Idiopathic ventricular fibrillation - Long term prognosis in relation to clinical findings and ECG patterns in a Swedish cohort.

BACKGROUND: Idiopathic ventricular fibrillation (IVF) is a rare cause of sudden cardiac arrest which may pose therapeutic and prognostic challenges. To date, the only effective treatment for survivors of cardiac arrest is the insertion of an implantable cardioverter-defibrillator (ICD). We sought to review the long-term outcome of a Swedish cohort with IVF. METHODS AND RESULTS: Fifty patients with IVF diagnosis between 1988 and 2016 (mean age at index 34.3, 56% male), were followed for a median 13.8 years in this retrospective multicenter observational study. No cardiac mortality was reported. 32% (n = 16) of patients had recurrence of ventricular fibrillation or sustained ventricular tachycardia, requiring ICD therapy, at a median time of 1.9 years (range 0.1-20.3) from the index event. Annual incidence rate of ventricular tachyarrhythmia was 3.1%. Abnormal ECG at baseline did not predict appropriate ICD therapy (p = 0.56). During the follow-up period, 14% (n = 7) patients received a cardiac diagnosis. Follow-up genetic testing was low (26%), however did confirm pathogenic mutations in three cases. CONCLUSION: Idiopathic VF is a rare diagnosis with a relatively good prognosis provided ICD therapy is initiated. Routine clinical follow-up is recommended due to potential late emerging cardiac pathology. ECG changes are common, but have no prognostic value in determining the risk of ventricular arrhythmias recurrence. Screening for genetic diseases has previously been low, and this calls for improvement, especially since cheaper and more comprehensive genetic panels are now readily available.

Defibrillation before EMS arrival in western Sweden.

BACKGROUND: Bystanders play a vital role in public access defibrillation (PAD) in out-of-hospital cardiac arrest (OHCA). Dual dispatch of first responders (FR) alongside emergency medical services (EMS) can reduce time to first defibrillation. The aim of this study was to describe the use of automated external defibrillators (AEDs) in OHCAs before EMS arrival. METHODS: All OHCA cases with a shockable rhythm in which an AED was used prior to the arrival of EMS between 2008 and 2015 in western Sweden were eligible for inclusion. Data from the Swedish Register for Cardiopulmonary Resuscitation (SRCR) were used for analysis, on-site bystander and FR defibrillation were compared with EMS defibrillation in the final analysis. RESULTS: Of the reported 6675 cases, 24% suffered ventricular fibrillation (VF), 162 patients (15%) of all VF cases were defibrillated before EMS arrival, 46% with a public AED on site. The proportion of cases defibrillated before EMS arrival increased from 5% in 2008 to 20% in 2015 (p<0.001). During this period, 30-day survival increased in patients with VF from 22% to 28% (p=0.04) and was highest when an AED was used on site (68%), with a median delay of 6.5min from collapse to defibrillation. Adjusted odds ratio for on-site defibrillation versus dispatched defibrillation for 30-day survival was 2.45 (95% CI: 1.02-5.95). CONCLUSIONS: The use of AEDs before the arrival of EMS increased over time. This was associated with an increased 30-day survival among patients with VF. Thirty-day survival was highest when an AED was used on site before EMS arrival.

Prevalence of diastolic dysfunction in patients with ankylosing spondylitis: a cross-sectional study.

OBJECTIVES: To determine the prevalence of diastolic dysfunction (DD) in patients with ankylosing spondylitis (AS) by following recommended criteria from the American Society of Echocardiography (ASE) and using single variables reflecting DD. METHOD: A total of 187 patients with AS (105 men; mean age 51 ± 13 years; mean duration of disease 15 ± 11 years) fulfilled the inclusion criteria and underwent pulsed-wave and tissue Doppler imaging. RESULTS: By following ASE recommended criteria, we observed that 12% of patients with AS had mild DD. We also compared single standard Doppler values with normal age-stratified reference values and showed a wide variation in the number of patients with AS outside the 95% confidence interval (CI) of normal values depending on the variable chosen (ranging from 1.1% to 30.5%). CONCLUSIONS: By following recommended criteria, our cross-sectional study shows that DD was infrequent and mild in patients with AS.

Atrial fibrillation prevalence revisited.

