pharmacological sensitivity. HVA currents had activation thresholds approximately 20 mV more positive than LVA currents. Steady-state inactivation of HVA currents was approximately 50% when the holding potential was shifted from -80 to -40 mV. 3. The dihydropyridines had consistent effects on HVA currents. The amplitude was increased and the activation threshold shifted by 10 mV in the hyperpolarizing direction in the presence of the agonist Bay K 8644 (2-5 microM). The antagonist nifedipine (10 microM) produced approximately 50% inhibition of HVA currents from a holding potential of -80 mV. 4. A second component of the HVA current was blocked by omega-conotoxin (omega-CTX) (300-700 nM). At a holding potential of -80 mV, omega-CTX inhibited 45% of the HVA current. 5. LVA currents were activated near -70 mV and displayed time-dependent inactivation during a 200- to 300-ms voltage step. Voltage-dependent inactivation of LVA currents was also observed and could be described by a single Boltzman relationship with a half-inactivation potential of -84 mV. LVA currents were not significantly changed by Bay K 8644 and were not blocked by low concentrations of nifedipine or omega-CTX. 6. Single voltage-gated Ca2+ channels were investigated using cell-attached patches. In these experiments, 100 mM Ba2+ was used in the patch pipette and the membrane potential was zeroed with isotonic potassium (K+)-aspartate. A low-conductance channel was activated at negative potentials and inactivated rapidly during a 200- to 300-ms voltage step. Unitary amplitudes were determined at different membrane potentials with single-channel conductances calculated to be 7.8 +/- 1.2 (SD) pS. These channels were not blocked by nifedipine (10 microM) and appeared similar to T channels previously reported in both peripheral and central neurons. Ensemble averages from cell-attached patches of T channels resembled LVA currents recorded in the whole-cell configuration.(ABSTRACT TRUNCATED AT 400 WORDS)

The cost-effectiveness of treatment of supraventricular arrhythmias related to an accessory atrioventricular pathway: comparison of catheter ablation, surgical division and medical treatment

BACKGROUND

Treatment alternatives for patients with incapacitating supraventricular arrhythmias related to an accessory atrioventricular pathway include transcatheter radiofrequency (RF) ablation, surgical division and long-term antiarrhythmic therapy (medical).

AIM

The aim of this study was to compare in terms of cost and efficacy, transcatheter, surgical and medical treatment of patients with incapacitating supraventricular arrhythmias resulting from an accessory pathway.

METHODS

The study population consisted of 52 patients who underwent transcatheter RF ablation (20 consecutive patients), surgical treatment (20) and medical treatment (12). Two types of economic analysis were used. In all groups, a resource based costing method was used and in the medical and surgical treatment groups, a diagnostic related group (DRG) based costing method was used.

RESULTS

Eighteen out of 20 (90%) patients who underwent catheter ablation remained asymptomatic during 8.4 +/- 1.6 months of follow-up. All surgically treated patients remained asymptomatic during 54 +/- 15 months of follow-up. Only one of the 12 patients in the medical treatment group remained completely free of symptoms during the mean 58 +/- 23 month follow-up period. The mean cost (1992 Australian dollars) per patient, calculated on the basis of actual resources used (with a DRG based costing given in brackets), was $2746 +/- $800 for catheter ablation, $12141 +/- $4465 ($12880 +/- $3998) for surgical treatment and $1713 +/- $748 ($1967 +/- $33) for medical treatment. The total cost of management over 20 years is estimated to be: $2911 for catheter ablation, $17467 for surgery and $4959 for medical treatment.

CONCLUSIONS

In the long term transcatheter RF ablation is the most cost-effective treatment strategy for patients with incapacitating supraventricular arrhythmias related to an accessory pathway.

Mechanism of substance P-induced hyperpolarization of porcine coronary artery endothelial cells

Substance P (SP) is a potent endothelium-dependent vasodilator, and in porcine coronary arterioles the vasodilatory action of SP appears to be mediated entirely by nitric oxide. We tested the hypothesis that SP induces hyperpolarization in porcine coronary artery endothelial cells (PCAECs) by activating Ca(2+)-activated K+ (KCa) channels. With a bath Ca2+ concentration ([Ca2+]) of 1 mM, 10 nM SP elicited an increase in cytosolic [Ca2+] ([Ca2+]i) from a baseline of 25 +/- 4 nM to a peak of 808 +/- 120 nM, followed by a slowly declining plateau phase, which was absent in Ca(2+)-free bath and was abolished by addition of extracellular lanthanum or nickel. Whole cell current-clamp recordings revealed that the time course of SP-induced [Ca2+]i increases correlated closely with membrane hyperpolarization from an average resting potential of -42 +/- 2 to a peak of -79 +/- 2 mV. Under voltage clamp, SP stimulated whole cell currents with reversal potentials strongly dependent on extracellular K+ concentration. In 62% of patches tested, single-channel recordings revealed an intermediate-conductance K+ channel with activation highly correlated with the SP-induced [Ca2+]i increase. These results suggest that, in PCAECs, SP induces Ca2+ release from stores along with Ca2+ influx which activate a KCa channel leading to hyperpolarization. This may increase the driving force for Ca2+ entry and thus modulate endothelium-derived nitric oxide release.

