Effect of exercise-induced ischemia on QT interval dispersion

An increased spatial dispersion of ventricular repolarization duration (QT dispersion) is associated with an increased vulnerability to arrhythmias. This study was designed to examine the effect of exercise on QT dispersion in ischemic heart disease (IHD). QT dispersion, corrected QT dispersion, and percentage change in uncorrected and corrected QT dispersion between rest and peak exercise were examined in 14 members of a control group, 17 patients with IHD, and 14 patients with IHD who were receiving beta-blockers (IHD-B). All subjects had undergone a standard Bruce protocol exercise test, and QT intervals were measured at rest and peak exercise with a digitizing tablet interfaced to a personal computer. QT dispersion at rest was markedly increased in the IHD group compared with that in the control and IHD-B groups, respectively (corrected QT dispersion in milliseconds), 74 +/- 7, 40 +/- 4, 49 +/- 5, p < 0.03). The corrected QT dispersion at peak exercise was greater in the IHD group compared with that in the control group (57 +/- 5 vs 26 +/- 3 msec, p < 0.03). The percentage change in QT dispersion with exercise was significantly higher in the IHD group (52% +/- 5%) compared with that in both the control group (28% +/- 4%, p < 0.002) and the IHD-B group (30% +/- 3%, p < 0.01). A larger mean QT dispersion at peak exercise and an increased percentage change in QT dispersion with exercise may help explain the increased susceptibility of the IHD group for arrhythmias. The cardioprotective action of beta-blockers may be explained by their blunting effect on exercise-related changes in QT dispersion.

Large airway obstruction by a chronic dissecting aortic aneurysm in the Marfan syndrome

We describe a patient with the Marfan syndrome who presented with an acute aortic dissection. She underwent composite graft replacement of the aortic root. She returned two years later with dyspnoea and stridor due to tracheal compression by a large chronic dissection of the thoracic aorta. Marfan patients are at risk of chronic dissection involving the remaining distal aorta and require regular noninvasive assessment following surgery.

Effects of hypertrophy on regional action potential characteristics in the rat left ventricle: a cellular basis for T-wave inversion?

BACKGROUND

In cardiac hypertrophy, ECG T-wave changes imply an abnormal sequence of ventricular repolarization. We investigated the hypothesis that this is due to changes in the normal regional differences in action potential duration. We assessed the contribution of potassium- and calcium-dependent currents to these differences. Both the altered sequence of ventricular repolarization and the underlying cellular mechanisms may contribute to the increased incidence of ventricular arrhythmias in hypertrophy.

METHODS AND RESULTS

Rats received daily isoproterenol injections for 7 days. Myocytes were isolated from basal subendocardial (endo), basal midmyocardial (mid), and apical subepicardial (epi) regions of the left ventricular free wall. Action potentials were stimulated with patch pipettes at 37 degrees C. The ratio of heart weight to body weight and mean cell capacitance are increased by 22% and 18%, respectively, in hypertrophy compared with controls (P<.001). Normal regional differences in action potential duration at 25% repolarization (APD25) are reduced in hypertrophy (control: endo, 11.4+/-0.9 ms; mid, 8.2+/-0.9 ms; epi, 5.1+/-0.4 ms; hypertrophy: endo, 11.6+/-0.9 ms; mid, 10.4+/-0.8 ms; epi, 7.8+/-0.6 ms). The regional differences in APD25 are still present in 3 mmol/L 4-aminopyridine. Hypertrophy affects APD75 differently, depending on the region of origin of myocytes (ANOVA P<.05). APD75 is shortened in subendocardial myocytes but is prolonged in subepicardial myocytes (control: endo, 126+/-7 ms; epi, 96+/-10 ms; hypertrophy: endo, 91+/-6 ms; epi, 108+/-7 ms). These changes in APD75 are altered by intracellular calcium buffering.

CONCLUSIONS

Normal regional differences in APD and the changes observed in hypertrophy are only partially explained by differences in I(tol). In hypertrophy, the normal endocardial/epicardial gradient in APD75 appears to be reversed. This may explain the T-wave inversion observed and will have implications for arrhythmogenesis.

