Electrocardiographic Changes in Patients Undergoing Hemodialysis

ABSTRACT

INTRODUCTION: Patients with end-stage renal disease who are on long-term dialysis support have a very high mortality. Nearly half of deaths on dialysis are secondary to myocardial infarction, cardiac arrest, malignant arrhythmias, and other cardiac causes. The purpose of the present study was to compare electrocardiogram (ECG) disturbances before and after hemodialysis.

METHODS: The participants were 144 patients on dialysis who met specific inclusion criteria. Their mean (SD) age was 56.27 (14.2) years. A cross-sectional study was conducted between June and December, 2009. Twelve-lead ECGs were performed in identical conditions for all patients, 10 minutes before and 10 minutes after the midweek morning hemodialysis session. Duration and amplitude of P wave and QRS complex, and duration of QTc and QTd were calculated. ECGs were analyzed by a single observer who was blind to all patient information. The Kolmogorov Smirnov, Wilcoxon signed rank, and McNemar tests were used to compare the variables before and after hemodialysis.

RESULTS: The mean duration of the QRS complex and QTc were significantly higher after dialysis (P = .043 and P = .007, respectively). There were no significant differences in the mean P wave duration or mean QTd (P > .05). There was a significant increase in the mean P wave and QRS complex amplitudes after hemodialysis (P = .0001). There were no significant differences between the number of patients with normal and abnormal values before and after dialysis for the duration of QRS complex, P wave, QTc, or QTd, or the amplitude of the P wave and QRS.

CONCLUSION: In the present study, ECG changes before and after hemodialysis presented as a significant increase in duration and amplitude of QRS, amplitude of P wave, and duration of QTc. ECG changes, especially QT intervals, should be monitored in patients with a history of hemodialysis in order to decrease cardiac complications.

KEYWORDS: Electrocardiographic analysis; Hemodialysis.

CORRESPONDENCE: Gholamreza Mokhtari, MD, Urology Research Center, Guilan University of Medical Sciences, Razi Hospital, Sardare Jangal Street, Rasht, Guilan 41448, Iran ().

CITATION: Urotoday Int J. 2010 Jun;3(3). doi:10.3834/uij.1944-5784.2010.06.03

ABBREVIATIONS AND ACRONYMS: ECG, electrocardiography/electrocardiogram; QRS-c, QRS complex; QTc, QT interval corrected for heart rate; QTD, QT dispersion.

INTRODUCTION

Patients with end-stage renal disease on long-term hemodialysis support have a very high mortality rate [1,2]. The main cause of this mortality is cardiac disease, which accounts for approximately 43% of all deaths. The causes of cardiac death include myocardial infarction, cardiac arrest, malignant arrhythmias, and other cardiac disorders [3,4,5,6,7]. Over 60% of cardiac deaths in patients undergoing dialysis (25â€“27% of all causes of mortality) are due to sudden cardiac death [1].

Patients undergoing dialysis are known to have high incidences of coronary artery disease and cardiomyopathy, but disturbances in electrolyte metabolism might also contribute to arrhythmia or abnormal conduction. Electrocardiography (ECG) findings, particularly the QT interval, QT dispersion (QTD), and the QT interval corrected for heart rate according to Bazett's formula (QTc), can be considered direct indicators of risk for developing arrhythmia in patients on hemodialysis [8]. However, these measures are not yet proven reliable and have not been consistently used by physicians to monitor their patients.

QTD is a crude and approximate measure of general abnormality of repolarization. It is defined as the difference between the longest (QTmax) and shortest (QTmin) QT intervals for a given set of 12 complete ECG leads. It reflects regional differences in ventricular recovery time, and has been linked to the concurrence of malignant arrhythmia associated with different cardiac diseases. Patients on hemodialysis have a significantly higher QTD when compared with healthy individuals, and QTD rises significantly after hemodialysis is completed [9]. QTc is calculated as QTD corrected by heart rate using Bazettâ€™s formula QTc= QT/(RR)^Â½, where RR is the interval from the onset of one QRS complex to the onset of the next QRS complex, measured in seconds [10]. QTc has been proposed as a noninvasive electrocardiographic parameter that might predict an increased risk of malignant arrhythmias. The normal range for QTD is 40-50 ms, with a maximum of 65 ms. The risk for serious ventricular arrhythmias or sudden death was observed in persons with QTD > 65 ms. Most studies have shown that automatic measurement of QTD is highly reproducible, and therefore reliable [8,11]. However, there are few studies reporting this measure in patients with a history of hemodialysis, particularly in the authors' geographic region.

If patients at high risk for cardiac complications could be reliably identified, therapy targeted at managing their disorder may reduce the risk of death. The purpose of the present study was to compare ECG disturbance before and after hemodialysis.

