The effects of P2Y12 adenosine receptors' inhibitors on central and peripheral chemoreflexes

Introduction: The most common side effect of ticagrelor is dyspnea, which leads to premature withdrawal of this life-saving medication in 6.5% of patients. Increased chemoreceptors' sensitivity was suggested as a possible pathophysiological explanation of this phenomenon; however, the link between oversensitization of peripheral and/or central chemosensory areas and ticagrelor intake has not been conclusively proved. Methods: We measured peripheral chemoreceptors' sensitivity using hypoxic ventilatory response (HVR), central chemoreceptors' sensitivity using hypercapnic hyperoxic ventilatory response (HCVR), and dyspnea severity before and 4 ± 1 weeks following ticagrelor initiation in 11 subjects with chronic coronary syndrome undergoing percutaneous coronary intervention (PCI). The same tests were performed in 11 age-, sex-, and BMI-matched patients treated with clopidogrel. The study is registered at ClinicalTrials.com at NCT05080478. Results: Ticagrelor significantly increased both HVR (0.52 ± 0.46 vs. 0.84 ± 0.69 L min-1 %-1; p < 0.01) and HCVR (1.05 ± 0.64 vs. 1.75 ± 1.04 L min-1 mmHg-1; p < 0.01). The absolute change in HVR correlated with the change in HCVR. Clopidogrel administration did not significantly influence HVR (0.63 ± 0.32 vs. 0.58 ± 0.33 L min-1%-1; p = 0.53) and HCVR (1.22 ± 0.67 vs. 1.2 ± 0.64 L min-1 mmHg-1; p = 0.79). Drug-related dyspnea was reported by three subjects in the ticagrelor group and by none in the clopidogrel group. These patients were characterized by either high baseline HVR and HCVR or excessive increase in HVR following ticagrelor initiation. Discussion: Ticagrelor, contrary to clopidogrel, sensitizes both peripheral and central facets of chemodetection. Two potential mechanisms of ticagrelor-induced dyspnea have been identified: 1) high baseline HVR and HCVR or 2) excessive increase in HVR or HVR and HCVR. Whether other patterns of changes in chemosensitivities play a role in the pathogenesis of this phenomenon needs to be further investigated.

Low-dose dopamine improves ventilatory efficiency during exercise in heart failure with preserved ejection fraction through inhibition of tonic activity of peripheral chemoreceptors

Introduction

Peripheral chemoreceptors (PChRs) play an important role in adequate oxygenation by 1) maintaining baseline ventilation (tonic activity) and 2) providing hyperventilation in response to acute hypoxia (reflexia). It has been previously shown that in patients with heart failure with reduced ejection fraction hypertonicity and/or hyperreflexia of PChRs contribute to exercise intolerance (ExIn). It is unknown whether similar mechanisms are present in heart failure with preserved ejection fraction (HFpEF) and which component of PChR functionality has a decisive role in this matter.

Purpose

The aim of this study was to evaluate the role of PChRs in ExIn in patients with HFpEF.

Methods

All patients underwent assessment of PChRs which included measurements of: 1) tonic activity (TA, decrease in ventilation following pharmacological inhibition of PChRs), 2) reflex response (RR; an increase in ventilation in the response to acute hypoxia). The inhibition of PChRs was achieved with low-dose dopamine infusion (3 μg kg–1 min–1) and the acute hypoxia was produced with brief nitrogen gas administrations. Enrolled patients underwent symptom-limited cardiopulmonary exercise test using cycle ergometer from which peak oxygen consumption (peakVO2) and the slope relating ventilation to carbon dioxide (VE/VCO2 slope) were derived. All measurements (including PChRs' function tests and cardiopulmonary exercise test) were performed twice in a randomized, double-blinded and placebo-controlled manner (dopamine vs normal saline).