Evaluation of group processes in the professional development of mental health nurses

The purpose of this paper is to report on group process data for 41 registered nurses endorsed as psychiatric nurses. Profile analysis was used to evaluate the flatness of ratings of group interaction by two groups of participants. Accelerated professional development participants had non-flat rating profiles for their ratings of how far group sessions helped them to clarify or validate issues, focused on the 'reasons for' and consequences of session content, achieved resolution of different points of view, or promoted consensus and group cohesiveness. The peer consultation participants had a non-flat rating profile for overall group supportiveness, demonstrating that the participants felt less supported over time.

Regional differences in electrical and mechanical properties of myocytes from guinea-pig hearts with mild left ventricular hypertrophy

OBJECTIVE

To investigate electrical and mechanical properties of single myocytes isolated from different regions of the left ventricle in control and hypertrophied hearts.

METHODS

Mild cardiac hypertrophy was induced in guinea-pigs by aortic constriction. Myocytes were isolated from basal sub-endocardial, basal mid-myocardial and apical sub-epicardial layers of the left ventricle. Action potentials were stimulated at 1 Hz. Membrane currents were measured using the switch-clamp technique. Cell shortening was measured using a photodiode array.

RESULTS

In control hearts mean action potential duration (APD) was longer in sub-endocardial myocytes than in sub-epicardial myocytes. In hypertrophy APD was prolonged in sub-epicardial and mid-myocardial myocytes and unchanged in sub-endocardial myocytes (APD90 ms, control: sub-endocardial 273 +/- 12, mid-myocardial 254 +/- 14, sub-epicardial 229 +/- 9; hypertrophy: sub-endocardial 259 +/- 13, mid-myocardial 291 +/- 9, sub-epicardial 268 +/- 11, P < 0.005, ANOVA). There was no significant regional difference in APD in hypertrophied hearts. In control hearts L-type calcium current (ICa) was similar in all regions. In hypertrophy ICa was increased in sub-epicardial and mid-myocardial myocytes and reduced in sub-endocardial myocytes. Calcium-activated tail currents were not regionally different in control or hypertrophied hearts, but were increased in hypertrophy.

CONCLUSIONS

Changes in electrical and mechanical properties associated with hypertrophy are not homogeneous throughout the left ventricle. The difference in APD between sub-endocardial and sub-epicardial myocytes seen in control hearts is lost in hypertrophy. These results may favour the propagation of re-entry arrhythmias in hypertrophied hearts.

A UK survey of nuclear medicine imaging performance using the TransBone anthropomorphic phantom

In March 1993, the British Nuclear Medicine Society was approached and agreed to take part in an international nuclear medicine quality survey organized jointly by the World Health Organization and the International Atomic Energy Agency. The study involved the use of a novel anthropomorphic transmission phantom, which contained a number of abnormalities of varying contrast. The UK part of the survey was undertaken during April and May 1994. A total of 14 departments took part in the study, using a total of 25 gamma cameras. For each gamma camera tested, imaging was performed using the same camera set-up, imaging and hard copy parameters normally used for recording bone images. The test image was then reported by the usual clinical image reporter according to a fixed protocol and a 4-point scoring system. The results varied widely, with 62% of all reportable locations using all four possible scores between the centres being tested. The sensitivity and specificity ranged from 40 to 80% and 59 to 100% respectively. Calculated ROC areas ranged from 65 to 94% with a mean of 80%. The survey methodology means that a relatively large number of factors affect the overall results, of which the main factor appears to be reporting accuracy.

The sexual behaviour of international travellers at two Glasgow GUM clinics. Glasgow genitourinary medicine

A survey of patients attending 2 Glasgow genitourinary medicine (GUM) clinics was conducted in 2 3-month periods in 1993 and 1994. Three hundred and twenty-five attendees who had travelled abroad in the preceding 3 months completed anonymous self-administered questionnaires about their sexual behaviour during these recent journeys abroad. There were 112 women and 213 men (185 heterosexuals and 28 homosexuals). Twenty-two (19.6%) women, 56 (31%) heterosexual men and 13 (42%) homosexual men had a sexual contact with a new partner while abroad. Of those who had had a new sexual contact abroad, 11 women (50% of those who had sex with a new partner) and 33 heterosexual men (59% of those who had sex with a new partner) were inconsistent users of condoms. Analysis of data found that homosexual and heterosexual men, and business travellers, are at increased risk of exposure to sexually transmitted diseases, including HIV infection, and should be targeted with safer sex health promotion prior to travel.