METHODS

Participants.

The participants were 144 patients from the hemodialysis unit of Razi Hospital in Rasht, evaluated between June 2009 and December 2009. Inclusion criteria were: (1) stable health for > 3 months; (2) hemodialysis session of 5 hours; (3) diet of 1.2 g/kg/day protein, 50 mmol sodium, and restricted potassium and phosphate; (4) antihypertensive drugs used only if hypertension persisted after sustained and careful examination of the patientâ€™s dry weight and appropriate adjustment to fluid intake and dialysis practice; (5) negative history of chest pain; and (6) serum electrolytes (including sodium, potassium, calcium, and phosphate) within the normal range. Exclusion criteria were chosen to elucidate the role of hemodialysis treatment, so that the data were not confounded by preestablished cardiovascular morbidity. The exclusion criteria included patients with: (1) diabetes mellitus; (2) overt ischemic heart disease (IHD); (3) ECG evidence of left ventricular hypertrophy (LVH) or left bundle-branch block (LBBB); (4) atrial fibrillation; (5) echocardiographic LV ejection fraction of <60%; and 5 patients taking class I or III antiarrhythmic drugs.

Out of the 144 total N, 77 patients (53.5 %) were male and 67 patients (46.5%) were female. The mean age was 56.27 years (SD, 14.2; range, 17-85 years).

Procedures

The study was approved by the Medical Ethics Committee of Guilan University. All participating patients signed an informed consent. A cross-sectional research design was used.

The patients were placed in a supine position. Twelve-lead ECGs were performed in identical conditions for all patients, 10 minutes before and 10 minutes after the midweek morning hemodialysis session. All ECGs were recorded after a 5-minute rest period. Duration and amplitude of P wave and QRS complex were recorded. Normal range for amplitude and duration of P wave were defined as 2-3 mV and 6-12 ms, respectively. Normal range for amplitude and duration of QRS complex were defined as 5-30 mV and 6-10 ms, respectively. The sum of the T waves from all 12 ECG leads was calculated. The T wave duration was measured in all leads from the first electrical activity to the offset at the junction between the end of T wave deflection and the isoelectric line. The QRS duration was also measured in all leads from the beginning of the QRS complex to the offset at the junction between the end of S wave deflection and the isoelectric line. The amplitude of QRS complexes in all 12 ECG leads were measured from peak to nadir in millimeter (to the nearest 0.5 mm) by employing a magnifying glass and calipers; the QRS sum was calculated.

All ECGs were coded and the QT intervals were analyzed by a single observer. The observer was blind to patient information. The QT interval was measured from the onset of the QRS complex to the end of the T wave, defined by the return of the terminal T wave to the isoelectric TP baseline. Three successive QT interval measurements were performed for each of the 12 leads, and the mean value was calculated. The maximum QT interval (QTc-max) was corrected for heart rate using Bazettâ€™s formula QTc= QT/(RR)^Â½. The QT (QTc) dispersion was determined as the difference between the maximum and the minimum of the QT (QTc) in different leads (minimum of 10) on the same recording. A QTc interval > 440 ms was considered abnormally prolonged. The normal range for QT dispersion is 40â€“50 ms, with a maximum of 65 ms.

Statistical Analyses

Results of quantitative variables were reported as means and standard deviations. The Kolmogorov Smirnov test and Wilcoxon signed rank test were used to compare the nonparametric continuous data before and after hemodialysis. The McNemar test was used to compare noncontinuous variables before and after hemodialysis. Comparisons were considered significantly different at P < .05.

RESULTS

Table 1 contains the means, standard deviations (SD), z scores, and probability values for the ECG duration and amplitude measures before and after hemodialysis. The mean duration of the QRS complex was significantly higher after dialysis (P = .043). Similarly, the mean duration of QTc was significantly higher after dialysis (P = .007). An example of ECG recordings showing differences in QRS and QTc before and after dialysis are shown in Figure 1 and Figure 2, respectively. There were no significant differences in mean P wave duration or mean QTd after dialysis. There was a significant increase in the mean P wave and QRS complex amplitudes after dialysis (P = .0001).

The mean heart rate was 79.24 beats/min and 80.67 beats/min before and after hemodialysis, respectively. The mean heart rate was significantly higher after hemodialysis (P = .029).

Table 2 contains the number of patients with normal and abnormal ECG duration and amplitude measures before and after hemodialysis and the probability of significant differences. There were no significant differences between the number of patients with normal and abnormal values before and after dialysis for the duration of QRS complex, P wave, QTc, or QTd. Similarly, there were no significant differences between the number of patients with normal and abnormal values before and after dialysis for the amplitude of the P wave and QRS.