Results

We included 12 stable patients with HFpEF (age: 73±7 years, LVEF: 58±3%). During exercise the inhibition of PChRs with dopamine resulted in the improvement (decrease) in VE/VCO2 slope comparing to placebo (36±3.6 vs 34.3±3.7, p=0.04) but no change regarding peakVO2. There was a correlation between TA and relative magnitude of improvement in VE/VCO2 following PChRs inhibition (R=0.76, p=0.005). We also found a trend for correlation between RR and VE/VCO2 measured during placebo (R=0.56, p=0.059). There was no correlation between TA and RR (p=0.24).

Conclusion

Both TA and RR of PChRs are involved in ventilatory inefficacy during exercise in HFpEF – but in different ways. While augmented RR is likely an indicator of high VE/VCO2, the elevated TA indicates the magnitude of the improvement in exercise tolerance following PChRs deactivation. Thus, further interventions aimed at the modulation of PChRs should enroll patients based on TA rather than RR.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Science Centre, PRELUDIUM grant

Inhibition of peripheral chemoreceptors improves ventilatory efficiency during exercise in heart failure with preserved ejection fraction − a role of tonic activity and acute reflex response

Peripheral chemoreceptors (PChRs) play a significant role in maintaining adequate oxygenation in the bloodstream. PChRs functionality comprises two components: tonic activity (PChT) which regulates ventilation during normoxia and acute reflex response (peripheral chemosensitivity, PChS), which increases ventilation following a specific stimulus. There is a clear link between augmented PChS and exercise intolerance in patients with heart failure with reduced ejection fraction. It has been also shown that inhibition of PChRs leads to the improvement in exercise capacity. However, it has not been established yet: 1) whether similar mechanisms take part in heart failure with preserved ejection fraction (HFpEF) and 2) which component of PChRs functionality (PChT vs. PChS) is responsible for the benefit seen after the acute experimental blockade. To answer those questions we enrolled 12 stable patients with HFpEF. All participants underwent an assessment of PChT (attenuation of minute ventilation in response to low-dose dopamine infusion), PChS (enhancement of minute ventilation in response to hypoxia) and a symptom-limited cardiopulmonary exercise test on cycle ergometer. All tests were placebo-controlled, double-blinded and performed in a randomized order. Under resting conditions and at normoxia dopamine attenuated minute ventilation and systemic vascular resistance (p = 0.03 for both). These changes were not seen with placebo. Dopamine also decreased ventilatory and mean arterial pressure responses to hypoxia (p < 0.05 for both). Inhibition of PChRs led to a decrease in V˙E/V˙CO₂ comparing to placebo (36 ± 3.6 vs. 34.3 ± 3.7, p = 0.04), with no effect on peak oxygen consumption. We found a significant relationship between PChT and the relative decrement of V˙E/V˙CO₂ on dopamine comparing to placebo (R = 0.76, p = 0.005). There was a trend for correlation between PChS (on placebo) and V˙E/V˙CO₂ during placebo infusion (R = 0.56, p = 0.059), but the relative improvement in V˙E/V˙CO₂ was not related to the change in PChS (dopamine vs. placebo). We did not find a significant relationship between PChT and PChS. In conclusion, inhibition of PChRs in HFpEF population improves ventilatory efficiency during exercise. Increased PChS is associated with worse (higher) V˙E/V˙CO₂, whereas PChT predicts an improvement in V˙E/V˙CO₂ after PChRs inhibition. This results may be meaningful for patient selection in further clinical trials involving PChRs modulation.

Induction of Day-Time Periodic Breathing is Associated With Augmented Reflex Response From Peripheral Chemoreceptors in Male Patients With Systolic Heart Failure