QT interval dynamics and heart rate variability preceding a case of cardiac arrest

A 71 year old man with hypertensive heart disease and chronic renal failure was wearing a Holter monitor when he had a cardiac arrest. He had ventricular fibrillation (VF) and died despite prompt resuscitation. In the 15 minutes preceding the VF there was a sudden increase in heart rate, followed by a brief period of atrial fibrillation leading to ventricular tachycardia, which in turn rapidly degenerated into VF. The QT interval and heart rate variability were studied half hourly over the seven hours preceding the cardiac arrest, using a computerised Holter system. A further detailed analysis was performed over the final hour before the cardiac arrest. An abrupt increase in the steepness of the QT/RR slope, a prolonged QTc, and a reduction in the heart rate variability were observed in the interval that immediately preceded the onset of the terminal rhythm disturbance.

Left ventricular hypertrophy in hypertensive patients is associated with abnormal rate adaptation of QT interval

OBJECTIVES

This study sought to examine whether the responses of the QT interval to changes in the heart rate were altered in left ventricular hypertrophy (LVH).

BACKGROUND

The QT interval has been shown to have a delayed adaptation to sudden changes in heart rate in normal subjects. Abnormalities in the adaptation of the QT interval to changes in the RR interval may facilitate the development of ventricular arrhythmias.

METHODS

Consecutive newly diagnosed hypertensive subjects, not taking any medications, were age and gender matched for LVH (n = 21) versus on LVH (n = 16). QT interval dynamics were analyzed under visual control using a validated algorithm with automatic QT measurements at the end of the T wave. A computerized Holter system was developed to study the QT interval response to changes in the RR interval. The adaptive response of the QT interval was measured as the ratio of the slope from 10% to 90% of the QT change relative to the RR interval change (dQT/dRR10-90). Steady state adaptation was also studied as the percent shortening and lengthening of the QT interval during acceleration and deceleration of heart rate.

RESULTS

The adaptive response of the QT interval measured as dQT/dRR10-90 was increased in the LVH group compared with that in the control subjects during both acceleration (0.33 +/- 0.06 vs. 0.18 +/- 0.02, p = 0.02) and deceleration phases (0.23 +/- 0.04 vs. 0.16 +/- 0.02, p = 0.03). In the LVH group, the percent lengthening of the QT interval was greater (7.6 +/- 0.7 vs. 5.1 +/- 0.2, p = 0.03), whereas the percent shortening was not significantly different (5.71 +/- 0.5 vs. 4.6 +/- 0.3, p = 0.43), than that in control subjects.

CONCLUSIONS

The QT interval response to changes in the RR interval is rapid and exaggerated in LVH. These abnormalities of the QT interval response demonstrate that there are altered repolarization dynamics in patients with LVH that may make them vulnerable to serious ventricular arrhythmias.