DISCUSSION

P wave duration and dispersion, defined as the difference between the maximum and minimum P duration, are regarded as very important noninvasive ECG markers for assessing risk of atrial arrhythmia [12]. Previous studies have shown that hemodialysis ends with a significant increase in P wave maximum duration and P wave dispersion, which might be responsible for the increased occurrence of atrial fibrillation in these patients [13]. After hemodialysis sessions, mean QTc interval and QTc dispersion significantly increased [14]. Corrected QT interval dispersion (QTdc) may be a useful marker for identifying dialysis patients at an increased risk for overall and cardiovascular mortality [15]. Hemodialysis leads to an augmentation in the amplitude of the QRS complexes (QRS-c) and R waves [16]. An increase in the amplitude of electrocardiogram QRS complexes (upward arrow QRS) with hemodialysis has been invariably documented [17].

In the present study, there were no significant differences in mean P wave duration and amplitude after hemodialysis. Additionally, there were no significant differences between the frequency of normal and abnormal P wave duration and amplitude. There are conflicting reports of the effect of dialysis on these measures in the literature. Ozmen et al [18] showed that Pmax and P wave dispersion did not change significantly after hemodialysis. The authors concluded that these 2 parameters can be used as an indicator of effective hemodialysis. SzabÃ³ et al [19] showed that the mean (SD) P maximum of 58 (16) ms at the beginning of dialysis significantly increased to 98 (8.9) ms at the end of dialysis (P < .0001). Predialysis P dispersion of 23 (10) ms significantly increased to 41 (16) ms by the end of the sessions (P < .0001). Ozben et al [20] recorded the results of electrocardiograms immediately before, at the end of the second hour, and at the end of the dialysis sessions. They also found that P wave dispersion significantly increased during hemodialysis sessions, with means of 41 (12) ms and 21 (10) ms before and at the end of dialysis, respectively (P < .001). The P wave dispersion then decreased to a value of 24 (7) ms after hemodialysis, which was not significantly different from the predialysis values. Tezcan et al [2] showed that there was a significant increase in Pmax between 98 (13) ms at the beginning of dialysis and 126 (12) ms at the end (P < .001). There were no significant changes in Pmin. P wave duration significantly increased from a beginning mean of 27 (9) ms to an ending mean of 52 (11) ms (P < .001). Ozcan et al [21] showed that predialysis and postdialysis mean P wave dispersions significantly increased in patients undergoing dialysis when compared with control participants, but the mean voltage of predialysis and postdialysis LP20 were significantly reduced (P < .05).

In the present study, there was a significant increase in the mean QRS complex duration after hemodialysis (P = .043), but there was no significant difference in the frequency of normal or abnormal QRS complex duration or amplitude. An increase in the amplitude of the QRS complex following hemodialysis has been amply documented in the literature [22]. Ojanen et al [23] showed a nearly fourfold increase in mean QRS-VD during the dialysis session (372 +/- 300%), changing from 4.16 (2. 40) μV to 15.60 (7.0) μV (P < .001). This change was due to a difference in amplitude, because the duration of the QRS complex was not significantly altered. Jaroszynski et al [24] showed that the total mean amplitude of the QRS complex before hemodialysis was 13.09 (3.3) mV, which increased significantly after hemodialysis to 17.68 (4.03) mV (P < .001). An increase of QRS amplitude was observed in 35 out of 48 patients (72.92%).

In the present study, there was a significant increase in the mean duration of QTc after hemodialysis (P = .007). However, there were no significant differences in the frequency of normal and abnormal QTc or QTd. Floccari et al [25] found that an increase in QTc dispersion occurred during the first hour of the dialysis session. Milone et al [26] found that QT and QTc dispersion were significantly higher in patients undergoing hemodialysis than in control participants (P < .01, P < .04, respectively). When compared with predialysis values, Drighil et al [27] found that mean QT significantly decreased from 380.9 (38.4) ms to 363.5 (36.8) ms (P = .001) after dialysis, mean QTc did not significantly change (406.2 [30.8] ms to 405.4 [32.2] ms), and mean QTd significantly increased from 31.3 (14.6) ms to 43.9 (18.6) ms (P = .003) after dialysis.

CONCLUSION

In the present study, there were significant ECG increases in duration and amplitude of QRS, amplitude of P wave, and duration of QTc after hemodialysis. The authors recommend monitoring ECG changes, especially QT intervals, in patients with a history of hemodialysis in order to decrease cardiac complications.

Conflict of Interest: none declared

REFERENCES

Saravanan P, Freeman G, Davidson NC. Risk assessment for sudden cardiac death in dialysis patients: How relevant are conventional cardiac risk factors? Int J Cardiol. 2009 Apr 1. [Epub ahead of print].

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