Endothelial regulation of coronary microvascular tone under physiological and pathophysiological conditions

The endothelium has profound potential to modulate coronary arteriolar tone under a variety of physiological and pathophysiological situations. The endothelium in coronary microvessels is responsible for producing flow-dependent vasodilation, which is mediated by nitric oxide. The endothelium, however, does not mediate the myogenic response of coronary arterioles, but production of nitric oxide nevertheless modulates myogenic responses. The endothelium also has a role in coronary alpha-adrenergic vasoconstriction, because inhibition of nitric oxide synthesis augments coronary alpha 1 and alpha 2-adrenergic vasoconstriction. Other neurohumoral substances or autocoids also have their vasodilator actions mediated through the production of nitric oxide in coronary arterioles. Specifically, serotonin, adenosine diphosphate, and histamine all have their actions transduced through the production of nitric oxide. In the pathophysiological setting with impaired endothelial function, vasodilator responses to endothelium-dependent factors are significantly attenuated, and this can be reversed by administration of L-arginine. These impaired responses may contribute to the pathogenesis of ischaemic heart disease, especially that which occurs due to microvascular spasm.

A disease activity index: its use in clinical trials and disease assessment in patients with rheumatoid arthritis

Measuring disease activity is important in the assessment of patients with rheumatoid arthritis (RA). The value of composite indices in determining activity is discussed. A validated index, the Stoke index, has been used in clinical trials of combination therapy in patients with RA, both to evaluate efficacy and to stratify response to single-agent therapy before randomization to combination treatment. Disease activity determines the use of disease-modifying antirheumatic drugs. Should these drugs be used in mild RA when disease activity is low? Results of a study comparing hydroxychloroquine with placebo in this situation suggest that they should. Finally, the outcome of suppressing disease activity over a 5- to 10-year period is unknown. Measured either radiologically or functionally, preliminary data suggest that the lower the mean disease activity over time, the more favorable the outcome.

The relationship between serial measures of disease activity and outcome in rheumatoid arthritis

Disease activity was measured annually over a median period of 7 years (range 5-9) in a cohort of 127 patients with rheumatoid arthritis. The measurements were plotted, and the area under the resultant curve measured. The relationship of serial measures of disease activity (area under the curve) to outcome (measured radiologically, functionally and by global assessment) was investigated. A significant correlation was found between persistent disease activity and radiographic deterioration. Similar results were found for functional outcome, as measured by Steinbrocker grade, health assessment questionnaire score or global assessment (by analogue score). Single measures of disease activity did not predict outcome. Although imprecise, current methods of measuring disease activity in RA, if measured serially, are valuable in predicting outcome over a 5-10 year period.

Suspected cutaneous drug toxicity in rheumatoid arthritis--an evaluation

Cutaneous toxicity from drugs used to treat RA is a major perceived problem. Over a 2-yr period we have prospectively reviewed 114 patients with a suspected adverse cutaneous reaction to anti-rheumatic drugs. In 71 (62%), the rash was thought to be unrelated to drug therapy. This group included 10 in whom the rash had resolved before review (usually < 1 week), 38 with a rash related to their rheumatoid disease and 23 with eruptions unrelated to either drugs or arthritis. Forty-three (38%) patients had rashes thought to be related to their drug therapy. Gold therapy (both oral and intramuscular) was implicated most frequently (31 patients). However, the majority of these (23) had a pityriasiform/discoid eczematous eruption that responded to potent topical steroids occasionally with a reduction in gold dosage. In this sample it was possible to continue drug therapy in 82% of patients with what were initially thought to be cutaneous adverse drug reactions. Careful evaluation should allow a majority of patients to continue drug therapy from which they are often gaining benefit.

Transcatheter radiofrequency ablation. Early experience with supraventricular tachyarrhythmias related to accessory atrioventricular and dual atrioventricular nodal pathways

OBJECTIVE

To describe our initial experience with transcatheter radiofrequency ablation, a useful new treatment for supraventricular tachyarrhythmias related to the presence of an accessory atrioventricular (AV) pathway or dual atrioventricular nodal pathways.

