Academic Editor: Matteo Bertini
The electrophysiological activity of the heart is recorded and presented in form
of electrocardiogram (ECG). In 1998 the concept of P wave dispersion as the risk
factor for atrial fibrillation (AF) recurrence was introduced. It was calculated
as the difference between the longest and the shortest P wave. The aim of our
study is to prove that the P wave dispersion is an artifact of low accuracy in P
wave measurement. The study included 186 patients (78M 108F) aged 59.7
The electrical activity of the working myocardium is measurable and can be graphically represented by a 12-lead electrocardiogram. In this form of recording, the electrical signal is recorded by 10 electrodes, which form 6 limb leads: 3 bipolar, 3 unipolar and 6 unipolar precordial [1, 2]. Each limb lead records the flow of electric current in the frontal plane and the precordial leads in the horizontal plane. The polarity of either bipolar or unipolar pair of electrodes allows the myocardial depolarization (which is essentially a change in potential from negative to positive), to produce the appropriate deflection [3, 4]. The deflection is positive if the momentary current-vector is lined up with the direction of the bipolar lead or is oriented towards the unipolar lead, or is set negatively in the opposite situation. When the current flows perpendicular in relation to the direction of the bipolar lead, or parallel considering the direction of the unipolar lead, the leads do not register any deflection. This happens because there is no chrono-spatial change in the current flow regarding a particular lead [5, 6]. This fact results in the formation of isoelectric fragments of the electrocardiogram. Considering the complexity of the heart muscle structures, this is never the case in practice, however those facts let us understand some detailed phenomena in precise P wave interpretation. For example, the initial and the closing fragments of the electrocardiogram waveforms may appear to be isoelectric, but with the proper amplification the deflection of the line will be visible.
The described phenomenon is consistent with the general properties of current-flow recording: if a given phenomenon has started and is being recorded by some leads, one cannot assume that the phenomenon is not present in the other leads just because the amplitude of the recorded signal is low. For obvious reasons, the described problem more often concerns the electrical activity of the atrium, as the amplitude of the P wave is many times lower and more subtle than the QRS complex, due to the differences in the masses of the atria and ventricles. The described problem was the basis of the incorrect theory of the so-called ‘P wave dispersion’, introduced in the late 20th century [7]. Despite the critical work on the accuracy of the P wave measurement, which was also raised by the authors of the dispersion concept themselves [8, 9, 10], this theory has become established in medicine, leading to the creation of many works that describe this phenomenon based on insufficient accuracy of taking measurements [11, 12, 13, 14].
The use of the vector graphics and the electrophysiological system for the measurement of the P wave allowed for a much more accurate assessment [15, 16, 17]. In the following study, we want to show that, the problem of inaccuracy in the assessment of P wave duration is a common problem, and is only slightly dependent on the type of patient population with various atrial arrhythmias.
The aim of the study was to assess the duration of the P wave and its indices in a wide, unselected population of patients with common arrhythmias – atrioventricular nodal reentrant tachycardia (AVNRT), typical atrial flutter (AFL) and atrial fibrillation (AF), and to demonstrate the similarities in the inaccuracy of the P wave duration measurement depending on the method used.
The study included 186 patients (78M 108F) aged 59.7
P wave duration measured inaccurate and accurate and the visual
changes in presented electrocardiograms. (A) The measurements taken at the paper
speed of 25 mm/s, enhancement 8
The clinical baseline characteristics of the studied patients and the results of measurements of the P wave duration are presented in Table 1.
