Abrupt Increase In Heart Rate Research Articles

The effects of expected and unexpected stress on inappropriate aggression in simulated police interventions

Here we performed a before-after ABA-design study in police cadets (N = 82) to compare the effects of unexpected (event-triggered) and expected (anticipatory) stressors on aggression. On the first day of the study, participants filled in the Buss-Perry Aggression Questionnaire (BPAQ) and the Barratt Impulsiveness Scale (BIS) and were fitted with heart rate (HR) monitors, which remained attached till the end of the study. On day 2, they were instructed to perform a police intervention in a realistic training environment. The intervention was preceded either by a warning or by a reassuring audio recording that forecasted violent or routine interventions, respectively. Both groups encountered hostile suspects at the intervention site, the behavior of which, however, did not justify the use of force e.g., aggression. The warning resulted in a gradually developing anticipatory stress as shown by HRs. Cadets exposed to the reassuring audio recording showed minimal anticipatory stress but responded to the hostile suspects by an abrupt increase in HRs, which was missing in the warned group. The magnitude of HR responses was similar in the two groups, only their temporal evolution differed. Although aggression showed some associations with BPAQ and BIS scores, the main predictors of behavior were HR changes according to a Multiple Regression analysis. The gradually developing anticipatory stress was associated with low, whereas the abrupt increase in HRs was associated with high aggression. Our findings suggest that the anticipation of a stressful event improves behavioral control whereas an unexpected stress strongly promotes aggression.

The Impact of Surrounding Road Objects and Conditions on Drivers Abrupt Heart Rate Changes

Recent studies have pointed out the importance of mitigating drivers' stress and negative emotions. These studies show that certain road objects such as big vehicles might be associated with higher stress levels based on drivers' subjective stress measures. Additionally, research shows strong correlations between drivers' stress levels and increased heart rate (HR). In this paper, based on a naturalistic multimodal driving dataset, we analyze the visual scenes of driving in the vicinity of abrupt increases in drivers' HR for the presence of certain stress-inducing road objects. We show that the probability of the presence of such objects increases when becoming closer to the abrupt increase in drivers' HR. Additionally, we show that drivers' facial engagement changes significantly in the vicinity of abrupt increases in HR. Our results lay the ground for a human-centered driving experience by detecting and mitigating drivers' stress levels in the wild.

Continuous heart rate dynamics preceding in-hospital pulseless electrical activity or asystolic cardiac arrest of respiratory etiology

IntroductionRespiratory failure is a common cause of pulseless electrical activity (PEA) and asystolic cardiac arrest, but the changes in heart rate (HR) pre-arrest are not well described. We describe HR dynamics prior to in-hospital cardiac arrest (IHCA) among PEA/asystole arrest patients with respiratory etiology. MethodsIn this retrospective study, we evaluated 139 patients with 3–24 hours of continuous electrocardiogram data recorded preceding PEA/asystole IHCA from 2010-2017. We identified respiratory failure cases by chart review and evaluated electrocardiogram data to identify patterns of HR changes, sinus bradycardia or sinus arrest, escape rhythms, and development right ventricular strain prior to IHCA. ResultsA higher proportion of respiratory cases (58/73, 79 %) fit a model of HR response characterized by tachycardia followed by rapid HR decrease prior to arrest, compared to non-respiratory cases (30/66, 45 %, p < 0.001). Among the 58 respiratory cases fitting this model, 36 (62 %) had abrupt increase in HR occurring 64 (IQR 23–191) minutes prior to arrest, while 22 (38 %) had stable tachycardia until time of HR decrease. Mean peak HR was 123 ± 21 bpm. HR decrease occurred 3.0 (IQR 2.0–7.0) minutes prior to arrest. Sinus arrest occurred during the bradycardic phase in 42/58 of cases; escape rhythms were present in all but 2/42 (5 %) cases. Right ventricular strain ECG pattern, when present, occurred at a median of 2.2 (IQR −0.05–17) minutes prior to onset of HR decrease. ConclusionIHCAs of respiratory etiology follow a model of HR increase from physiologic compensation to hypoxia, followed by rapid HR decrease prior to arrest.