Spontaneous day-time periodic breathing (sPB) constitutes a common phenomenon in systolic heart failure (HF). However, it is unclear whether PB during wakefulness could be easily induced and what are the physiological and clinical correlates of patients with HF in whom PB induction is possible. Fifty male HF patients (age 60.8 ± 9.8 years, left ventricle ejection fraction 28.0 ± 7.4%) were prospectively screened and 46 enrolled. After exclusion of patients with sPB the remaining underwent trial of PB induction using mild hypoxia (stepwise addition of nitrogen gas to breathing mixture) which resulted in identification of inducible (iPB) in 51%. All patients underwent assessment of hypoxic ventilatory response (HVR) using transient hypoxia and of hypercapnic ventilatory response (HCVR) employing Read’s rebreathing method. The induction trial did not result in any adverse events and minimal SpO₂ during nitrogen administration was ∼85%. The iPB group (vs. non-inducible PB group, nPB) was characterized by greater HVR (0.90 ± 0.47 vs. 0.50 ± 0.26 L/min/%; p <0.05) but comparable HCVR (0.88 ± 0.54 vs. 0.67 ± 0.68 L/min/mmHg; p = NS) and by worse clinical and neurohormonal profile. Mean SpO₂ which induced first cycle of PB was 88.9 ± 3.7%, while in sPB mean SpO₂ preceding first spontaneous cycle of PB was 96.0 ± 2.5%. There was a reverse relationship between HVR and the relative variation of SpO₂ during induced PB (r = −0.49, p = 0.04). In summary, PB induction is feasible and safe in HF population using simple and standardized protocol employing incremental, mild hypoxia. Pathophysiology of iPB differs from sPB, as it relies mostly on overactive peripheral chemoreceptors. At the same time enhanced HVR might play a protective role against profound hypoxia during iPB.

Contribution of Peripheral Chemoreceptors to Exercise Intolerance in Heart Failure

Peripheral chemoreceptors (PChRs), because of their strategic localization at the bifurcation of the common carotid artery and along the aortic arch, play an important protective role against hypoxia. Stimulation of PChRs evokes hyperventilation and hypertension to maintain adequate oxygenation of critical organs. A relationship between increased sensitivity of PChRs (hyperreflexia) and exercise intolerance (ExIn) in patients with heart failure (HF) has been previously reported. Moreover, some studies employing an acute blockade of PChRs (e.g., using oxygen or opioids) demonstrated improvement in exercise capacity, suggesting that hypertonicity is also involved in the development of ExIn in HF. Nonetheless, the precise mechanisms linking dysfunctional PChRs to ExIn remain unclear. From the clinical perspective, there are two main factors limiting exercise capacity in HF patients: subjective perception of dyspnoea and muscle fatigue. Both have many determinants that might be influenced by abnormal signalling from PChRs, including: exertional hyperventilation, oscillatory ventilation, ergoreceptor oversensitivity, and augmented sympathetic tone. The latter results in reduced muscle perfusion and altered muscle structure. In this review, we intend to present the milieu of abnormalities tied to malfunctioning PChRs and discuss their role in the complex relationships leading, ultimately, to ExIn.

Acute hyperoxia reveals tonic influence of peripheral chemoreceptors on systemic vascular resistance in heart failure patients

Peripheral chemoreceptors’ (PCh) hyperactivity increases sympathetic tone. An augmented acute ventilatory response to hypoxia, being a marker of PCh oversensitivity, was also identified as a marker of poor prognosis in HF. However, not much is known about the tonic (chronic) influence of PCh on cardio-respiratory parameters. In our study 30 HF patients and 30 healthy individuals were exposed to 100% oxygen for 1 min during which minute ventilation and hemodynamic parameters were non-invasively recorded. Systemic vascular resistance (SVR) and mean arterial pressure (MAP) responses to acute hyperoxia differed substantially between HF and control. In HF hyperoxia caused a significant drop in SVR in early stages with subsequent normalization, while increase in SVR was observed in controls. MAP increased in controls, but remained unchanged in HF. Bilateral carotid bodies excision performed in two HF subjects changed the response to hyperoxia towards the course seen in healthy individuals. These differences may be explained by the domination of early vascular reaction to hyperoxia in HF by vasodilation due to the inhibition of augmented tonic activity of PCh. Otherwise, in healthy subjects the vasoconstrictive action of oxygen remains unopposed. The magnitude of SVR change during acute hyperoxia may be used as a novel method for tonic PCh activity assessment.

Pathophysiology of Advanced Heart Failure: What Knowledge Is Needed for Clinical Management?