Variable | Group | p-value | ||||||
AVNRT, N = 62 | AFL, N = 62 | AF, N = 62 | ||||||
n | % | n | % | n | % | |||
Sex | 0.167 | |||||||
Women | 42 | 67.7% | 34 | 54.8% | 32 | 51.6% | ||
Men | 20 | 32.3% | 28 | 45.2% | 30 | 48.4% | ||
Comorbidities | ||||||||
HT | 37 | 59.7% | 44 | 70.1% | 46 | 74.2% | ||
DM | 5 | 8.1% | 11 | 17.7% | 13 | 21.0% | ||
CKD | 4 | 6.5% | 6 | 9.7% | 5 | 8.1% | ||
IHD | 6 | 9.7% | 12 | 19.4% | 11 | 17.7% | ||
HF | 4 | 6.5% | 7 | 11.3% | 6 | 9.7% | ||
Age, years | ||||||||
Mean |
54.2 |
60.4 |
64.5 |
|||||
Me [Q1; Q3] | 58 [45; 64] | 63 [53; 70] | 66 [58; 70] | |||||
Min to Max | 21 to 80 | 23 to 90 | 39 to 87 | |||||
DM, diabetes mellitus; CKD, chronic kidney disease; IHD, ischemic heart disease; HF, heart failure, HT, hypertension; AVNRT, atrioventricular re-entry nodal tachycardia; AFL, atrial flutter; AF, atrial fibrillation; SD, standard deviation; Me [Q1; Q3]: median I quartile range. |
Table 2 presents a summary of the measurement data concerning the duration and
dispersion of the P wave. Below we present the result of the Wilcoxon signed-rank
test for pairs of observations regarding the dispersion of the P wave measured by
the accurate (AM) and inaccurate (IM) methods. The difference between the P wave
dispersion determined from the measurement results by the imprecise and accurate
method is highly significant (46.6 ms vs. 4.6 ms; p
Statistics | Inaccurate method | Accurate method | p-value | |
P |
||||
Mean |
126.4 |
143.5 |
||
Me [Q1; Q3] | 122 [100; 145] | 141 [126; 162] | ||
Min to Max | 37 to 180 | 84 to 208 | ||
P |
||||
Mean |
77.4 |
138.9 |
||
Me [Q1; Q3] | 76 [56; 100] | 135 [121; 158] | ||
Min to Max | 23 to 138 | 84 to 201 | ||
P |
||||
Mean |
46.6 |
4.6 |
||
Me [Q1; Q3] | 44 [35; 59] | 4 [3; 7] | ||
Min to Max | 14 to 124 | –4 to 11 | ||
SD |
||||
Mean |
6.9 |
5.5 |
||
Me [Q1; Q3] | 6 [3; 9] | 4 [2; 7] | ||
Min to Max | 0 to 35 | 0 to 34 | ||
V |
||||
Mean |
6.1 |
15.1 |
||
Me [Q1; Q3] | 4 [2; 8] | 15 [13; 17] | ||
Min to Max | 0 to 37 | 10 to 25 | ||
SD |
||||
Mean |
9.5 |
5.6 |
||
Me [Q1; Q3] | 7 [4; 14] | 4 [2; 7] | ||
Min to Max | 0 to 49 | 0 to 37 | ||
V |
||||
Mean |
14.2 |
4.1 |
||
Me [Q1; Q3] | 9 [5; 17] | 3 [1; 3] | ||
Min to Max | 0 to 81 | 0 to 28 | ||
Ms, milliseconds; SD, standard deviation; V, variance; Me [Q1; Q3], median I quartile range. |
P wave duration dispersion measured inaccurate and accurate and the result of the signed rank test.
The coefficients of variation (CV% = SD / Mean
Comparison of the variability coefficients of the maximum and minimum P wave durations measured with inaccurate and accurate method and the result of the signed rank test.
Comparison of the coefficients of variability of the results of measurements made with inaccurate and accurate method of the maximum and minimum durations of the P wave and the results of the signed rank test.
The correlation between the P wave dispersion and the maximum and minimum time of the P wave duration are presented in Table 3.
Method | Parameter | All, N = 186 | AVNRT, N = 62 | AFL, N = 62 | AF, N = 62 |
Inaccurate | P |
0.292 | 0.167 | 0.390 | 0.266 |
P |
–0.319 | –0.519 | –0.117 | –0.461 | |
Accurate | P |
0.133 | 0.126 | 0.095 | –0.052 |
P |
0.018 | –0.041 | –0.026 | –0.159 | |
Correlation coefficients other than zero at the level of p |
The differences between imprecise and precise methodology of the P wave duration measurements are presented in Table 4.