Pots syndrome: the importance of organic screening in anxiety patients. Case report

Introduction16-year-old female who starts psychiatric follow-up due to episodes of anxiety crises with dizziness and tremors.Objectives To expose a case in which it is essential to rule out organic pathology in cases where there is anxiety and physical symptoms.MethodsCase report and literature reviewResultsThe patient explains that she was in a situation of conflict with her ex-partner, commenting that he did not accept the breakup. Sertraline was prescribed in ascending doses up to 100 mg per day with complete remission of anxiety. 8 months later, she went to the emergency room for loss of consciousness and tremor of the lower limbs. She was diagnosed with conversive disorder and was prescribed lorazepam up to 3 mg per day. Since then, there has been a worsening in the frequency of syncope occurring up to 10 times a day, limiting her academic and social life. She was evaluated by a cardiologist who diagnosed Pots Syndrome (postural orthostatic tachycardia syndrome) and started treatment with ivabradine and mineralocorticoids. With this treatment, the episodes were drastically reduced and spaced out to 1-2 per week. The dose of lorazepam is decreased until its withdrawal without worsening of the anxious symptomatology.ConclusionsThis disorder consists of an involvement of the autonomic nervous system in which there is a sudden drop in blood pressure together with an abrupt increase in heart rate. Its treatment is based on increasing blood volume with drugs such as corticosteroids as well as postural measures with adequate water intake.DisclosureNo significant relationships.

Comparison of effects of dexmedetomidine added to ropivacaine versus ropivacaine alone infiltration scalp block for attenuation of the haemodynamic response to skull pin placement in neurosurgical procedures: A double-blind, randomised clinical trial.

Background and Aims:Skull pin head holder application is intensely painful and is accompanied with abrupt increase in heart rate and arterial blood pressure. We aimed to determine the effects of adding dexmedetomidine to ropivacaine scalp block in attenuating the haemodynamic response to skull pin insertion in neurosurgical procedures.Methods:Sixty patients were randomly allocated to receive scalp block with 25 ml of 0.5% ropivacaine added with either normal saline (control group) or dexmedetomidine (1 μg/kg) after anesthesia induction. A standard uniform general endotracheal anaesthesia protocol was followed in all study subjects. Heart rate and blood pressure measurements were made at baseline, 1, 3, 5, 10, and 15 min following skull pin placement. Student's independent t-test, Chi-square test and repeated measure analysis of variance were used to analyse the obtained data.Results:There was no significant attenuation of heart rate (P = 0.418), systolic (P = 0.542), diastolic (P = 0.793) and mean blood pressure (P = 0.478) with addition of dexmedetomidine to ropivacaine.Conclusions:The addition of dexmedetomidine (1 μg/kg) to 25 ml of 0.5% ropivacaine offers no additional benefit over 25 ml of 0.5% ropivacaine alone scalp block in attenuating the haemodynamic response to skull pin placement in neurosurgical procedures.

Abstract 392: Incidence Of Paroxysmal Supraventricular Tachycardia In The United States

Background: Paroxysmal supraventricular tachycardia (PSVT) encompasses a range of heart rhythm disorders that lead to abrupt increases in heart rate. Given its episodic nature, PSVT can be difficult to capture in a clinical setting. Therefore, estimating incidence of PSVT is challenging and thus limited data is available on the incidence of this disease. Objective: Estimate the incidence of PSVT within the United States in contemporary practice. Methods: Using claims, enrollment, and demographic data from the IBM Marketscan® Commercial Research Database (&lt;65y) and the Medicare Limited Dataset (≥65y), individuals enrolled in health plans for at least 5 continuous years from 2008-2016 were identified. Patients having claims with a PSVT diagnosis (ICD-9: 427.0; ICD-10 I47.1) on 2+ outpatient visits, 1+ ED visit, or 1+ inpatient admission were included in the analysis. Only patients receiving an initial diagnosis of PSVT in year 5 of continuous enrollment were included in the incidence calculation in order to avoid including prevalent cases. Incidence was projected to the US population based on the 2018 US census data. Results: Among 18,057,297 patients, 86,614 met PSVT criteria. Incidence rates were higher in female and older patients. Within the 18-44y group, the incidence rate was 1.9-fold higher for females as compared to males. Overall incidence rate per 100,000 was 79.1 and 107.2 for males and females respectively (Table). Projected to the 2018 US Census, there were 305,548 incident PSVT cases in 2018. Conclusion: There were over 305,000 incident cases of PSVT in 2018 with higher rates in female and older patients. Further studies are needed to understand practice patterns in management of PSVT, given the high incidence of this disease.