BACKGROUND: The estimate of 0.4-1.0% prevalence of atrial fibrillation in the most recent American guidelines is based mainly on studies including patients with permanent atrial fibrillation (AF), although recent evidence shows that the stroke risk is similar with paroxysmal and persistent AF. Our objective was to determine the prevalence of AF in Sweden, irrespective of type and to what extent patients with AF receive adequate stroke prophylaxis. METHOD: Retrospective study of patients with a clinical diagnosis of atrial fibrillation between 2005 and 2010 in the national Swedish Patient Register matched with data from the National Prescribed Drugs Register. RESULTS: We identified 307 476 individuals with a diagnosis of atrial fibrillation. Of these, 209 141 were still alive on the last day of the inclusion period, signifying a prevalence of clinically diagnosed AF in Sweden of 2.9% of the total adult (≥20 years) population. Only 42% of them had purchased an oral anticoagulant within 6 months of the first presentation with AF during the study period. Those at the highest risk of stroke were those least likely to receive anticoagulant treatment. Undertreatment was common amongst women and individuals >80 years, whilst overtreatment was common amongst young men without risk factors. CONCLUSION: The prevalence of atrial fibrillation is at least 2.9% of the Swedish adult population, not counting 'silent atrial fibrillation'. The official US figures probably underestimate the magnitude of the problem by a factor of 3-5. More than 80% had risk factors motivating anticoagulation therapy.

Out-of-hospital cardiac arrest: Causes according to autopsy and electrocardiography - Analysis of 781 patients with neither hospital care nor prescribed medication during the preceding two years.

BACKGROUND: There is a knowledge gap regarding aetiology of and potential for predicting out-of-hospital cardiac arrest (OHCA) among individuals who are healthy before the event. AIM: To describe causes of OHCA and the potential for predicting OHCA in apparently healthy patients. METHODS: Patients were recruited from the Swedish Register of Cardiopulmonary Resuscitation from November 2007 to January 2011. Inclusion criteria were: OHCA with attempted CPR but neither dispensed prescription medication nor hospital care two years before the event The register includes the majority of patients suffering OHCA in Sweden where cardiopulmonary resuscitation (CPR) was attempted. Medication status was defined by linkage to the Swedish Prescribed Drug Register. Cause of death was assessed based on autopsy and the Swedish Cause of Death Register. Prediction of OHCA was attempted based on available electrocardiograms (ECG) before the OHCA event. RESULTS: Altogether 781 individuals (16% women) fulfilled the inclusion criteria. Survival to 30 days was 16%. Autopsy rate was 72%. Based on autopsy, 70% had a cardiovascular aetiology and 59% a cardiac aetiology. An ECG recording before the event was found in 23% of cases. The ECG was abnormal in 22% of them. CONCLUSION: Among OHCA victims who appeared to be healthy prior to the event, the cause was cardiovascular in the great majority according to autopsy findings. A minority had a preceding abnormal ECG that could have been helpful in avoiding the event.

Cardiac repolarization and its relation to ventricular geometry and rate in reverse remodelling during antihypertensive therapy with irbesartan or atenolol: results from the SILVHIA study.

Hypertensive left ventricular (LV) hypertrophy is associated with a substantial risk for malignant arrhythmias and sudden death. According to recent results, antihypertensive therapy with the angiotensin II type 1 receptor blocker irbesartan reverses both structural and electrical remodelling. However, the relation between the LV geometric pattern (concentric vs eccentric) and electrical reverse remodelling has not been characterized, neither has the relation between repolarization and rate (QT/RR and JT/RR relation), which presumably reflects the propensity for bradycardia-dependent ventricular arrhythmia. In this study, repeat echocardiographic and electrocardiographic measurements were performed in hypertensive patients with LV hypertrophy, randomized to double-blind therapy with irbesartan (n = 44) or the beta(1)-adrenoceptor blocker atenolol (n = 48) for 48 weeks; 53 patients had concentric and 39 eccentric LV hypertrophy. In addition, 37 matched hypertensive subjects without LV hypertrophy and no current therapy served as controls. Irbesartan induced structural and electrophysiological reverse remodelling, independent of LV geometry. In contrast, atenolol had similar beneficial effect only in patients with concentric LV hypertrophy, while the response in those with eccentric hypertrophy was unfavourable with both prolonged repolarization time and an increased QT/RR slope (suggesting reverse-use dependence). In conclusion, there is a significant geometry-related difference in the reverse remodelling processes induced by irbesartan and atenolol. Echocardiographic characterization of the geometry in hypertension-induced LV hypertrophy might become an important step in the selection of optimal antihypertensive therapy.

