Effects of atropine on diastolic time

The Electro-Mechanical window: a risk marker for Torsade de Pointes in a canine model of drug induced arrhythmias

BACKGROUND AND PURPOSE

In cardiovascular pharmacology, electrical and mechanical events can be distinguished, and the phrase 'electro-mechanical window' (EMw) describes the temporal difference between these events. We studied whether changes in EMw have potential predictive value for the occurrence of arrhythmias in fentanyl/etomidate-anaesthetized beagle (FEAB) dogs.

EXPERIMENTAL APPROACH

The EMw was calculated as differences between the QT interval and QLVP(end) in FEAB dogs during atrial pacing, treatment with isoprenaline or atropine, body temperature changes and induction of Torsade de Pointes (TdP) in an LQT1 model.

KEY RESULTS

The electrical systole (QT interval) was shorter than the duration of the mechanical event (QLVP(end) ), providing a positive EMw. Atrial pacing, atropine or body temperature changes had no major effects on EMw, despite large changes in QT duration. However, β-adrenoceptor stimulation (with isoprenaline) decreased the EMw (from 90 to 5 ms) and in combination with HMR1556, a blocker of the slowly activating potassium current (I(Ks) ), induced a large negative EMw (-109ms) and TdP. Prevention of TdP by atenolol or verapamil was associated with a less negative EMw (-23 to -16ms). Mexiletine, a poorly effective long QT treatment, did not affect the EMw or prevent TdP induction.

CONCLUSIONS AND IMPLICATIONS

The EMw is a marker, other than QT prolongation, of TdP risk in the FEAB model. Therefore, we suggest examining the EMw as a risk marker in cardiovascular safety studies and as a potential biomarker to improve clinical management of long QT syndrome patients, especially in patients with borderline QT prolongation.

The Systolic to Diastolic Duration Ratio in Children with Hypoplastic Left Heart Syndrome: A Novel Doppler Index of Right Ventricular Function

BACKGROUND

Right ventricular (RV) function is an important determinant of clinical status in children with hypoplastic left heart syndrome (HLHS). However, assessment of RV function remains challenging because of its complex morphology. We investigated the S/D duration ratio in children with HLHS as a novel index of global RV function.

METHODS

We measured systolic (S) and diastolic (D) duration using tricuspid regurgitation duration from Doppler flow, to calculate the S/D ratio in 33 children with HLHS and 33 control subjects matched for age and sex. We compared the S/D ratio between patients with HLHS and control subjects, between patients with HLHS and normal and abnormal RV function, and between patients with HLHS at different stages of palliation. We further correlated the S/D ratio with catheterization data.

RESULTS

Patients and control subjects were well matched for age (3.12 +/- 4.5 vs 3 +/- 4.5 years, not significant) sex, and heart rate (cycle length 524 +/- 179 vs 575 +/- 162 milliseconds, not significant). Patients with HLHS had a significantly higher S/D ratio than control subjects (1.65 +/- 0.85 vs 0.85 +/- 0.2, P < .0001). The S/D ratio became increasingly elevated in HLHS at higher heart rates, but not in control subjects. The S/D ratio was significantly higher in patients with HLHS and decreased RV function as compared with patients with HLHS and normal RV function (2.2 +/- 0.7 vs 1.5 +/- 0.47, P = .006), and significantly increased in patients with Norwood stage 1 versus patients with Norwood stages 2 and 3 HLHS (2.16 vs 1.4 and 1.32, respectively, P < .01 and P < .001, respectively). The S/D ratio did not correlate with catheterization-derived RV end-D pressure or cardiac index.

CONCLUSIONS

Patients with HLHS have an increased S/D ratio as a result of a shortened D and prolonged S. Measurement of the S/D duration ratio using Doppler flow is a novel method to augment assessment of global RV function in HLHS.

The systolic to diastolic duration ratio in children with heart failure secondary to restrictive cardiomyopathy

Systole (S) and diastole (D) are fundamental to cardiac function, yet their durations are not routinely evaluated. We defined the S/D duration ratio in 11 children with restrictive cardiomyopathy (CM) and 31 control subjects, using tricuspid regurgitant flow duration. We correlated S/D ratio, S duration, and D duration with heart rate and compared groups. Heart rates of control subjects and patients with restrictive CM were similar (P = .995). The S/D ratio was higher in patients with restrictive CM than in control subjects (1.6 +/- 0.81 vs 0.8 +/- 0.19, P < .001) as a result of shortened D (0.43 +/- 0.13 vs 0.56 +/- 0.06, P < .01) and prolonged S (0.58 +/- 0.12 vs 0.44 +/- 0.06, P < .01). The S/D ratio was highly correlated to heart rate in restrictive CM (r = 0.95, P < .0001). The high S/D ratio found in restrictive CM, found also in dilated CM, suggests that this index is generic to heart failure rather than to a specific disease. The S/D ratio is easily measured using Doppler flow, enhancing echocardiographic assessment of D function in children.