Physiological parameter values in greyhounds before and after high-intensity exercise.

Dog sports competitions have greatly expanded. The availability of reference values for each type of activity could help assess fitness accurately. Heart rate (HR), blood lactate (BL) and rectal temperature (RT) are relevant physiological parameters to determine the dogs response to effort. Previous studies in greyhounds have reported the effect of high-intensity exercise on many physiological parameters immediately after completing different racing distances and recovery times. However, there are no studies concerning physiological changes over shorter racing distances. We therefore assessed the effect of sprint exercise on HR, BL and RT in nine greyhounds performing sprint exercise over a 100-m distance chasing a lure. After the exercise, dogs underwent a passive 10-min recovery phase. Before the exercise, immediately after it and at 5 and 10 min during recovery, HR and RT were assessed and blood samples were collected for BL determination. HR, BL and RT values increased significantly after the exercise (P<0.01). Whereas HR returned to pre-exercise values at 10 min during the recovery phase (P>0.1), BL concentration and RT remained increased (P<0.01). The abrupt increase in HR, BL and RT values observed immediately after the exercise indicates the high intensity of the effort performed. Similarly, BL concentration after the exercise exceeded the 4 mmol/L lactate threshold, suggesting a predominant anaerobic metabolism during effort. Although HR returned to pre-exercise values 10 min after the exercise, a more extensive recovery phase would be necessary for a total return to resting values, particularly for BL and RT. In greyhounds subjected to high-intensity exercise, HR, BL and RT were reliable physiological parameters to accurately assess the physiological response to effort. The use of sprint exercises over short racing distances could be useful for appropriately monitoring fitness in sporting dogs.

96-78: Title: Heart rate of supporters during FIFA world cups

Introduction: 102 fans of different national football teams participate in a simple, non-binding study devoted to football supporters during the last three FIFA world cups. We studied changes occurring in heart rate during football matches, taking into account both the cardiovascular risk factors of the participants, and the relative importance of the match as first round, last sixteen to semi finale, and finale. Methods: Data were prospectively collected in 102 patients between june 2006 and july 2014 during the last three FIFA world cup of football. Participants were 18 to 62 years old. Heart rate and cardiac events were recorded in the 10 minutes before and during the match using a five derivations Holter ECG monitoring device (Searlight GE and Spiderview Sorin Group). Cardiovascular risk factors, medications and score of passion were also recorded. Results: Average heart rate significantly increased during the matches ( mean change 30 beats per minutes, p= 0.02). The maximum heart rate reached 95% or more of the maximal heart rate for age in 80% of the participants. Supra ventricular ectopic beats and paroxymal atrial fibrillations were observed in 10 subjects (9.8%). In bivariate analysis, goals, faults, supported team's victory, relative importance of the event and higher scale of passion were positively associated with average heart rate during matches and with cardiac events (all p < 0.05) (all p <0.05). Conclusions: During football competitions in World cup, supporters experience abrupt increases in heart rate, which compare to changes expected in maximal treadmill exercise tests, what should be taken into account, especially for those with overt cardiac diseases, or high global cardiovascular risk. Maximal heart rate of supporters during the last three World Cups of football (percentage refers to maximal theoretical heart rate). Maximal heart rate of supporters during the last three World Cups of football (percentage refers to maximal theoretical heart rate).