Time-dependent variation in the cardiac conduction system assessed in young healthy individuals at weeks' interval: implications for clinical trials.

The time-dependent physiologic variations of the cardiac conduction system were evaluated at repeated invasive studies in 10 healthy individuals. Their mean age was 28 years (range 22 to 34) and they volunteered to undergo two electrophysiologic studies at intervals of 14 to 63 days (mean 25). The coefficients of variation, repeatability and reproducibility, which should be the preferred statistics when assessing the reproducibility of continuous variables, were calculated. The mean sinus cycle length had a high reproducibility, with coefficients of variation between 2% and 6%. The mean and maximal sinus node recovery times, however, varied considerably. The reproducibility was very high for ventricular depolarization and repolarization (QRS, JT, QT), with coefficients of variation between 2% and 6%. The coefficients of variation were below the acceptable 10% value for intraatrial conduction, atrioventricular (AV) node conduction, His-Purkinje conduction as well as the Wenckebach point; for the effective refractory period of the AV node, it was 12%. Repeat invasive electrophysiologic testing is a safe and reproducible method for evaluating and comparing cardioactive drug effects in healthy subjects. The same statistical analyses were applied to previously published studies on continuous electrophysiologic variables, which allowed comparisons among different groups of healthy and sick persons, as well as among different electrophysiologic variables and procedures. Furthermore, the minimal actual treatment differences that can be detected with a reasonable (80%) probability at a predetermined (5%) significance level using a crossover design were estimated for different electrophysiologic variables. These data will assist in the calculation of the necessary sample size for clinical trials and related purposes.

Diagnostic value of programmed ventricular stimulation in patients with bifascicular block: a prospective study of patients with and without syncope.

OBJECTIVES: The aim of this study was to examine the inducibility of ventricular arrhythmias in patients with bifascicular block both with and without a history of syncope and to relate the findings to clinical events during follow-up. BACKGROUND: Patients with bifascicular block have an increased risk of sudden death that is not reduced by pacemaker treatment. This risk could be related to a high incidence of ventricular arrhythmias. METHOD: Programmed ventricular stimulation was performed in 101 patients with bifascicular block: 41 had a history of unexplained syncope, and 60 were asymptomatic. RESULTS: Programmed ventricular stimulation resulted in a sustained ventricular arrhythmia in 18 patients (18%), 8 in the syncope group and 10 in the nonsyncope group (p = NS). Three patients in each group had an inducible sustained monomorphic ventricular tachycardia. During a mean follow-up of 21 months, 10 patients experienced a clinical event defined as sudden death (n = 4), syncope (n = 5) or appropriate discharges from an implantable cardioverter-defibrillator (n = 1). Only one of these patients had an inducible ventricular arrhythmia at baseline. CONCLUSIONS: The inducibility of ventricular arrhythmias is high in patients with bifascicular block and of the same magnitude in patients with and without a history of syncope. Clinical events during follow-up were not predicted by programmed ventricular stimulation in either of the two groups. The finding of inducible ventricular arrhythmia in patients with bifascicular block should therefore be interpreted with caution.

HLA B27-associated rheumatic diseases with severe cardiac bradyarrhythmias. Clinical features and prevalence in 223 men with permanent pacemakers.

A 15-fold increase in the prevalence of ankylosing spondylitis in a group of 223 men with permanent cardiac pacemakers has recently been demonstrated. In this study of the same patient group, the prevalence of other related rheumatic syndromes was investigated by clinical examination and HLA typing. The clinical picture and electrocardiographic features of all patients with HLA B27-associated rheumatic disease (seronegative spondarthritis) were analyzed. Altogether 28 patients, 12.6 percent (95 percent confidence limits: 8.2 to 17.0 percent), fulfilled inclusion criteria for seronegative spondarthritides; 15 had ankylosing spondylitis. The seronegative spondarthritides previously had been diagnosed in less than 50 percent of the patients. Twenty-two (85 percent) of the 26 HLA-typed patients were B27-positive, implying a very strong association with this genetically determined cell surface protein. Patients with severe bradyarrhythmias associated with the seronegative spondarthritides were thus found to constitute a large proportion of the 223 men with permanent pacemakers. A high frequency of aortic regurgitation and all kinds of bradyarrhythmias were found. Twenty patients had complete heart block--in a majority, occurring intermittently, but otherwise without distinguishing features.