Understanding of heart failure (HF) has evolved from a simple hemodynamic problem through a neurohormonally and proinflammatory-driven syndrome to a complex multiorgan dysfunction accompanied by inadequate energy handling. This article discusses the most important clinical aspects of advanced HF pathophysiology. It presents the concept of neurohormonal activation and its deleterious effect on cardiovascular system and reflex control. The current theories regarding the role of inflammation, cytokine activation, and myocardial remodeling in HF progression are presented. Advanced HF is a multiorgan syndrome with interplay between cardiovascular system and other organs. The role of iron deficiency is also discussed.

Frailty and cognitive impairment are predictive of takotsubo syndrome following pacemaker implantation

BACKGROUND

Pacemaker (PM) implantation may cause acute emotional distress leading to takotsubo syndrome (TTS). Frailty and cognitive impairment are known to influence outcomes after surgical procedures. It is unclear whether they may also predispose to TTS following PM implantation.

METHODS

We identified nine cases (81 ± 6 years) of TTS following PM implantation that took place between 2013 and 2017 in one high volume implantation center. TTS was diagnosed based on typical echocardiographic appearance with resolution over time and (in cases where deemed necessary) normal coronary angiography. The TTS cases were compared with 30 consecutive cases of PM implantation (75 ± 9 years), which were not complicated by TTS (control group). Frailty was assessed using retrospective Risk Analysis Index (RAI-A). Pacing parameters were analyzed during PM implantation and after 1 month.

RESULTS

Cognitive impairment was more prevalent (67% vs 10%, P = .0005), and RAI-A index was significantly higher in the TTS group compared to the control group (26 ± 13.7 vs 13.1 ± 9.8, P = .008). Perioperative right ventricular threshold was significantly higher in patients with TTS comparing to controls (0.99 ± 0.43 V vs 0.74 ± 0.20 V, P = .04). The magnitude of decrease in right ventricular threshold between implantation and 1 month follow-up was greater in TTS patients compared to controls (-0.41 ± 0.29 V vs -0.15 ± 0.38 V, P = .049).

CONCLUSIONS

TTS is a rare complication of PM implantation. Patients with cognitive impairment and frailty are at risk of TTS. Right ventricular pacing threshold is acutely affected by TTS and improves over time.

Effectiveness of screening for atrial fibrillation and its determinants. A meta-analysis

Background

Many atrial fibrillation patients eligible for oral anticoagulants are unaware of the presence of AF, and improved detection is necessary to facilitate thromboprophylaxis against stroke.

Objective

To assess the effectiveness of screening for AF compared to no screening and to compare efficacy outcomes of different screening strategies.

Materials and methods

Cochrane Central Register of Controlled Trials, EMBASE and MEDLINE from Jan 1, 2000 –Dec 31, 2015 were searched. Studies employing systematic or opportunistic screening and using ECG or pulse palpation in populations age ≥40 years were included. Data describing study and patient characteristics and number of patients with new AF were extracted. The outcome was the incidence of previously undiagnosed AF.

Results

We identified 25 unique (3 RCTs and 22 observational) studies (n = 88 786) from 14 countries. The incidence of newly detected AF due to screening was 1.5% (95% CI 1.1 to 1.8%). Systematic screening was more effective than opportunistic: 1.8% (95% CI 1.4 to 2.3%) vs. 1.1% (95% CI 0.6 to 1.6%), p<0.05, GP-led screening than community based: 1.9% (95% CI 1.4 to 2.4%) vs. 1.1% (95% CI 0.7 to 1.6%), p<0.05, and repeated heart rhythm measurements than isolated assessments of rhythm: 2.1% (95% CI 1.5–2.8) vs. 1.2% (95% CI 0.8–1.6), p<0.05. Only heart rhythm measurement frequency had statistical significance in a multivariate meta-regression model (p<0.05).

Conclusions

Active screening for AF, whether systematic or opportunistic, is effective beginning from 40 years of age. The organisation of screening process may be more important than technical solutions used for heart rhythm assessment.

