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ORIGINAL ARTICLE
Year : 2021  |  Volume : 10  |  Issue : 2  |  Page : 37-39

The effect of basic cycle length stimuli on effective refractory period measurement


Department of Cardiac Electrophysiology, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran

Date of Submission11-Jan-2021
Date of Decision02-Mar-2021
Date of Acceptance25-Mar-2021
Date of Web Publication29-Jul-2021

Correspondence Address:
Dr. Mohammd Ali Sadr-Ameli
Department of Cardiac Electrophysiology, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rcm.rcm_1_21

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  Abstract 


Background: Refractory periods are measured by the extrastimulus technique, whereby a single extrastimulus is introduced at progressively shorter coupling intervals until a response is no longer elicited. Purpose: As refractoriness of cardiac tissues depends on prior cycle length, refractory periods should be determined at a fixed cycle length within the physiologic range. The extrastimulus is delivered after a train of 8 to 10 paced complexes to allow time for reasonable stabilization of refractoriness, which is usually accomplished after the first 3 or 4 paced beats. Objectives: We conducted this study to compare the effect of 6 vs 8 stimuli in basic cycle length (BCL) in measurement of effective refractory period (ERP). Materials and Methods: During electrophysiologic study (EPS) of 100 consecutive patients, anterograde and retrograde ERP of atrioventricular node (AVN) were measured by introduction of 6 vs 8 stimuli in BCL and premature beat, then the results were compared. Results: Recorded anterograde and retrograde ERP of AVN applying 6 vs 8 stimuli in BCL were compared and no difference was detected. Conclusion: We concluded that for ERP measurement of AVN, 6 stimuli in BCL is comparable to 8 stimuli in reaching the steady state.

Keywords: Basic cycle length. effective refractory period, stimuli number


How to cite this article:
Sadr-Ameli MA, Kamali F, Vahedinezhad M, Sadrameli S. The effect of basic cycle length stimuli on effective refractory period measurement. Res Cardiovasc Med 2021;10:37-9

How to cite this URL:
Sadr-Ameli MA, Kamali F, Vahedinezhad M, Sadrameli S. The effect of basic cycle length stimuli on effective refractory period measurement. Res Cardiovasc Med [serial online] 2021 [cited 2021 Oct 21];10:37-9. Available from: https://www.rcvmonline.com/text.asp?2021/10/2/37/322578




  Introduction Top


The cardiac cell is absolutely refractory from the beginning of the action potential (AP) upstroke till the return of it to threshold potential. In nearly the first half of relative refractory period, the cell cannot respond to even increased stimulus strength (and if a response is elicited, it cannot propagate). Hence, effectively, this period is also absolutely refractory. Addition of this period to absolute refractory period (ARP) makes effective refractory period (ERP) [Figure 1].
Figure 1: Schematic representation of ERP. RMP: Resting membrane potential, Th.P: Threshold potential, ARP: Absolute refractory period, RRF: Relative refractory period

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The refractoriness of a cardiac tissue can be defined by the response of that tissue to the introduction of premature stimuli. In clinical electrophysiology, refractoriness is generally expressed in terms of three measurements: relative, effective, and functional. The definitions differ slightly from comparable terms used in cellular electrophysiology.

The ERP of a cardiac tissue is the longest coupling interval between the basic drive and the premature impulse that fails to propagate through that tissue.

The ERP of a tissue or structure is the longest coupling interval that fails to capture the tissue or be conducted over the structure. Near its ERP, a structure may propagate an impulse, but with some delay. Thus, the coupling interval of the output impulse is longer than that of the input impulse.

In human, refractory periods are measured by the extrastimulus technique, whereby a single atrial or ventricular extrastimulus is introduced at progressively shorter coupling intervals until a response is no longer elicited.[1],[2] Because refractoriness of cardiac tissues depends on prior cycle length (CL), refractory periods should be determined at a fixed CL within the physiologic range (1000–600 ms) to avoid the changes in refractoriness that would occur owing to alterations in CL secondary to sinus arrhythmia or spontaneous premature complexes. The extrastimulus is delivered after a train of 8–10 paced complexes to allow time for reasonable stabilization of refractoriness, which is usually accomplished after the first 3 or 4 paced beats.[3],[4]

Although the basic drive CL affects the refractory periods in this predicted way, abrupt changes in the CL may alter refractoriness differently. The effect of abrupt changes in drive CL and/or the effect of premature impulses on subsequent refractoriness of His-Purkinje and ventricular tissue have been studied.[1],[2],[3],[5],[6],[7]


  Methods Top


In the current study, 100 patients with the diagnosis of atrioventricular nodal (AVN) reentrant tachycardia and atrioventricular reentrant tachycardia were recruited consecutively from the outpatient arrhythmia clinic of Rajaie Heart Center in 2019. All patients underwent electrophysiologic study (EPS), and slow pathway or accessory pathway ablation was done. During EPS, anterograde and retrograde ERP (AERP and RERP) of the AVN were calculated for each patient after 6 and then 8 pacing stimuli in basic drive. Fifty-five patients were male and the average age of our patients were 38 ± 7 (18–55) years. None of the patients took antiarrhythmic drugs.

Statistical analysis

To perform the statistical analysis, we used SPSS version 18.0 (SPSS, Inc., USA). Normality of variables' distribution was evaluated using the Kolmogorov–Smirnov test. Between-group comparisons were made by paired sample t-test, and scatter plots were used to demonstrate the inclines of the fit lines. A P < 0.05 was considered statistically significant.