HLA-B27-associated heart disease. Clinicopathologic study of three cases.

The histologic features of the cardiac lesions in HLA-B27-associated heart disease were examined in three cases that illustrate different nuances of the clinical spectrum of this disorder. One of these cases constitutes an important link between the previously established concept of cardiac manifestations in ankylosing spondylitis and Reiter's disease and the recently introduced, wider concept of HLA-B27-associated cardiac manifestations. A correlation between the invasive electrophysiologic results and the autopsy findings is demonstrated in another case.

Ankylosing spondylitis: an important cause of severe disturbances of the cardiac conduction system. Prevalence among 223 pacemaker-treated men.

The cause of severe disturbances of the cardiac conduction system is seldom possible to establish clinically at pacemaker implantation, apart from cases of acute myocardial infarction or digitalis intoxication and in relatively rare cases of inflammatory disorders such as sarcoidosis and systemic sclerosis. Since cardiac manifestations, mainly conduction disturbances, occur in patients with ankylosing spondylitis, the prevalence of this disease was determined using radiologic screening for sacroiliitis in a population of 223 men who had permanently implanted pacemakers. Sacroiliitis was found in 19 men (8.5 percent), 15 of whom fulfilled the diagnostic criteria for ankylosing spondylitis. In six patients, sacroiliitis was asymptomatic and two of the patients were completely free of symptoms other than those originating from their heart manifestations. In seven of the 15 patients with ankylosing spondylitis and in the four patients with sacroiliitis without clinical criteria of ankylosing spondylitis, the diagnosis was previously unknown. Uveitis and aortic regurgitation occurred in five patients each, while peripheral arthritis was twice as common. The prevalence of sacroiliitis and ankylosing spondylitis of 8.5 and 6.7 percent, respectively, differ significantly (p less than 0.01) from the frequencies found in general Caucasian populations of 1 to 2 and 0.1 to 0.5 percent, respectively. HLA B27 was present in more than 80 percent of the patients with sacroiliitis and/or ankylosing spondylitis, compared with 8 to 10 percent in the general population. This strong association is in accordance with previous studies of patients with symptomatic sacroiliitis and/or ankylosing spondylitis. Thus sacroiliitis, diagnosed by x-ray, can be considered a marker for this relatively common rheumatic cause of severe disturbances of the cardiac conduction system.

HLA-B27: an important genetic risk factor for lone aortic regurgitation and severe conduction system abnormalities.

PURPOSE: HLA-B27, an immunogenetic marker that is present in 8 percent of the white population around the world, has been found to be an important risk factor for the development of a group of rheumatic disorders, the seronegative spondyloarthropathies. Our objective was to assess the possible role of HLA-B27 and the associated inflammatory disease process in the development of lone aortic regurgitation. PATIENTS AND METHODS: A group of 91 patients with lone aortic regurgitation were studied by HLA typing and clinical and roentgenologic examination. RESULTS: The HLA-B27-associated inflammatory disease process was found to be the probable underlying cause in 15 to 20 percent of patients with lone aortic regurgitation of different degrees of severity. Furthermore, HLA-B27 was found in 88 percent of the male patients with the combination of aortic regurgitation and severe conduction system abnormalities. CONCLUSION: We suggest that this cardiac syndrome should be regarded as an HLA-B27-associated syndrome, sometimes part of ankylosing spondylitis or Reiter's disease, but just as often presenting without obvious rheumatic disease. The marker is thus an important and widely distributed risk factor not only for the development of rheumatic disease but also for acquired aortic regurgitation and sever conduction system abnormalities.

Myocardial injury after electrical therapy for cardiac arrhythmias assessed by troponin-T release.

Episodes of ventricular fibrillation with subsequent intracardiac, and to a lesser extent, external defibrillation give rise to a statistically significant increase in S-troponin T, S-CK-MB(mass) and S-myoglobin indicative of a minor myocardial injury or dysfunction. In contrast, no such signs were observed after external direct-current conversion of atrial fibrillation using high energies, or after pace-terminated ventricular tachycardia.