Seat belts-related behaviors in car drivers with cardiac implantable electronic devices

BACKGROUND

Seat belt use is the single most effective means of reducing fatal injuries in road traffic accidents. The presence of a cardiac implantable electronic device (CIED) might influence seat belt-related behaviors due to the physical proximity of the seat belt and left subclavian area in which the device is usually implanted. Understanding the underlying mechanisms of improper seat belt use may improve safety of these patients.

METHODS

We performed a prospective study using a structured questionnaire with 120 CIED recipients (age, 63.9 ± 10.9 years) attending a pacing outpatient clinic. All study participants were active drivers and predominantly male. The majority of patients (79%) had undergone high-energy device implantation.

RESULTS

We found that 18% of study participants do not fasten seat belts on a regular basis or use the seat belt in an atypical fashion (such as under the armpit). Moderate or high level of discomfort from the interaction between seat belt and CIED was present in 27%, while more than half (51%) were afraid of seat belt-induced CIED damage. In multifactorial analysis, we found the following independent predictors of improper seat belt use: (1) at least moderate level of discomfort at the CIED site (P = 0.02); (2) fear of CIED damage (P = 0.009); and (3) irregular seat belt use prior to CIED implantation (P = 0.037).

CONCLUSIONS

Improper seat belt-related behaviors are common in CIED recipients. They arise from previous habits and from CIED-related physical and psychological factors. Patients' education regarding the importance and safety of proper seat belt use is a priority.

Effects of selective carotid body stimulation with adenosine in conscious humans

KEY POINTS

In humans, excitation of peripheral chemoreceptors with systemic hypoxia causes hyperventilation, hypertension and tachycardia. However, the contribution of particular chemosensory areas (carotid vs. aortic bodies) to this response is unclear. We showed that selective stimulation of the carotid body by the injection of adenosine into the carotid artery causes a dose-dependent increase in minute ventilation and blood pressure with a concomitant decrease in heart rate in conscious humans. The ventilatory response was abolished and the haemodynamic response was diminished following carotid body ablation. We found that the magnitude of adenosine evoked responses in minute ventilation and blood pressure was analogous to the responses evoked by hypoxia. By contrast, opposing heart rate responses were evoked by adenosine (bradycardia) vs. hypoxia (tachycardia). Intra-carotid adenosine administration may provide a novel method for perioperative assessment of the effectiveness of carotid body ablation, which has been recently proposed as a treatment strategy for sympathetically-mediated diseases.

ABSTRACT

Stimulation of peripheral chemoreceptors by acute hypoxia causes an increase in minute ventilation (VI), heart rate (HR) and arterial blood pressure (BP). However, the contribution of particular chemosensory areas, such as carotid (CB) vs. aortic bodies, to this response in humans remains unknown. We performed a blinded, randomized and placebo-controlled study in 11 conscious patients (nine men, two women) undergoing common carotid artery angiography. Doses of adenosine ranging from 4 to 512 μg or placebo solution of a matching volume were administered in randomized order via a diagnostic catheter located in a common carotid artery. Separately, ventilatory and haemodynamic responses to systemic hypoxia were also assessed. Direct excitation of a CB with intra-arterial adenosine increased VI, systolic BP, mean BP and decreased HR. No responses in these variables were seen after injections of placebo. The magnitude of the ventilatory and haemodynamic responses depended on both the dose of adenosine used and on the level of chemosensitivity as determined by the ventilatory response to hypoxia. Percutaneous radiofrequency ablation of the CB abolished the adenosine evoked respiratory response and partially depressed the cardiovascular response in one participant. The results of the present study confirm the excitatory role of purines in CB physiology in humans and suggest that adenosine may be used for selective stimulation and assessment of CB activity. The trial is registered at ClinicalTrials.gov NCT01939912.

