Correlation between QRS Duration, Pulmonary Insufficiency and Right Ventricle Performance in Totally Corrected Tetralogy of Fallot.

OBJECTIVE: Despite progresses in surgical correction of Tetralogy of Fallot, pulmonary insufficiency and progressive dysfunction of the right ventricle impress its long-term prognosis. In this study we examined the correlations between QRS duration, pulmonary insufficiency and right ventricular performance index.
METHODS: We enrolled 57 repaired Tetralogy of Fallot patients. QRS duration on electrocardiogram, pulmonary regurgitation index (regurgitation time to diastolic time ratio), and right ventricular myocardial performance index were measured.
FINDINGS: There was a strong inverse correlation between QRS duration and pulmonary regurgitation index. However, significant correlation did not exist between QRS duration and right ventricular myocardial performance index. QRS duration ≥160 ms predicted severe pulmonary regurgitation with 100% sensitivity and 87% specificity.
CONCLUSION: Increased QRS duration can predict severity of pulmonary regurgitation.

Introduction

Patients with Tetralogy of Fallot (TOF), the most common cyanotic congenital heart disease, can have a long survival if their anomaly has been totally corrected with good results[. Pulmonary regurgitation (PR) and progressive dysfunction of the right ventricle (RV) are the most important threatening factors in the long-term prognosis of these patients[. Correlation between fatal arrhythmias and increased QRS duration >180 ms has been reviewed[. Magnetic resonance imaging (MRI) is considered the best method of investigating PR severity and RV dysfunction in corrected TOF patients. However, studies showed correlation with echocardiographic findings which is cheaper and more available[.

In this study we assessed the correlation between QRS duration on electrocardiogram (ECG), PR and RV performance index (RVMPI) to examine whether severe PR and RV dysfunction can be detected by surface ECG.

Subjects and Methods

Children with corrected TOF who visited our outpatient clinic from March 2008 to August 2010 were enrolled in this study. Patients with more than mild tricuspid valve insufficiency, residual ventricular septal defect (VSD) with a size >4 mm, residual pulmonary stenosis (PS) with a gradient >35 mmHg, left ventricle ejection fraction (LVEF) <50%, and other types of TOF including pulmonary atresia/VSD and double outlet right ventricle/VSD/PS were excluded from the study.

A 13-lead ECG and complete echocardiography exam were performed in all patients. On ECG, QRS complex duration in lead II was measured from the start of Q wave to end of S wave. PR was evaluated by continuous Doppler echocardiography at parasternal short axis view: PR duration and total time of diastole were measured and their ratio (PR index, PRi) was calculated[. We used RV myocardial performance index (RVMPI) to assess RV performance. We measured the time of blood ejection from the pulmonary artery using continuous Doppler at parasternal short axis view (a) and tricuspid valve opening to closure time using tricuspid valve continuous Doppler (b) and calculated RV MPI by the formula "(a-b)/b"[.

Statistical analysis was performed using SPSS version 11.5 program. A bivariate correlation was performed using Pearson correlation coefficient between QRS duration and both PRi and RVMPI. Statistical significance was inferred at a value level of P<0.05.

Findings

Fifty seven patients were enrolled in the study (30 males and 27 females) with the mean age 7.1±5.3 years at the time of study and the mean interval after surgery 2.3±2.1 years. Pearson analysis showed a strong inverse correlation between QRS complex duration and PRi (r=-.536, P<0.001) (Fig. 1). Only 1 patient had a QRS complex duration greater than 180 ms.

Fig. 1

Correlation between qrsd, QRS duration; Prix, PRi (r=-.536, P<0.001).

There was no statistically significant correlation between QRS complex duration and RVMPI (r=0.242, P=0.084). Only 3 patients had PRi <0.5 indicative of severe PR. One of the 3 was a 7 year- old boy who had a corrective surgery at the age of 1.5 years. His QRS complex duration and RVMPI were 180 ms and 0.6, respectively. Because of progressive RV dysfunction, cardiomegaly and hepatomegaly, homograft was implaned in his RV outflow tract. The other 2 patients with severe PR (PRi < 0.5) were 7 and 9 year-old boys with corrective surgery at the ages of 1 and 4 years, respectively. Their QRS complex duration was 160 ms and RVMPI 0.62 and 0.47, respectively. There were 7 other patients in the cohort with QRS duration ≥160 ms but PRi >0.5. Therefore, a QRS duration ≥160 ms can predict severe PR with 100% sensitivity and 87% specificity.

Discussion

TOF is the most common cyanotic heart disease (3.5-9% of congenital heart diseases)[. PR is a common complication after TOF correction[. Severe PR gradually causes RV dysfunction which needs pulmonary valve replacement. Several studies showed that pulmonary valve replacement improves ventricular function and functional class, stabilizes QRS duration, and decreases the rate of ventricular and atrial arrhythmias[ while its mortality is about 2% with few complications[. Murphy et al reported that among patients with surgically repaired TOF (rTOF), the overall 32-year actuarial survival rate was 86 percent; however, it remains lower than that in the general population[. The risk of late sudden death is low[.

The presence and degree of PR influence exercise tolerance, the incidence of atrial and ventricular arrhythmias, and the risk of sudden cardiac death (SCD)[. Life-threatening ventricular arrhythmias remain the greatest concern for the adult with rTOF. Incidence may be as high as 6%, and until the past decade there were no consistent identifiable risk factors for distinguishing patients at risk[. Gatzoulis et al[ provided the first clues to potential causes for ventricular arrhythmias in rTOF. They reviewed the clinical data of 178 adult survivors with rTOF after a mean follow-up of 21.4 years. Nine patients were found to have sustained ventricular arrhythmias, and four patients had postoperative SCD. They found that QRS duration >180 ms predicted sustained ventricular arrhythmias and SCD with 100% sensitivity, and that QRS duration correlated with RV size. Over the next few years, data supported the idea that the SCD risk in rTOF is a time-related risk factor that accelerates 20 to 25 years after surgical repair.

According to Li et al[, the ratio of PR time to total diastolic time is correlated with PR fraction in MRI: a value <50% indicates severe PR[. We used this ratio to assess PR intensity. Although we had only one QRS duration >180 ms and 3 PRi <50%, we showed that PRi inversely correlates with QRS duration. Long QRS duration is a result of RV dilation, which itself can be a result of severe PR[.

We used RVMPI as a factor to assess RV systolic and diastolic functions (normal range <0.3)[. We did not find a significant correlation between QRS duration and RVMPI. This may be due to small number of patients for detecting a weak correlation, late occurrence of RV dysfunction in the presence of severe PR and long QRS duration, and imperfectness of pulsed-Doppler RVMPI to precisely reflect RV function. Yasuoka et al showed that tissue Doppler RVMPI measurement is superior to pulse Doppler method used in our study, to detect RV dysfunction in rTOF patient with PR[.

Conclusion

Increased QRS duration can predict severity of PR.