Atrioventricular block progression in patients with bifascicular block assessed by repeated electrocardiography and a bradycardia-detecting pacemaker.

Syncope may be due to intermittent high-degree atrioventricular (AV) block, but a cause-relation is sometimes difficult to prove. Diagnostic methods with high predictive value proven by instruments for safe and sensitive follow-up are needed. A bradycardia-detecting pacemaker was used in patients with bifascicular block, who had been the subjects of pharmacologic stress testing of the His-Purkinje system. Thirty-seven patients were included, of whom 26 had experienced at least 1 syncopal episode of suspected bradycardia origin, and 11 had previously documented transient high-degree AV block. The electrophysiologic study included injection of disopyramide 2 mg/kg (up to 150 mg) over 5 minutes. A positive test result was defined as spontaneous or pacing-induced His-Purkinje high-degree AV block after drug or a drug-induced HV prolongation of > or = 50%. Patients were followed an average 63 months with repeated electrocardiography and a diagnostic pacemaker (n = 23). Altogether, 24 patients had a significant bradycardia diagnosed by either or both methods. The sensitivity and positive predictive values were: HV interval > or = 70 ms at baseline, 47% and 88%; a positive disopyramide test result, 75% and 80%; and HV interval > or = 70 ms or a positive disopyramide test result, 93% and 74%, respectively. Thus, the diagnostic pacemaker is a safe and sensitive tool for evaluating the information obtained at electrophysiologic study, and pharmacologic stress testing with disopyramide has an informative value in patients with bifascicular block and syncope when results at baseline are inconclusive.

Incidence of sudden death after radiofrequency ablation of the atrioventricular junction for atrial fibrillation.

This study assesses the incidence of sudden death and classifies the causes of death following radiofrequency ablation of the atrioventricular (AV) junction. We studied 220 patients with paroxysmal (n = 105) or chronic (n = 115) atrial fibrillation (AF) and a mean age of 64 +/- 12 years. These patients were followed 31 +/- 15 months after radiofrequency ablation of the AV junction and pacemaker implantation. In 86 patients, structural heart disease was identified before the procedure. All patients were traced via the Swedish National Civic Registry and Cause of Death Registry. The cause-of-death was classified according to data from death certificates, autopsy protocols, and medical records. Thirty-one patients (mean age 69 +/- 11 years, 16 men) died 15 +/- 15 months (range 0.2 to 60) after the procedure. There were 6 sudden unexplained deaths, 14 cardiovascular deaths, and 11 deaths from noncardiovascular causes. Eleven patients, all with structural heart disease, died suddenly out of hospital 16 +/- 16 months (range 0.2 to 42) after the procedure. In 6 of these there was no obvious cause of death. Three of these 6 patients underwent autopsy, which showed extensive coronary artery disease (n = 1), severe heart failure (n = 1) and cardiac hypertrophy and dilation (n = 1). The remaining 3 all had depressed left ventricular systolic function and a history of congestive heart failure. Five of the patients who died suddenly from cardiovascular causes had autopsies that revealed acute myocardial infarction (n = 4) and massive pulmonary embolism (n = 1).

Frequency and long term follow up of valvar insufficiency caused by retrograde aortic radiofrequency catheter ablation procedures.

OBJECTIVE: To assess the frequency of valvar complications caused by left sided radiofrequency catheter ablation using the retrograde aortic technique. METHODS: 179 patients (118 male) with a mean (SD) age of 43 (17) years underwent 216 procedures at one centre. The target of the ablation was an accessory atrioventricular pathway in 144 patients, the atrioventricular junction in 29 patients, and a ventricular tachycardia in six patients. In 25 patients structural heart disease was identified before the procedure (ischaemic heart disease 10, cardiomyopathy nine, valvar three, other three). Echo/Doppler examinations were performed the day before the procedure and within 24 hours postablation; the investigations were all reviewed by the same investigator. Patients with identified valvar injury caused by the procedure were followed for 42 (7) months. RESULTS: Valvar injury caused by the ablation procedure was identified in four young (age 30 (8) years), otherwise healthy patients with left lateral atrioventricular accessory pathways. Mild mitral insufficiency with a central regurgitation jet was detected in two patients and remained unchanged at follow up. Mild aortic insufficiency was detected in another two patients. In one of these the regurgitation jet was central and remained unchanged at follow up. In one patient the regurgitation jet was located between the non-coronary and left cusps in relation to a loosely attached structure. Both the structure and the valvar regurgitation disappeared during follow up. No clinical complications occurred in any of the patients during follow up. CONCLUSION: In this study, the frequency of valvar complications after left sided radiofrequency catheter ablation using the retrograde aortic technique was 1.9%.