L-type calcium current in catecholamine-induced cardiac hypertrophy in the rat

This study investigates whether an increase in L-type calcium current (ICa) could explain the prolongation of the action potential associated with the cardiac hypertrophy produced by repeated administration of isoprenaline. Hypertrophy was induced by daily injection of isoprenaline (5 mg/kg i.p.) for 7 days in male Wistar rats. Under whole-cell voltage-clamp conditions, ICa was evoked in Na(+)- and K(+)-free solution, by step depolarizations from a holding potential of -45 mV in single left ventricular myocytes isolated from control and hypertrophied rat hearts. In the test group, heart weight to body weight ratio and cell membrane capacitance were increased by 30 and 34%, respectively. Peak ICa was increased by 26% (control, -1.46 +/- 0.06 nA, n = 17; hypertrophy, -1.85 +/- 0.13 nA, n = 19; P < 0.02). However, when normalized for cell capacitance, there was no significant difference in peak current density (control, -12.1 +/- 0.5 pA/pF; hypertrophy, -11.5 +/- 0.6 pA/pF). The voltage dependence of ICa was similar in both cell types. No change was observed either in the steady-state activation or inactivation kinetics, or in the time course of inactivation. The recovery from inactivation of ICa, when fitted with monoexponential function with time constant tau rec, was not changed significantly by hypertrophy (control, tau rec = 115 +/- 23 ms, n = 9; hypertrophy, tau rec = 120 +/- 12 ms, n = 15). The increased calcium current occurs in parallel with the increase in cell size. The prolonged action potential duration seen in this model must be explained by changes in currents other than L-type calcium current.

Transient outward current in catecholamine-induced cardiac hypertrophy in the rat

We have demonstrated that a daily injection of isoproterenol (5 mg/kg ip) for 7 days induces a 30% increment in heart weight-to-body weight ratio and prolongs the action potential duration (APD) in male Wistar rats. The underlying mechanism of the prolonged APD was investigated in this model of hypertrophy by measuring the transient outward potassium current (Ito) in left ventricular myocytes of the rat with whole cell voltage-clamp techniques. Cell membrane capacitance was increased by 39%: 122 +/- 3 (n = 23) and 171 +/- 5 (SE) pF (n = 20) in control and hypertrophy, respectively (P < 0.001). Ito was evoked in sodium-free solutions containing 0.5 mM Ca2+ and 2 mM Co2+ by step depolarizations from a holding potential of -80 mV. The amplitude of the 4-aminopyridine-sensitive Ito (at 70 mV) was reduced by 28% in hypertrophy: 3.2 +/- 0.3 (n = 23) and 2.3 +/- 0.4 (SE) nA (n = 20) in control and hypertrophy, respectively (P < 0.05). When normalized for cell capacitance, the reduction was much larger: 26.4 +/- 2.5 and 13.1 +/- 1.8 pA/pF in control and hypertrophy, respectively (P < 0.001). The voltage dependence of Ito was similar in both cell types. No change was observed in the steady-state activation and inactivation kinetics in the two groups, nor was there a change in the time dependence of inactivation. The recovery from inactivation of Ito when fitted with a monoexponential function was not changed significantly in hypertrophy: time constants = 8.2 +/- 0.4 (n = 13) and 8.3 +/- 0.3 ms (n = 12) in control and hypertrophy, respectively. These results show that Ito density is decreased in catecholamine-induced cardiac hypertrophy, but current kinetics are not affected. The reduced Ito density may underlie the prolongation of APD in this model of hypertrophy.

Improvements in long term phototherapy for patients with Crigler-Najjar syndrome type I

Patients with Crigler-Najjar syndrome Type I are being treated with long-term blue-light phototherapy into childhood, adolescence and beyond. Phototherapy systems adapted from sunbed-type bases fitted with blue-emitting fluorescent tubes have been described. These systems provided higher irradiances and improved patient compliance compared with overhead therapy systems used in neonatal phototherapy. The acrylic bases of such units are, however, not designed to provide adequate levels of comfort for prolonged treatment in the long term. Previous work has shown that layer(s) of transparent 'bubble-wrap' can be used to address this problem, although the material absorbs light and provides lower levels of comfort for older or larger patients. We have used designs of transparent plastic lilos that provide better cushioning, although tend to puncture, and share with bubble-wrap a low porosity leading to patient discomfort. We have investigated the use of standard mesh and high-transmission fabrics stretched over an adjustable-tension frame. This method in particular combines a high degree of comfort with a clinically effective blue-light irradiance level, and hence appears to provide a satisfactory method of phototherapy delivery. The development of higher transmission materials offers further potential for improvement.