Central command differentially affects aortic and carotid sinus baroreflexes at the onset of spontaneous motor activity

Our laboratory has recently demonstrated that central command provides selective inhibition of the cardiomotor component of aortic (AOR) baroreflex during exercise, preserving carotid sinus (CS) baroreflex. To further explore the differential effects of central command on the arterial baroreflexes, we surgically separated the AOR and CS baroreflex systems, to identify the input-output relationship of each baroreflex system using brief occlusion of the abdominal aorta in decerebrate cats. Baroreflex sensitivity for heart rate (HR) was estimated from the baroreflex ratio between the pressor and bradycardia responses during aortic occlusion and from the slope of the baroreflex curve between the changes in mean arterial blood pressure (ΔMAP) and ΔHR. Spontaneous motor activity accompanied the abrupt increases in HR and MAP. When aortic occlusion was given at the onset of spontaneous motor activity, the baroreflex ratio was blunted to 11-25% of the preexercise value in either intact or AOR baroreflex. The slope of the ΔMAP-ΔHR curve was similarly attenuated at the onset of spontaneous motor activity to 11-18% of the slope during the preexercise period. In contrast, in the CS baroreflex, the baroreflex ratio and curve slope were not significantly (P>0.05) altered by spontaneous motor activity. An upward shift of the baroreflex curve appeared at the onset of spontaneous motor activity, irrespective of the intact, AOR, and CS baroreflex conditions. Taken together, it is concluded that central command provides selective inhibition for the cardiomotor limb of the aortic baroreflex at the onset of exercise, which in turn contributes to an instantaneous increase in HR.

Anesthetic management of a patient with hypertrophic cardiomyopathy and patent ductus arteriosus

Anesthetic management of a patient with hypertrophic cardiomyopathy and patent ductus arteriosus

Abstract 18722: Cardiac Stimulation Occurs with Electronic Control Devices and is Dependent Upon Subject Size, Dart Location, and Device Characteristics

Introduction Electronic control devices (ECDs) are weapons used to incapacitate violent subjects. Subjects have died suddenly after ECD application but since cardiac arrhythmias have been inconsistently observed during ECD application to animals, the cause for death is uncertain. We hypothesized that cardiac stimulation, if apparent during ECD application, could be detected by transesophageal echocardiography (TEE) and, if present, could be related to the model of ECD. Methods Four Yorkshire pigs were anesthetized, paralyzed with vecuronium, and restrained in a supine position. A GE 6T echo probe was placed in the esophagus to directly visualize left ventricular function. M-mode echocardiography was used to estimate heart rate. Two dart locations, chest and abdomen, were assessed. ECD energy application was delivered from one of 5 commercially available devices (Taser X26, Singer S200 AT, Taser M 26, Taser X-3, and Taser C2, all with different waveform characteristics) in random order to each pig, 4 times in each orientation. Results Cardiac stimulation, characterized by an abrupt increase in heart rate, reduction in myocardial contractility and mitral valve standstill, was detected with chest dart application in small pigs with all devices except the Taser X3 and in large pigs only with the S200 AT device (Table 1). Cardiac stimulation did not occur with abdominal dart application. VF was not observed. Conclusion Cardiac stimulation occurs during ECD application in pigs. Stimulation is dependent upon dart orientation and pig size. Refinement in waveform characteristics may result in ECD’s with a lower risk of cardiac stimulation. Table 1: Heart Rate Response During ECD Stimulation *P &lt; 0.0001 comparing cardiac heart rate with abdominal heart rate (Group 1)

Abrupt increase in heart rate during the transition from non-REM sleep to wakefulness and its utility for estimating sleep stages

Abrupt increase in heart rate during the transition from non-REM sleep to wakefulness and its utility for estimating sleep stages

Time course of synergistic interaction between DOCA and salt on blood pressure: roles of vasopressin and hepatic osmoreceptors