Carbamazepine induced bradycardia--a problem in general or only in susceptible patients? A 24-h long-term electrocardiogram study.

Carbamazepine is a first line drug in the treatment of epilepsy and trigeminal neuralgia, but may exert negative chronotropic and dromotropic effects on the cardiac conduction system. Bradyarrhythmias of different types and severity have been described, especially in the elderly, but the prevalence of arrhythmias in a larger group of carbamazepine treated patients is unknown. Forty-eight patients, 40 years of older, on continuous carbamazepine treatment because of various neurologic disorders were investigated by interview, physical examination, 12-lead surface electrocardiogram, and 24-h long-term electrocardiogram recording. The prevalence of bradyarrhythmias was compared with that in an age-stratified reference group. There was no differences between the two groups, either in the number or the duration of pauses or in the type of pauses. In conclusion, carbamazepine does not increase the risk of bradyarrhythmias in the vast majority of patients.

Magnetocardiographic localization of arrhythmia substrates: a methodology study with accessory pathway ablation as reference.

In magnetocardiographic (MCG) localization of arrhythmia substrates, a model of the thorax as volume conductor is a crucial component of the calculations. In this study, we investigated different models of the thorax, to determine the most suitable to use in the computations. Our methods and results are as follows. We studied 11 patients with overt Wolff-Parkinson-White syndrome, scheduled for catheter ablation. The MCG registrations were made with a 37-channel "superconducting quantum interference device" system. The underlying equivalent current dipole was computed for the delta-wave. Three models of the thorax were used: the infinite halfspace, a sphere and a box. For anatomical correlation and to define the suitable sphere and box, magnetic resonance images were obtained. As reference we used the position of the tip of the catheter, at successful radio-frequency-ablation, documented by cine-fluoroscopy. Nine patients could be evaluated. The mean errors (range) when using the infinite halfspace, the sphere and the box were 96 (49-125), 21 (5-39), and 36 mm (20-58 mm), respectively (p < 0.0001). In conclusion, the sphere was significantly better suited than the other models tested in this study, but even with this model the accuracy of MCG localization must further improve to be clinically useful. More realistic models of the thorax are probably required to achieve this goal.

Changes in arrhythmia profile and heart rate variability during abrupt withdrawal of antiepileptic drugs. Implications for sudden death.

Sudden unexpected death (SUD) has been associated with low or undetectable concentrations of antiepileptic drugs in patients with epilepsy suggesting that a sudden fall in plasma levels of these drugs might be a critical factor for the occurrence of SUD. We studied the changes in arrhythmia profile and heart-rate variability, during abrupt withdrawal of carbamazepine and phenytoin treatment in 10 patients with side effects on these drugs. Continuous ECG recording and daily measurements of drug plasma concentrations were performed from the last day of steady-state treatment and the following 4 days. Three patients had a 10-fold increase in ventricular premature beats. In addition, there was a significant reduction in heart-rate variability, assessed over 24 hours, in both the time (SDNN index, P = 0.03) and frequency domains from days 1-5. In the frequency domain analysis there was a significant reduction in total power (P = 0.01), very-low-frequency power (P = 0.004) and in low-frequency (LF) power (P = 0.01). Similar reductions in heart-rate variability and increases in ventricular automaticity have been associated with increased mortality in other patient groups. Two factors that might contribute to the increased rate of SUD in patients with epilepsy have thus been identified.

Prevalence of cardiac conduction disturbances during carbamazepine treatment: preliminary data.

Twenty-five epileptic patients chronically treated with carbamazepine underwent 24 h electrocardiogram (ECG) monitoring in order to evaluate the prevalence of cardiac conduction abnormalities. Plasma levels of carbamazepine and its metabolite, carbamazepine-10,11-epoxide, were determined by liquid chromatography. Six patients had mild ECG abnormalities. These patients did not differ from the others with respect to plasma concentrations of the drug and its metabolite.