Cardiac ventricular diastolic and systolic duration in children with heart failure secondary to idiopathic dilated cardiomyopathy

Systole and diastole are the fundamental periods of the cardiac cycle, yet little emphasis has been placed on their relative duration when evaluating heart failure. Cardiac intervals are used to assess ventricular function, but the relative duration of systole and diastole for defining function have not been evaluated. We hypothesized that in heart failure, systole is prolonged and diastole shortened. We defined systole and diastole in 16 children with idiopathic dilated cardiomyopathy and in 16 normal controls, matched for age and gender, using the mitral regurgitant (MR) and tricuspid regurgitant (TR) flow duration. The systole and diastole durations (expressed as a fraction of the cardiac cycle) were correlated with heart rate and age and compared between groups. The subjects were compared with gender- and age-matched controls (9.98 +/- 6.1 vs 9.88 +/- 6.08 years, p = NS). The 2 groups had similar heart rates (104 +/- 31 vs 92 +/- 34 beats/min, p = NS). The systole duration was not significantly different when measured by MR versus TR duration (0.60 +/- 0.10 vs 0.57 +/- 0.11 of the cardiac cycle, respectively, p = NS). Systole was prolonged in subjects compared with controls (0.60 +/- 0.1 vs 0.42 +/- 0.08, respectively, using MR duration, p < 0.0001 and 0.57 +/- 0.11 vs 0.41 +/- 0.07, respectively, using TR duration, p = 0.0008). The systolic/diastolic ratio was 0.77 +/- 0.24 in the controls versus 1.57 +/- 0.98 in the patients with idiopathic dilated cardiomyopathy using the TR duration (p < 0.005) and 1.67 +/- 0.68 using the MR duration (p < 0.0001). The systole duration correlated with heart rate in subjects (r = 0.79, p = 0.0003) and controls (r = 0.69, p = 0.003). In conclusion, systole is significantly prolonged and diastole correspondingly shortened in heart failure. Reversal of the normal systolic/diastolic ratio may compromise cardiac filling and function. The systole and diastole duration are easily measured using routine Doppler flow, enhancing assessment of cardiac function in children.

Diastolic heart function--pathophysiology, characterization, and therapeutic approaches

In recent years diastolic cardiac function has attracted increasing attention since parameters of diastolic function were found to be altered earlier or more specifically than parameters of systolic function. Diastolic cardiac function is determined by both active (muscular relaxation, redistribution of calcium, synchronization, etc.) and passive (myocardial structure, fibrosis, etc.) factors. As a consequence, a comprehensive assessment of diastolic cardiac function cannot be based on one single parameter. For a complete analysis of diastolic function it is necessary to perform invasive diagnostic procedures involving the measurement of atrial and ventricular pressures, as well as the registration of volume changes with a high time resolution. In addition, it is necessary to measure wall thickness and ventricular configuration, so that apart from filling parameters the stress-strain relationship can be obtained. Noninvasive techniques (Doppler echocardiography, radionuclear ventriculography, apexcardiography) may suggest alterations in diastolic function as well. They ought to be complemented by additional diagnostic procedures (pulmonary pressure, stress testing, etc.). Therapy must consider potentially harmful effects on diastolic function parameters, particularly if changes in myocardial oxygen consumption may result (heart rate, parietal wall stress). Calcium antagonists (verapamil, diltiazem, nifedipine), phosphodiesterase inhibitors (milrinone), beta-adrenergic agonists and antagonists with vasodilating effects (e.g., celiprolol) all have beneficial effects on diastolic myocardial function. A range of diastolic function parameters is being reviewed in the following paper. Their role in the estimation of cardiac function and their responsiveness to therapy in hypertrophy, cardiomyopathy, and coronary heart disease is being discussed.

Reduction of ventricular arrhythmias by atropine during coronary arteriography

Sustained ventricular arrhythmia is a well-recognized complication of cardiac catheterization, often occurring after selective coronary artery injection of contrast medium. The role of autonomic reflexes in the pathogenesis of this phenomenon is unclear. Although the muscarinic antagonist atropine is often administered prophylactically before coronary angiography to reduce the likelihood of sinus bradycardia and vasovagal reactions, its influence on ventricular arrhythmias in this setting has not been established. This case-control trial studied 648 patients undergoing coronary arteriography to investigate this issue. Eleven case subjects (those with ventricular tachyarrhythmia) were identified. Control subjects (those without ventricular tachyarrhythmia) were matched for baseline heart rate (+/- 6 beats/min), age (+/- 10 years), sex and calendar year of procedure using a 1:3 sampling ratio. All 26 potential clinical, anatomic and hemodynamic covariates were statistically similar between groups. Ventricular tachyarrhythmias were more likely to occur after selective right coronary injection (odds ratio 15.1, p = 0.0008) but not after multiple contrast injections (odds ratio 0.918, difference not significant). Most importantly, atropine sulfate was administered prophylactically to 18 of 33 control subjects (55 +/- 9%) but only 1 of 11 cases (9 +/- 9%), generating a significant odds ratio of 12.0 (p = 0.02). Thus, the odds of experiencing sustained ventricular tachyarrhythmias during coronary arteriography may potentially be reduced 12-fold by prior administration of atropine, even in patients with normal baseline heart rates.