Carotid body modulation in systolic heart failure from the clinical perspective

Augmented sensitivity of peripheral chemoreceptors (PChS) is a common finding in systolic heart failure (HF). It is related to lower left ventricle systolic function, higher plasma concentrations of natriuretic peptides, worse exercise tolerance and greater prevalence of atrial fibrillation compared to patients with normal PChS. The magnitude of ventilatory response to the activation of peripheral chemoreceptors is proportional to the level of heart rate (tachycardia) and blood pressure (hypertension) responses. All these responses can be measured non-invasively in a safe and reproducible fashion using different methods employing either hypoxia or hypercapnia. Current interventions aimed at modulation of peripheral chemoreceptors in HF are focused on carotid bodies (CBs). There is a clear link between afferent signalling from CBs and sympathetic overactivity, which remains the priority target of modern HF treatment. However, CB modulation therapies may face several potential obstacles: (1) As evidenced by HF trials, an excessive inhibition of sympathetic system may be harmful. (2) Proximity of critical anatomical structures (important vessels and nerves) makes surgical and transcutaneous interventions on CB technically demanding. (3) Co-existence of atherosclerosis in the area of carotid artery bifurcation increases the risk of central embolic events related to CB modulation. (4) The relative contribution of CBs vs. aortic bodies to sympathetic activation in HF patients is unclear. (5) Choosing optimal candidates for CB modulation from the population of HF patients may be problematic. (6) There is a risk of nocturnal hypoxia following CB ablation - mostly after bilateral procedures and in patients with concomitant obstructive sleep apnoea.

Late Cardiac Tamponade as a Result of Parietal Pericardium Erosion

Late onset cardiac tamponade is a rare and particularly challenging (both from diagnostic and management perspectives) complication of intracardiac lead implantation. We present a case of a late tamponade leading to cardiogenic shock, which occurred 1,164 days after implantable cardioverter-defibrillator (ICD) implantation. Open repair revealed unusual and, to our knowledge, not yet reported mechanism of the disease. A pressure sore caused by an ICD lead was found in the parietal layer of pericardium with no visible damage to the visceral layer. Conservative management in the described clinical scenario could be fatal, thus awareness of this pathomechanism of tamponade is critical.

Consequences of peripheral chemoreflex inhibition with low-dose dopamine in humans

Low-dose dopamine inhibits peripheral chemoreceptors and attenuates the hypoxic ventilatory response (HVR) in humans. However, it is unknown: (1) whether it also modulates the haemodynamic reactions to acute hypoxia, (2) whether it also modulates cardiac baroreflex sensitivity (BRS) and (3) if there is any effect of dopamine withdrawal. We performed a double-blind, placebo-controlled study on 11 healthy male volunteers. At sea level over 2 days every subject was administered low-dose dopamine (2 μg kg(-1) min(-1)) or saline infusion, during which we assessed both ventilatory and haemodynamic responses to acute hypoxia. Separately, we evaluated effects of initiation and withdrawal of each infusion and BRS. The initiation of dopamine infusion did not affect minute ventilation (MV) or mean blood pressure (MAP), but increased both heart rate (HR) and cardiac output. Concomitantly, it decreased systemic vascular resistance. Dopamine blunted the ventilatory, MAP and HR reactions (hypertension, tachycardia) to acute hypoxia. Dopamine attenuated cardiac BRS to falling blood pressure. Dopamine withdrawal evoked an increase in MV. The magnitude of the increment in MV due to dopamine withdrawal correlated with the size of the HVR and depended on the duration of dopamine administration. The ventilatory reaction to dopamine withdrawal constitutes a novel index of peripheral chemoreceptor function.

Dissociation between blood pressure and heart rate response to hypoxia after bilateral carotid body removal in men with systolic heart failure

While the ventilatory response to hypoxia is known to be mediated by the carotid bodies, the origin of the haemodynamic alterations evoked by hypoxia is less certain. Bilateral carotid body removal (CBR) performed to treat congestive heart failure may serve as a model to improve our understanding of haemodynamic responses to hypoxia in humans. We studied six congestive heart failure patients before and 1 month after CBR [median (interquartile range): age, 58.5 (56-61) years old; and ejection fraction, 32 (25-34)%]. Peripheral chemosensitivity (hypoxic ventilatory response) was equated to the slope relating lowest oxygen saturation to highest minute ventilation following exposures to hypoxia. Likewise, systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) slopes were calculated as slopes relating the lowest oxygen saturations to the highest SBP, DBP and HR responses. We found that CBR reduces the hypoxic ventilatory response (91%, P < 0.05), SBP (71%, P < 0.05) and DBP slopes (59%, P = 0.07). In contrast, the HR slope remained unchanged. The dissociation between the blood pressure and HR responses after CBR shows involvement of a different chemoreceptive site(s) maintaining the response to acute hypoxia. We conclude that carotid bodies are responsible for ventilatory and blood pressure responses, while the HR response might be mediated by the aortic bodies. The significant reduction of the blood pressure response to hypoxia after CBR suggests a decrease in sympathetic tone, which is of particular clinical relevance in congestive heart failure.