Group: AVNRT | Inaccurate method | Accurate method | p-value | ||
N = 62 | N = 62 | ||||
P |
|||||
Mean |
107.2 |
126.6 |
|||
Me [Q1; Q3] | 109 [96; 120] | 125 [113; 134] | |||
Min to Max | 37 to 168 | 84 to 179 | |||
P |
|||||
Mean |
62.9 |
122.6 |
|||
Me [Q1; Q3] | 59 [47; 74] | 119 [111; 131] | |||
Min to Max | 23 to 117 | 84 to 176 | |||
P |
|||||
Mean |
44.4 |
4.0 |
|||
Me [Q1; Q3] | 44 [34; 56] | 4 [1; 7] | |||
Min to Max | 14 to 73 | –2 to 10 | |||
Group: AFL | N = 62 | N = 62 | |||
P |
|||||
Mean |
130.9 |
150.8 |
|||
Me [Q1; Q3] | 135 [109; 153] | 153 [133; 170] | |||
Min to Max | 62 to 179 | 98 to 195 | |||
P |
|||||
Mean |
87.6 |
146.4 |
|||
Me [Q1; Q3] | 92 [67; 111] | 149 [129; 164] | |||
Min to Max | 34 to 138 | 94 to 184 | |||
P |
|||||
Mean |
43.3 |
4.4 |
|||
Me [Q1; Q3] | 40 [33; 53] | 4 [3; 6] | |||
Min to Max | 14 to 70 | –4 to 11 | |||
Group: AF | N = 62 | N = 62 | |||
P |
|||||
Mean |
133.9 |
153.0 |
|||
Me [Q1; Q3] | 134 [122; 149] | 154 [134; 169] | |||
Min to Max | 80 to 180 | 109 to 208 | |||
P |
|||||
Mean |
81.7 |
147.6 |
|||
Me [Q1; Q3] | 82 [60; 103] | 152 [128; 164] | |||
Min to Max | 29 to 137 | 102 to 201 | |||
P |
|||||
Mean |
43.3 |
4.4 |
|||
Me [Q1; Q3] | 40 [33; 53] | 4 [3; 6] | |||
Min to Max | 14 to 70 | –4 to 11 | |||
SD, standard deviation; Me [Q1; Q3], median I quartile range; AVNRT, atrioventricular re-entry nodal tachycardia; AFL, atrial flutter; AF, atrial fibrillation. |
The differences between the P wave durations in men and women, using inaccurate and accurate methods are presented in Table 5.
Group | P (ms) | Women, N = 108 | Men, N = 78 | p-value |
Inaccurate | P |
46.5 (35.2–59.3) | 42.4 (34.3–56.0) | 0.515 |
P |
112 (100–143) | 129 (108–146) | 0.213 | |
P |
70 (54–100) | 80 (60–103) | 0.143 | |
Accurate | P |
4.3 (2.5–6.0) | 5.1 (3.0–7.0) | 0.109 |
P |
134 (121–162) | 145 (130–162) | 0.122 | |
P |
130 (116–158) | 141 (126–158) | 0.174 | |
P, P wave duration; ms, milliseconds; N, number of patients. |
There was no statistically significant relationship between the results of the P
wave duration measurement (ms) and the sex of the patients (p
Based on the above analysis, we can draw conclusions that the variability in the
measurement of the maximum and minimum P wave durations is much greater with the
imprecise (50 mm/s 8
The most important and the most spectacular achievement of our research is the
proof, that the duration of the P wave dispersion is clearly dependent on the
technology used to calculate it. Taking a closer look at the details of the
following topic, it’s reasonable to begin with basic electrocardiographic rule.
All electrocardiographic events are registered in all ECG leads in the same time
[18]. This is logical, because the leads should be perceived as the different
perspectives, from which the very same impulse is being observed. Objectively it
is impossible that the very same impulse begins or ends in different moments in
different leads. Therefore. it is simply against the basic physical rules
describing the relations of space and time. Despite this fact, in 1998 Dilaveris
et al. [7] introduced the P wave dispersion which was defined as the
difference between the longest and the shortest P waves in two different leads.