Cardiovascular and hypokalaemic effects of inhaled salbutamol, fenoterol, and isoprenaline

The cardiovascular and hypokalaemic effects of equal doses of inhaled fenoterol, isoprenaline and salbutamol were compared in eight healthy male volunteers, in a double blind, placebo controlled study. Increasing doses of 400, 600, and 800 micrograms were given from a metered dose inhaler at 15 minute intervals, followed by measurements of heart rate, blood pressure, total electromechanical systole (as a measure of inotropic response), QTc interval, and plasma potassium concentration. After repeated inhalation, fenoterol resulted in significantly greater chronotropic, electrocardiographic, and hypokalaemic effects than either isoprenaline or salbutamol. The maximum inotropic effect of fenoterol was similar to that of isoprenaline.

The effect of ionizing radiation on advanced life support medications

Advanced life support medications stored in emergency department stretcher areas, diagnostic radiology rooms, and radiotherapy suites are exposed to ionizing radiation. We hypothesized that radiation may decrease the potency and thus the shelf life of medications stored in these areas. Atropine, dopamine, epinephrine, and isoproterenol were exposed to a wide range of ionizing radiation. The potency of the four drugs was unaffected by levels of radiation found in ED stretcher areas and high-volume diagnostic radiograph rooms (eg, chest radiograph, computed tomography, fluoroscopy). The potency of atropine may be reduced by gamma radiation in high-use radiotherapy suites. However, dopamine, epinephrine, and isoproterenol were unaffected by high doses of gamma radiation. Atropine, dopamine, epinephrine, and isoproterenol may be safely kept in ED stretcher areas and diagnostic radiology rooms without loss of potency over the shelf life of the drugs.

Cardiovascular effects of caffeine in elderly men

Ten healthy elderly male volunteers were given 4 mg/kg of caffeine by intravenous infusion on three separate occasions. This resulted in mean peak plasma concentrations of caffeine of 7.4 +/- 0.7 micrograms/ml. Immediately after each of the three caffeine infusions, the mean systolic blood pressures increased 14, 7, and 16 mm Hg, and the mean diastolic blood pressures increased 7, 4, and 7 mm Hg, respectively. Both the systolic and the diastolic blood pressures returned to preinfusion values within 4 hours. The QS2 index and the left ventricular ejection time (LVET) index increased after caffeine, probably as a result of the caffeine-induced increase in arterial blood pressure. The pre-ejection period (PEP), the PEP/LVET ratio, and the diastolic time remained unchanged. Caffeine, in doses equal to those contained in 2 to 3 cups of coffee, produces an increase in blood pressure but has no demonstrable positive inotropic effect in healthy elderly men.

Comparison of the inotropic and chronotropic effects of metoprolol and propranolol

The cardiovascular responses to intravenous doses of isoproterenol were measured in eight male volunteers before and during administration of 50 mg metoprolol, orally every 6 hours and 40 mg propranolol, orally every 6 hours for a total of five doses. The dose of isoproterenol required to produce an increase in heart rate of 25 beats/min (the ID25) was 2.0 +/- 1.4 microgram before beta blockade, 6.2 +/- 4.4 microgram during metoprolol, and 44.4 +/- 12.0 microgram during propranolol administration. Similar changes in diastolic blood pressure, QS2I, preejection period, and preejection period/left ventricular ejection time ratio occurred at the ID25 during treatment with both metoprolol and propranolol. In volunteers, propranolol produces a much more intense blockade of the inotropic and chronotropic effects of isoproterenol than does metoprolol.

Cardiovascular effects of theophylline. Partial attenuation by beta-blockade

The effects of theophylline upon cardiovascular function were studied in 8 male subjects, aged 22-33 years, before and during concomitant administration of metoprolol (50 mg every 6 h) and propranolol (40 mg every 6 h). Theophylline, as aminophylline (6.7-7.3 mg/kg) was given over 30 min. The theophylline level five minutes after completion of the aminophylline infusion was 15.9 +/- 1.8 micrograms/ml in the absence of beta blockade, 16.1 +/- 1.7 micrograms/ml during metoprolol, and 15.1 +/- 1.6 micrograms/ml during propranolol. Theophylline produced a 7% increase in mean arterial pressure which was not attenuated by either metoprolol or propranolol. Heart rate was not changed by theophylline. The QS2 Index (QS2I), a sensitive indicator of inotropism, was shortened from 488 +/- 16 to 476 +/- 16 msec (p less than 0.01) by theophylline alone. After administration of metoprolol or propranolol, theophylline produced no shortening of the QS2I. Theophylline has a mild inotropic effect in healthy subjects. This effect is prevented by pretreatment with beta-adrenergic antagonists.