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Jae Ung Lee, M.D., Kyung Soo Kim, M.D., Jeong Hyun Kim, M.D., Heon Kil Lim, M.D., Bang Hun Lee, M.D., and also Chung Kyun Lee, M.D.

You are watching: Why does the pr interval decreased during exercise


Address reprint researches to : Jae Ung Lee, M.D., Division of Cardiology, Department of Internal Medicine, College of Medicine, Hanyang College, #17 Haengdang-Dong, Seongdong-Ku, Seoul, 133-792, Korea
This is an Open Access article spread under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted noncommercial use, distribution, and reproduction in any kind of medium, offered the original job-related is properly cited.

Objectives:

The PR interval on the electrocardiogram represents conduction time from the oncollection of atrial activation with His-Purkinje conduction device during a normal cardiac cycle. While its actions at rest and also in the time of exposure to assorted cardioactive drugs is well documented, tbelow exist few reports which describe PR interval variations throughout exercise in normal manage and patient groups.

In the current study, We examined the behavior of the PR intervals during assorted stperiods of exercise, and also at the same time we oboffered whether the transforms of PR interval during exercise can indicate that implanted cardiac pacemaker algorithms might be built to maximize hemodynamic benefits in patients requiring physiological cardiac pacemaker.


Methods:

A retrospective analysis of the exercise treadmill test was percreated on 148 healthy regulate group(148 males, expect, age of 42.7±11.7) and also 134 patient group(95 males & 39 females, mean era of 47.1±11.7) which had complained of non-particular chest symptoms yet were figured out as normal in the exercise treadmill test. During the test, we offered the typical Bruce protocol. The results were expressed as suppose ± conventional deviation, and also distinctions in the suppose worth of each conventional deviation, and distinctions in the mean value of each group were evaluated by the student’s t-test. A P value of less than 0.05 was concerned as substantial.


Results:

The regulate group showed 6.9msec reduction rate of the PR interval whenever before their heart rate raised by 10 beats per minute.

The entire patients team showed 5msec reduction price of the PR interval whenever their heart rate increased by 10 beats per minute.

The male patients team verified 5.2msec reduction price of the PR interval whenever their heart rate enhanced by 10 beats per minute.

The female patient group verified 4.3msec reduction price of the PR interval whenever before their heart price increased by 10 beats per minute.

Tbelow were significant differences of the PR interval transforms in between the whole or male patient team and the control group within the very same array of heart rates.


Conclusions:

This study reflects that PR interval changes matching to heart price increments were lipractically reduced. These changes of PR interval in the time of exercise imply that implanted cardiac pacemaker algorithms might be created to maximize hemodynamic benefits in patients requiring physiological cardiac pacemakers.


Keywords: PR interval, Cardiac Pacemaker, Exercise Treadmill Test

INTRODUCTION

Due to the technical advancements of cardiac pacemaker, the ultimate function of therapy utilizing this gadget lies in the optimization of cardiopulmonary function rather than the straightforward survival of the patient. In various other words, the feature of the heart must be made to fulfill the metabolic demands of physical activities past the maintenance of cardiac output at relaxing state.

The programmable dual chamber cardiac pacemaker can feeling and also pace both the atrium and ventricle by controlling the atrioventricular(AV) conduction delay time. The atrioventricular synchrony aims that the atrium deserve to play an assistant function for the cardiac output by contracting atrium and ventricle at correct intervals and also therefore, the cardiac output can be boosted if the synchrony has actually been adequately adjusted in comparichild with the addressed PR intervals also throughout exercise and at resting state1).

For a normal perboy, the velocity of AV conduction will enhance according to the heart rate increases2,3). The changes of AV conduction can be measured by rating the PR intervals on the electrocardiogram(ECG).

The PR interval on the ECG means the moment taken from the activation of the atrium to the His-Purkinje conduction device by the transmission of electrical stimulation. Hence, its alters according to exercise anxiety will certainly reflect the boost of the intranodal conduction velocity because of physiologic or autonomic nervous system stimulations.

The duty of the atrial contraction for cardiac output has actually been renowned. That is, the function of the atrium will be affected by various determinants such as age, autonomic nervous system activity, heart rate, physical activity, AV conduction delay time and contracting problem of atrium and also ventricle.

It has actually been reported that as soon as a DDD-form cardiac pacemaker is supplied, appropriate reduction of AV conduction delay, according to heart rates, would certainly be even more valuable for the advancement of cardiac output fairly than a solved create of AV nodal delay.

With the over background in mind, this study was aimed at reviewing the physiologic transforms or functions of the PR intervals, because of exercise tension by suggests of the exercise treadmill test for patients that saw the hospital bereason of non-particular cardiovascular symptoms, but who were diagnosed as normal, and the civilian pilots that visited for their continual physical check-up.


MATERIALS AND METHODS

The topics of this research were those 134 patients(95 males and 39 females, mea period of 47.1±11.7) who visited to complain chiefly of non-particular chest pain, however who were diagnosed as normal on the exercise treadmill test, and 148 civilian pilots(all males, mea period of 42.7±11.7) Who saw for their continuous physical examination.