In DOCA-salt rats, the time course of the synergistic interaction between osmolality and DOCA to produce hypertension is unknown. Therefore, in rats 2 wk after implantation of subcutaneous silicone pellets containing DOCA (65 mg) or no drug (sham), we determined blood pressure (BP) and heart rate (HR) responses, using telemetric pressure transducers, during 2 wk of excess salt ingestion (1% NaCl in drinking water). BP was unaltered in sham rats after increased salt, but in DOCA rats BP increased within 4 h. The initial hypertension of 30-35 mmHg stabilized within 2 days, followed approximately 5 days later by a further increment of approximately 30 mmHg. HR first decreased during the dark phase; the second phase was linked to an abrupt increase in HR and BP variability and decreased HR variability. Pressor responses to acute intravenous hypertonic saline infusion were doubled in DOCA-treated rats via vasopressin and nonvasopressin mechanisms. Only in DOCA-treated rats, portal vein hypertonic saline infusion increased BP, which was prevented by V(1) vasopressin blockade. After 2 wk of DOCA-salt, oral ingestion of water rapidly decreased BP. Intraportal infusion of water did not lower BP in DOCA-salt rats, suggesting that hepatic osmoreceptors were not involved. In summary, the hypertension of DOCA-treated rats consuming excess salt exhibits multiple phases and can be rapidly reversed. Hypertonicity-induced vasopressin and nonvasopressin pressor mechanisms that are augmented by DOCA, and hepatic osmoreceptors may contribute to the initial developmental phase. With time, combined DOCA-salt induces marked changes in the regulation of the autonomic nervous system, which may favor hypertension development.

Sleep processes exert a predominant influence on the 24-h profile of heart rate variability.

Adverse cardiovascular events are known to exhibit 24-h variations with a peak incidence in the morning hours and a nonuniform distribution during the night. The authors examined whether these 24-h variations could be related to circadian or sleep-related changes in heart rate (HR) and in HR variability (HRV). To differentiate the effect of circadian and sleep-related influences, independent of posture and of meal ingestion, seven normal subjects were studied over 24 h, once with nocturnal sleep from 2300 to 0700 h and once after a night of sleep deprivation followed by 8 h of daytime sleep from 0700 to 1500 h. The subjects were submitted to constant conditions (continuous enteral nutrition and bed rest). HRV was calculated every 5 min using two indexes: the standard deviation of normal R-R intervals (SDNN) and the ratio of low-frequency to low-frequency plus high-frequency power. Sleep processes exerted a predominant influence on the 24-h profiles of HR and HRV, with lowest HRV levels during slow wave sleep, high levels during REM sleep and intrasleep awakenings, and abrupt increases in HR at each transition from deeper sleep to lighter sleep or awakenings. The circadian influence was smaller, except for SDNN, which displayed a nocturnal increase of 140% whether the subjects slept or not. This study demonstrates that 24-h variations in HR and HRV are little influenced by the circadian clock andare mainly sleep-stage dependent. The results suggest an important role for exogenous factors in the morning increase in cardiovascular events. During sleep, the sudden rises in HR at each transition from deeper sleep to lighter sleep or awakenings might precipitate the adverse cardiac events.

Effects of Hot Bath Immersion on Autonomic Activity and Hemodynamics

Hot bathing has been associated with sudden death and so the present study investigated its effects on autonomic activity and hemodynamics in the elderly patient and the healthy young by analyzing heart rate variability (HRV). Subjects were 9 elderly men (mean age, 75 years) and 9 young men (mean age, 27 years), who were immersed up to shoulder level while in a sitting position for 10min with the bath temperature at 40 degrees C. Blood pressure (BP) and heart rate (HR) were monitored. BP in the young decreased during bathing (p<0.01), whereas in the elderly BP had a maximum value just at the start of immersion (p<0.05) with a slight decline at 4 min after the start of immersion. Although HR in the young increased (p<0.01), in the elderly there was an abrupt increase in HR just at the start of immersion (p<0.05), followed by a decrease in HR. With regard to HRV, the high-frequency (HF) component in the young men was suppressed during immersion (p<0.01), but was unaffected in the elderly. The LF (low frequency)/HF ratio in the elderly decreased at 4 min (p<0.05). In conclusion, hypotensive syncope may cause sudden death by drowning during hot bathing, and is a consequence of the decrease in sympathetic tone that develops approximately 4min after immersion.