Suppression of oxidant production by diltiazem, nifedipine and verapamil in human neutrophils

1. Polymorphonuclear leucocytes are a major source of toxic oxidants in vivo, causing tissue injury in certain circumstances such as ischaemia and reperfusion. Calcium ions are a key mediator in the production of oxidants by these cells. The aim of this study was to examine the effects of the widely used calcium antagonists diltiazem, nifedipine and verapamil on the production of oxidants in neutrophils. 2. Human neutrophils were freshly prepared, suspended in different luminol media and mixed with varying amounts of each calcium antagonist. They were then stimulated with either serum-opsonized zymosan or phorbol 12-myristate 13-acetate. Oxidant production was determined by three methods, namely luminol-enhanced chemiluminescence, oxygen consumption and cytochemical staining. 3. Calcium antagonists inhibited oxidant production by neutrophils. IC50 values for diltiazem, nifedipine and verapamil in calcium-free medium were 0.32 mmol/l (SEM 0.02), 0.27 mmol/l (SEM 0.02) and 0.24 mmol/l (SEM 0.02) respectively under zymosan stimulation, and 0.33 mmol/l (SEM 0.02), 0.26 mmol/l (SEM 0.02) and 0.13 mmol/l (SEM 0.07) respectively under phorbol 12-myristate 13-acetate stimulation. These effects were independent of the presence of Ca2+ in the extracellular solution. Some inhibition was also observed when the calcium antagonists were added during the course of a respiratory burst. Oxygen uptake by the cells was reduced in the presence of each calcium antagonist. Phagocytosis by the stimulated neutrophils was not affected despite inhibition of oxidant production. 4. We conclude that calcium antagonists can suppress the capacity of neutrophils to produce oxidants. This result may provide a novel explanation for the observation that delayed treatment with calcium antagonists may attenuate post-ischaemic myocardial dysfunction.

Effects of neuropeptide Y on L-type calcium current in guinea-pig ventricular myocytes

1. Neuropeptide Y (NPY) reduces cell shortening at high concentrations in guinea-pig ventricular myocytes. We have studied the effects of the peptide on calcium current in cardiac myocytes. 2. We have recorded L-type calcium current in guinea-pig ventricular myocytes under conditions in which the effects of other overlapping currents have been minimised by using Na(+)-free, K(+)-free external solution and patch-clamp electrodes containing Cs+. 3. Peak inward calcium current is reduced by NPY at concentrations in excess of 1 nM, and maximal inhibition (31%) was found at and above concentrations of 100 nM. The IC50 value for NPY inhibition of peak calcium current was 1.72 nM. 4. NPY had no effect on the voltage-dependence of calcium current amplitude, on the time course of current inactivation, or on the voltage-dependence of the steady-state gating variables. 5. NPY did not reduce the calcium current in the presence of 8-Br-cyclic AMP, and it was also without effect when GTP-gamma-S or GDP-beta-S were included in the patch pipette. 6. We conclude that in guinea-pig ventricular myocytes NPY acts at low concentration to reduce L-type calcium current, via a G-protein-mediated pathway and reduction in intracellular cyclic AMP.

Client follow-up at the Adelaide sexually transmitted disease clinic

This study investigated the extent to which doctor-client communication is associated with follow-up rates at Clinic 275, an Adelaide sexually transmitted diseases (STD) clinic. At Clinic 275, clients are routinely screened for the major STDs at their first visit. They are then asked to return in one week's time for their results and further treatment if necessary. Over a four-week period in April-May 1994, the clinical consultations between doctors and 100 clients attending for their first visit in an episode of care were observed and recorded. Data from the observation schedules were matched with data collected from interviews, either when clients returned for their follow-up visit (n = 78) or from a telephone interview when they failed to return (n = 20). In addition, 18 clients who failed to return for follow-up (but were not part of the original observation sample) were interviewed. Sociodemographic factors did not affect follow-up rates. Of those who did not return for follow-up, social and environmental reasons were cited by about two-thirds. Reasons given by the remaining clients indicate that failure to return for follow-up was related to discrepancies in doctor-client communication in that they were confused about the need to return to obtain test results. In addition, approximately half could not name the infections for which they had been tested. Changes in clinic practice may prove a more useful method of increasing follow-up rates than seeking to identify the characteristics of noncompliant individuals.