  Results Top


In this study, 100 patients who needed EPS were included. AERP and RERP of the AVN were calculated in each patient after applying 8 and then 6 pacing stimuli in BCL [Figure 2].
Figure 2: AERP of AVN after 8 (upper tracing) and 6 stimuli (lower tracing) in basic drive. ERP in both situations were 280 ms. AERP: Anterograde effective refractory period, ERP: Effective refractory period, AVN: Atrioventricular node

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Recorded AERP and RERP of the AVN in these patients were compared using paired sample t-test, and no difference was detected [Table 1].
Table 1: Paired differences, means, confidence interval, and P

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We also used scatter plots to demonstrate paired values of 8 and 6 pacing beats [Figure 1] and [Figure 2]. As shown, the inclines of both AERP and RERP fit lines are very near to 1 (0.98 and 0.97 respectively) [Figure 3] and [Figure 4].
Figure 3: Paired scatter plot to show differences between AERP 6 and 8 values. AERP: Anterograde effective refractory period

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Figure 4: Paired scatter plot to show differences between RERP 6 and 8 values. RERP: Retrograde effective refractory period

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In case of arrhythmia induction during ERP measurement, the arrhythmia was interrupted and ERP measurement was reevaluated.


  Discussion Top


The concept of applying 8–10 stimuli in BCL or basic drive has been suggested by Josephson years ago.[8] He proposed that steady state in conduction system could be reached after as few as 3–4 stimuli.

If we can apply 6 stimuli in BCL, we may save the time in the long run. Hence, we compared 6 versus 8 stimuli and noticed that ERP is nearly the same. In other words, the steady state could be reached even by 6 stimuli.

To the best of our knowledge, there is no report in this field.

Stimulus strength has definitely effective in the ERP measurement. We know that the measured ERP of atrial and/or ventricular sites of stimulation is inversely related to the current used, that is, the measured ERP will decrease when higher stimulus strengths are used. In most electrophysiologic laboratories, stimulus strength has been arbitrarily standardized as being delivered at twice diastolic threshold.[6]

Shortening of the ERP primarily occurs at short coupling intervals beginning from 50 to 100 ms above the ERP determined during the basic drive CL. This effect on refractoriness was linearly related to the drive CL such that premature stimuli at comparable coupling intervals delivered at 400 ms would produce a shorter ERP than those associated with 600 ms.

Determinations of refractoriness should be performed at multiple drive CLs to assess the effect of CL on the refractory periods. There are expected physiologic responses to alterations in drive CLs. Normally, atrial, His-Purkinje, and ventricular refractory periods are directly related to the basic drive CL, that is, the ERP tends to decrease with decreasing drive CLs.[9]

Shenasa et al.[10] studied the differential effects of abrupt CL changes on the refractoriness of AP, his purkinje system (HPS), and atrial and ventricular myocardium. They did not look at the number of basic drive stimuli but short to long and vice versa in CL.

Ethical clearance

Ethics Clearance is obtained for the this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Damato AN, Lau SH, Patton RD, Steiner C, Berkowitz WD. A study of atrioventricular conduction in man using premature atrial stimulation and His bundle recordings. Circulation 1969;40:61-9.  Back to cited text no. 1
    
2.
Wit AL, Weiss MB, Berkowitz WD, Rosen KM, Steiner C, Damato AN. Patterns of atrioventricular conduction in the human heart. Circ Res 1970;27:345-59.  Back to cited text no. 2
    
3.
Cagin NA, Kunstadt D, Wolfish P, Levitt B. The influence of heart rate on the refractory period of the atrium and A-V conducting system. Am Heart J 1973;85:358.  Back to cited text no. 3
    
4.
Denes P, Wu D, Dhingra R, Pietras RJ, Rosen KM. The effects of cycle length on cardiac refractory periods in man. Circulation 1974;49:32-41.  Back to cited text no. 4
    
5.
Akhtar M, Damato AN, Batsford WP, Ruskin JN, Ogunkelu JB. A comparative analysis of antegrade and retrograde conduction patterns in man. Circulation 1975;52:766-78.  Back to cited text no. 5
    
6.
Greenspan AM, Camardo JS, Horowitz LN, Spielman SR, Josephson ME. Human ventricular refractoriness: Effects of increasing current. Am J Cardiol 1981;47:244-50.  Back to cited text no. 6
    
7.
Akhtar M, Denker ST, Lehmann MH, Mahmud R. Effects of sudden cycle length alteration on refractoriness of human His-Purkinje system and ventricular myocardium. In: Zipes DP, Jalife J, editors. Cardiac Electrophysiology and Arrhythmias. Orlando, FL: Grune & Stratton; 1985. p. 399.  Back to cited text no. 7
    
8.
Josephson ME. Electrophysiologic investigation. In: Clinical Cardiac Electrophysiology, Techniques and Interpretations. 3rd ed. Lippincott Williams & Wilkins, Philadelphia: Lippincott Williams & Wilkins; 2002. p. 19-67.  Back to cited text no. 8
    
9.
Damato AN, Lau SH. Clinical value of the electrogram of the conduction system. Prog Cardiovasc Dis 1970;13:119-40.  Back to cited text no. 9
    
10.
Shenasa M, Lacombe P, Cardinal R, Page P, Sadr-Ameli MA. Differential effects of abrupt cycle length changes on the refractoriness of accessory pathway, His-Purkinje system, atrial and ventricular myocardium in Wolff-Parkinson-White syndrome. Pacing Clin Electrophysiol 1989;12:29-40.  Back to cited text no. 10
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1]



 

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