Cardiovascular morbidity in obstructive sleep apnea

The repetitive respiratory events that characterize obstructive sleep apnea (OSA) are each followed by abrupt increases in heart rate and in pulmonary and systemic artery pressure and by sudden decreases in right and left ventricular stroke volume. The changes in systemic pressure may be profound, with patients who are normotensive while awake having systolic pressures approaching 300 mm Hg after apnea termination. Because of these dramatic hemodynamic oscillations during sleep, many clinicians and investigators have postulated a connection between sleep-disordered breathing and cardiovascular morbidity and even mortality. This review critically examines the evidence for such a causal relationship. We begin, however, by reviewing the normal hemodynamic changes that occur during sleep. We then describe the acute hemodynamic events associated with OSA. Finally, we summarize the evidence for and against a causal connection between sleep apnea and cardiovascular morbidity. Copyright © 1999 by W.B. Saunders CompanyProgress in Cardiovascular Diseases, Vol. 41, No. 5 (March/April), 1999: pp 367-376

Rate and time dependent effects of D-sotalol on the monophasic action potential after sudden increase of the heart rate.

Experimental and clinical data suggests that almost all Class III antiarrhythmic agents diminish their ability to prolong cardiac repolarization at fast heart rates. However, only limited data exists about the time course of efficacy decay of Class III agents after sudden increase of the heart rate. In the present study, we assessed both rate and time dependent changes of the efficacy of d-sotalol in higher stimulation frequencies following an abrupt increase in heart rate. This might imitate the situation seen in the development of paroxysmal tachycardias. Monophasic action potentials were recorded from the right ventricular apex during sinus rhythm and constant stimulation with the paced cycle length (PCL) of 550 ms, 400 ms, and 330 ms in the baseline and 20 minutes after intravenous administration of d-sotalol (2.5 mg/kg) in seven patients with documented life-threatening ventricular tachyarrhythmias. D-sotalol significantly prolonged monophasic action potential duration at different steady-state heart rates (sinus rhythm: 21.1% +/- 3.6%; PCL 550 ms: 16.6% +/- 4.3%, 400 ms: 11.2% +/- 2.7%, 330 ms: 5.8% +/- 2.1%). The prolongation is significantly shorter in higher steady-state pacing, confirming a pronounced reverse-use dependent decrease of the efficacy of d-sotalol at faster stimulation frequencies. After the abrupt increase in heart rate, the beat-to-beat adaptation of the postdrug action potential prolongation exhibits only slight reverse-use dependent shortening. The decrease of the efficacy of d-sotalol is insignificant for the first 20 consecutive beats at the stimulation frequency of the PCL of 400 msec (from 16.6% at PCL of 550 ms to 14.6% at the 20th beat of the PCL of 400 ms), and for the first ten consecutive beats at the stimulation frequency of the PCL of 330 ms (from 16.8% at PCL of 550 ms to 12.3% at the 10th beat of the PCL of 330 ms). This slow decay of action potential prolongation after an abrupt increase in heart rate might contribute to the antiarrhythmic action of d-sotalol in cardiac tachyarrhythmias.

Differences in arousal response between aged and middle-aged patients with obstructive sleep apnea syndrome.

The aim of this study is to show the clinical significance of the differences in arousal response at a termination of apnea/hypopnea between aged and middle-aged patients with obstructive sleep apnea syndrome (OSAS). We polygraphically assessed electrocardiographic (ECG) and electroencephalographic (EEG) arousal. Electrocardiographic arousal was defined as an abrupt increase in heart rate at a termination of apnea/hypopnea. Our findings showed that EEG and ECG arousal at a termination of apnea/hypopnea were significantly suppressed in aged patients with OSAS, which might provide useful information on the pathophysiology, of OSAS.