The authors calculated the P wave duration, with the use of ruler, magnifying
glass and the ECG millimeter-paper print, at the speed of 50 mm/s and 1 mV/cm
gain. The study group included 60 patients with paroxysmal AF, and the control
group included 40 healthy patients with the similar profile. The maximal P wave
duration of 110 ms and the dispersion of 40 ms were the differential factors
between the study and control group with the positive prediction of 89%. In the
study group the dispersion was 49+/– ms and in the control one – 28+/– ms,
which was statistically relevant. As a result, the definition of P wave
dispersion gained popularity in scientific world, and the methodology of research
has been repeated by many followers ever since. For example, Dogan et
al. [19], acquired the P wave dispersion of 53.2
The precursor of the new methodology was the team of Zimmer et al. [22]
who presented their results at the Europace conference in 2015. The authors took
the measurements for the first time at the settings: 50 mm/s, 8
The described results were confirmed by Puerta et al. [23], who noticed
and focused on the gaps in Dilaveris’es theory of heterogeneous, non-homogeneous
signal spread, which was the initial explanation of the P wave dispersion
phenomenon. Puerta enrolled 153 randomized patients for electrophysiological
procedures in his study. In order to verify the methodology described by Zimmer
et al. [22], the authors measured the P wave duration twice: first at:
20 mm/mV; 50 mm/s, 8
Discussing the precision of the P wave measurement, it is worth focusing on
details. For example, the thickness of the isoelectric line itself in the printed
ECG averagely equals one third of a millimeter (excluding the R peak in QRS
complex), and this thickness may correspond to about 6–7 ms. The isoelectric
line marks the beginning and end of the P wave, so the measurement of the segment
between the beginning and end with a ruler creates the possibility of falsifying
the result by about 14 ms. Another problem is the determination of the objective
beginning and end of the P wave. Usually, there is no specific cut-off point at
which one should start the measurement. The rise of the isoelectric line, is
smooth and often accompanied by line tremors, so-called artifacts. They appear
due to the electrical resistance at the boundaries of the electrode-gel-skin
mediums, and/or due to the minimal recorded electrical activity of human muscles
[24, 25]. In order to avoid the above-mentioned measurement inaccuracies, we
decided to use an electrophysiological system to have an insight into every
millisecond of recorded pulse. It should be added that, by using the vector
graphic, the electrophysiologic software allowed for the zoom of the ECG without
any quality loss of the record. Using the electrophysiological system, the
researchers were able to analyze the record at the rate of 1 px/1 ms using a 4K
TV as the screen. It should be remembered that even the slightest hand tremor can
disturb the measurement by a few milliseconds, with such settings [26]. The scale
of error with less precise methodology is incomparable. For comparison—Dilaveris et al. [7] used a magnifying glass in their research, which
means that all inaccuracies, artifacts and averages of the ECG recording at the
parameters of 50 mm/s, 8
Despite the accuracy, the most precise manual measurements of the P wave duration still seem to be an insufficient proof against the P wave dispersion theory. The main arguments against precise manual methodology are the subjectivity of measurement, and imperfection of a human eye while assessing the duration. In order to oppose these arguments, our team decided to develop an automatic, specially calibrated algorithm which analyses every millisecond of the recording as objectively as it is possible. We drew our inspiration from the algorithm used by Yamada in his research in 1999, who revealed spectacular results two years after the concept of the P wave dispersion had been introduced. Our algorithm called APPA (“Automatic Precise P wave Assessment”) was designed with help of an experienced professional software developer, who was priorly unfamiliar with the P wave measurements issues. The technology is directly based on the automatic analysis of vector graphics, simultaneously comparing and contrasting data from all 12 ECG leads. The automatic assessement is bound to maintain the repeatability of obtaining the results which will make the results more reliable. With this approach, the suggestion of subjectivity will be no longer adequate. We are under the process of testing the software and are planning to publish our first results by the end of October 2021.
The issues of P wave morphology and duration remains a living topic for research. Technological development allows for accurate measurements, but the theory of P wave dispersion is still deeply rooted in the scientific environment. The determination of total atrial activation time and the assessment of the P wave profile seem to be a promising direction of research in the future. Advanced analysis of these variables is bound to increase the chance of determining a new parameter for predicting recurrent atrial fibrillation in clinical practice.
(1) P wave dispersion reach negligible values tending to zero, after increasing the precision of measurement.
(2) Structural destruction of the atria results in “self-hiding” of the actual duration of the P wave in ECG. In clinical practice, this may contribute to an incorrect assessment of the degree of atrial destruction.
JZ and JG designed the research study. JZ, GZ, P-SW performed the research. JR provided help and access to all data in Cath lab systems. AS and JG analyzed the data. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript.
All data collected in the study were based on anonymous ECG recordings saved in electrophysiology system in the process of carrying out different procedures in Cath labs. The subjects gave their informed consent for anonymized data analysis for the scientific purpose. The study was conducted in accordance with the Declaration of Helsinki, and approved by the local Ethics Committee (approval number: KB 813/2019).
We are deeply grateful to all peer reviewers who helped our team in the process of writing of this manuscript.
This research received no external funding.
The authors declare no conflict of interest.