CYP2D6 extensive, intermediate, and poor phenotypes and genotypes in a Polish population

OBJECTIVE

This study investigated the distribution of the CYP2D6 genotypes and phenotypes in a Polish population and compared the concordance of the two methods.

METHODS

Six hundred unrelated healthy individuals from southwestern Poland were studied. The CYP2D6 phenotype was analyzed in 300 individuals using sparteine as a model drug. The CYP2D6 genotype was analyzed in 300 individuals by polymerase chain reaction amplification and restriction fragment length polymorphism techniques for the CYP2D6*1, CYP2D6*3, and CYP2D6*4 alleles. Additionally, in 60 randomly selected healthy individuals both the CYP2D6 phenotype and genotype was assessed to determine accordance between the methods.

RESULTS

Of 300 participants in the study 25 (8.3%) were classified as poor metabolizers, 44 (14.7%) as intermediate metabolizers, and 231 (77%) as extensive metabolizers of sparteine. The frequency of CYP2D6*1, CYP2D6*3, and CYP2D6*4 alleles among the genotyped 300 persons was 75.7%, 1.3%, and 23.0%, respectively. The frequency of CYP2D6 deficient genotypes in a Polish population (8.0%) was similar to phenotyping results. The comparison of phenotype and genotype in 60 randomly selected individuals showed a good concordance of the obtained results. CONCLUSIONS. The frequencies of poor metabolizers for CYP2D6 phenotype (8.3%) and genotype (8.0%) in a Polish population from the southwestern region are in concordance and compare well with most results of poor oxidation metabolizers in other white populations.

The influence of CYP2D6 polymorphism on the antiarrhythmic efficacy of propafenone in patients with paroxysmal atrial fibrillation during 3 months propafenone prophylactic treatment

OBJECTIVE

Propafenone (PPF) is an antiarrhythmic, Class Ic agent. Its metabolism is genetically controlled by a cytochrome P450 isoenzyme named CYP2D6, which shows polymorphism in human population. The aim of this paper was to determine the correlation between the antiarrhythmic efficacy of PPF and the oxidation phenotype. SUBJECTS AND MATERIAL: The study group consisted of 42 patients, aged 36 to 75 years, suffering from paroxysmal atrial fibrillation (AF). The oxidation phenotype was described by the metabolic ratio (MR) of sparteine. The MR value separated the group of poor metabolizers (MR > 20) from the group of extensive metabolizers (MR < 20) with the subgroup of very extensive metabolizers (MR < 1).

METHOD

The study was conducted during a 3-month PPF therapy for the prophylaxis of paroxysmal atrial fibrillation. PPF was given orally, 300-450 mg/day. The oxidation phenotype was checked prior to the administration of PPF. Serum concentration of PPF at 7, 11 days and the end of PPF therapy were determined. Statistical analysis of data was performed with the chi2 test and the Pearson's correlation methods.

RESULTS

In the group of 42 patients, PPF therapy was 100% effective in poor metabolizers (PM). In extensive metabolizers (EM), 61% efficacy was observed with efficacy 0% in very extensive metabolizers (VEM). The correlation between oxidation phenotype and the ability to maintain sinus rhythm (SR) was statistically significant (r = 0.414, p < 0.05).

CONCLUSIONS

The antiarrhythmic efficacy of propafenone depends on the oxidation phenotype; 100% efficacy occurred in the group of poor metabolizers whereas PPF, at the dose tested, was ineffective in very extensive metabolizers.