The Rise Time of the Monophasic Action Potential

The kinetics of global use-dependent conduction slowing produced by sodium channel blockers in the human heart, estimated as a change in the QRS width, are known to be similar to those of use-dependent block of the maximum rate of depolarization in in vitro studies. However, the kinetics of the regional use-dependent decrease in conductivity have not been investigated. We examined whether the rise time of the monophasic action potential would be clinically useful as a marker of the local use-dependent decrease in conductivity by sodium channel blockers. In 12 patients without organic heart disease, monophasic action potentials (MAPs) were recorded at the right ventricular endocardium using a contact electrode before and after the administration of disopyramide (n = 6, 2 mg/kg, i.v.) or pilsicainide (class Ic agents, n = 4, 1 mg/kg, i.v., and n = 2, 150 mg, po) while the stimulus frequency was abruptly increased from 100/min to 150/min. The rise time, defined as the interval from the pacing pulse to the first peak deflection of the monophasic action potential, and the ORS width were measured simultaneously. In the absence of the sodium channel blockers, the abrupt increase in heart rate did not alter the QRS width or the rise time. In the presence of the agents, both variables were lengthened exponentially. The rate constants of onset changes in the QRS width and the rise time were 2.1 +/- 0.5 beats and 2.1 +/- 0.4 beats after the administration of disopyramide, and 7.5 +/- 3.0 beats and 8.2 +/- 4.0 beats after pilsicainide, respectively. The rate constant of the rise time was closely correlated with that of the QRS width. The present results are very closely comparable with the onset rate constants of use-dependent block of the maximum rate of depolarization in in vitro studies. These results suggest that (1) the rise time is a good indicator of local use-dependent decrease in conductivity by sodium channel blockers in human hearts and (2) the local use-dependent decrease in conductivity has kinetics similar to those of use-dependent sodium channel blocks.

Effect of chronotropic response pattern on oxygen kinetics.

The sinus node is considered to be the model of chronotropic response for pacemakers that use artificial rate modulating sensors. Maximal metabolic exercise testing with measurement of oxygen consumption (VO2) is frequently used to evaluate chronotropic response. Since activities of daily living are generally transient and involve submaximal effort, maximal exercise testing may not provide the most clinically relevant method of assessing rate modulation. The purpose of this study was to determine if an abrupt increase in heart rate (HR) at the onset of submaximal exercise provides improved oxygen kinetics compared with a linear response. Thirteen patients with complete heart block and permanent rate modulating pacemakers implanted following catheter ablation of the atrioventricular junction for refractory atrial fibrillation were chosen for study. The patients first completed a maximal treadmill exercise test using the chronotropic assessment exercise protocol with breath-by-breath analysis of expired gases. The expected HR at 50% of metabolic reserve was calculated for each patient. Three submaximal constant workload exercise tests were then performed at 50% of each patient's metabolic reserve, with the pacemaker randomly programmed to provide three different patterns of chronotropic response: linear (in which HR increased from 70 beats/min to the expected HR at 50% of metabolic reserve), fast (in which HR was abruptly increased to the expected HR at 50% of metabolic reserve), and slow (VVI at 70 beats/min). Oxygen kinetics were compared for the three patterns of chronotropic response. Cumulative oxygen (O2) consumption was significantly greater for the fast pattern (3610 mL) as compared with the linear (3487 mL, P = 0.004) or slow pattern (3277 mL). The O2 deficit was lower for the fast (361 +/- 139 mL) than for the linear (539 +/- 225 mL, P = 0.003) or slow chronotropic pattern (559 +/- 194). Similar improvements in the rate constant of O2 uptake and Borg perceived exertion scores were observed with the fast chronotropic response pattern. A rapid increase in pacing rate at the onset of exercise improves oxygen kinetics and results in less perceived exertion as compared to a more gradual rate increase that is more characteristic of sinus node behavior.