The patients and manage groups were all made to do the exact same exercise treadmill test using 12-lead ECG. The test was conducted according to the typical Bruce protocol and also the 12-lead ECG was checked at the rate of 50 mm/sec. The interval from the first deflection of p wave to QRS complicated in lead II was measured utilizing the caliper, and its outcomes were suggested via the unit of msec(Fig. 1). In order to repel any type of differential errors among examiners, the PR intervals were checked by the very same examiner. Cases of positive test for myocardial ischemia and less than 5 metabolic equivalents(METs) exercise capacity patients, were excluded from the research.



DISCUSSION

As the conduction delay time can be changed by the heart price in DDD-type cardiac pacing, as a result of the current technical development of the pacemaker mechanism, the co-connection in between cardiac output and also AV conduction delay time is being actively studied. Up to now, in order to determine the many correct AV conduction delay time, according to heart rate in the application of the man-made cardiac pacemaker, researches have actually been performed utilizing such suggests as systolic time interval4,5), echocardiogram6), Doppler echocardiogram7,8), radionuclide ventriculogram9) and also hemodynamic study10,11).

The programmable dual chamber cardiac pacemaker have the right to feeling and also pace both the atrium and also ventricle by controlling the AV conduction delay time in many ways. The artioventricular synchrony aims that the atrium can play an assistant duty for the cardiac output by contracting atrium and ventricle at correct intervals and therefore, the cardiac output have the right to be enhanced if the synchrony has been adequately readjusted in comparikid via the addressed PR intervals also during exercise and at resting state1,12,13). For a normal perboy, the velocity of AV conduction will be increased according to the heart rate increases2,3). The alters of AV conduction can be measured by rating the PR intervals on the ECG.

The PR interval on the ECG implies the time taken from the activation of the atrium to the His-Purkinje conduction mechanism by the transmission of electric stimulation. Thus, its alters according to exercise anxiety will certainly reflect the increase of the intranodal conduction velocity because of physiologic or autonomic nervous device stimulations.

It has actually been recognized from the researches so far that heart price, AV conduction delay time and also exercise tension are lialmost co-related1,14–16). In 1990, Barbieri et al.17) reported that heart rate and also AV conduction delay times are reversely co-connected in direct terms within the variety of 55–155 beats per minute of heart rate, yet PR interval seldom transforms past this variety.

But in our study the straight co-connection could be observed even within the array of 155–195 beats per minute of heart rate. In 1973, Tail et al.4) reported in their study utilizing ECG, carotid arterial phonogram and apex phonogram that the PR interval would certainly reach its height of stroke volume at 180–200 msec within the range of 70±20 beats per minute of heart price.

In 1975, Karlof et al.1) reported that the rate-matched VVI cardiac pacing would increase the cardiac output by 18% even more at relaxing state and 8% more throughout exercise than the atrial synchronous ventricular(VAT) pacing. These distinctions may be attributed to the atrioventricular synchrony, although they are not substantially, wide enough. In 1979, Greenberg et al.18) reported that the atrial contraction would not affect the stroke volume as soon as the left ventricular filling press is increased

In order to recognize the the majority of desirable cardiac pacing in physiologic terms, the heart rate need to be appropriately enhanced first according to the exercise stress and anxiety and also secondly, the velocity of AV conduction delay time need to be adequately diminished, for which the left ventricular feature is normal. What is crucial right here is to select the algorithms which deserve to determine the adjust of PR interval according to the heart price in applying the cardiac pacemaker. In 1985, Leguy and Kratz19), reported that 100 msec of AV conduction delay time would lead to a boost of more end-diastolic and stroke volumes, within the range of 92–115 beats per minutes of heart price, in comparison through 150 msec of AV conduction delay time within the same heart rate by using the bicycle ergometer test. In this study, it was disclosed that these patient groups differ much from those of normal control group(150–134 msec of PR intervals at 92–115 beats per minute of heart rate). In 1989, Mehta et al.20) reported in their research by making use of the Doppler echocardiogram, that 100–200 msec of AV conduction delay time at resting state and also 75–80 msec during exercise would boost the cardiac output.

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In 1990, Margaret et al.21) shelp in their research for 32 healthy and balanced males, that the AV conduction delay time have to be lessened to 3.5 msec per 10 beats, which differs a lot from the reduction price of 6.9 msec per 10 beats for the healthy and balanced male team in our research. This distinction may attributable to the racial element or the size of the subjects. This study has actually found the desirable equation y=−0.69×+213 at the price of 60–190 beats per minute of heart rate for the normal regulate team, which differs from the equation y=−0.50×+208 for the entire patient team. For the male patient group the equation is y=−0.52×+209, while it is y=−0.43×+207 for the female patient group. As can be seen, tbelow are little bit differences in between both sexes, however tright here deserve to be found some significant distinctions in between normal and male patient team at even more than 100 beats per minutes of heart rate. Although we performed the exercise treadmill test for the whole patient group who complained about nonparticular cardiovascular symptoms, they were all diagnosed as normal. Considering the suppose sensitivity of 68% and specificity of 77% of this exercise treadmill test, the possibility of their cardiovascular condition could not be excluded22). Upon reviewing the previous literature, there has been no study about the PR interval separating males from females. In this research there was no substantial distinction between both sexes of the patient team.