PATIENTS AND METHODS

One hundred and ten patients, including 77 with accessory pathways, 32 with dual atrioventricular (AV) nodal pathways and one with both, underwent electrophysiological studies and were treated with transcatheter radiofrequency ablation in a large metropolitan teaching hospital.

RESULTS

Ninety-five patients (86%) were without evidence of accessory pathway conduction or inducible supraventricular tachycardia and were free of symptoms after a mean follow-up of 13 months (range, 3.0-51 months). Sixty-six of 79 accessory pathways (83.5%) were ablated including 42 of 46 left-sided (91%), 14 of 21 posteroseptal (66%), six of seven anteroseptal (86%), three of four right-sided and one of one midseptal pathways. Thirty-one patients with AV nodal reentry were successfully treated by ablation of either the slow (12 patients) or fast (19 patients) conducting AV nodal pathway. There was a progressive improvement in the success rate of the first procedure from 17% to 64% with the use of large-tip catheters and from 64% to 91% when a purpose-built radiofrequency generator was employed. Complications occurred in nine patients: cardiac tamponade (two patients); mild mitral regurgitation (four); subclavian vein thrombosis (one); transient cerebral ischaemic attack (one); and non-thrombocytic purpuric rash (one). These occurred predominantly during the early experience and were without long-term sequelae. Late in our experience, one patient developed complete atrioventricular block requiring permanent pacemaker implantation.

CONCLUSIONS

In this institution, radiofrequency catheter ablation has been a safe and effective treatment strategy for patients with life-threatening or highly symptomatic supraventricular arrhythmias.

An index of disease activity in rheumatoid arthritis

This paper describes the Stoke Index which has been designed to give a global measure of disease activity in rheumatoid arthritis. The index is based on two objective laboratory measurements, one subjective and two semi-objective clinical measurements, chosen from 13 measurements using clinical judgement. Variable selection routines in principal components analysis are used to demonstrate that the index measures clinically defined disease activity. Its sensitivity and reversibility are also considered. A comparison is carried out with another index (Mallya-Mace) and a modification is suggested.

Myogenic response gradient in an arteriolar network

Experiments were conducted to test the hypothesis that a longitudinal gradient in myogenic responsiveness exists within an arteriolar network. Single arterioles were dissected from the hamster cheek pouch, cannulated with micropipettes, and transferred to an inverted microscope for in vitro study. Pressure-diameter relationships of five branching orders of arterial vessels were measured in the presence of spontaneous vascular tone and after elimination of tone with a Ca(2+)-free solution containing nitroprusside. At luminal pressures matching those found in vivo, the diameters of the vessels with spontaneous tone were as follows: small arteries, 81 microns; first-order arterioles, 52 microns; second-order arterioles, 32 microns; third-order arterioles, 24 microns; and fourth-order arterioles, 11 microns. All branching orders of vessels exhibited true myogenic responses as indicated by negative slopes of their pressure-diameter relationships. Each vascular branching order exhibited its maximum myogenic responsiveness at a pressure near or just slightly higher than its normal pressure as measured in vivo. Relative myogenic responsiveness increased with decreasing vessel size down to the level of the second- and third-order arterioles, whereas fourth-order arterioles were substantially less responsive than third-order arterioles. A compilation of data from numerous in vivo and in vitro studies suggests that the same myogenic response pattern may be found in other vascular beds.

Undesirable mode switching with a dual chamber rate responsive pacemaker

The Telectronics 1250 Meta MV DDDR pacemaker is a new device featuring automatic mode switching from DDDR to VVIR pacing in the event of an atrial arrhythmia. Although mode switching is a valuable feature, sinus tachycardia can cause an undesirable mode switch to occur. Of 24 implants at this institution, 11 have been for an AV conduction disorder. Eight of these 11 patients were specifically evaluated for undesirable mode switching. During exercise testing and/or Holter monitoring, mode switching was repeatedly seen in seven of the eight at low levels of exercise. Factors precipitating mode switching were a low rate response factor, low upper rate setting, long base postventricular atrial refractory period (PVARP) and a long AV delay. During Holter monitoring, patients spent up to 50% of the time in VVIR pacing as opposed to DDDR pacing. It is concluded that patients with intact sinus node function are at risk of undesirable mode switching and should probably be programmed to the DDD mode unless there is a specific indication for DDDR pacing. If the DDDR mode is chosen, careful selection of the aforementioned pacing parameters is required.