QT interval estimation in patients with right bundle branch block using validated formulas for left bundle branch block

Funding Acknowledgements

Type of funding sources: None.

BACKGROUND

Adequate measurement of the QT interval is of paramount importance in order to identify patients at higher risk for ventricular arrhythmias. Previous studies have described different methods to estimate baseline QT in patients with left bundle branch block (LBBB). However, the evidence regarding the assessment of QT interval in the setting of right bundle branch block (RBBB) is scarce. 

PURPOSE

We aimed to analyze the feasibility and accuracy of the different formulas described for LBBB in the estimation of the QT interval in RBBB. 

METHODS

We enrolled patients who underwent left sided electrophysiologic procedures. All patients were in sinus rhythm and had narrow QRS. Pacing was performed from the left atrial appendage for baseline measurements, and from the left aspect of the interventricular septum (selective capture of the left bundle was attempted) to measure RBBB QT and QRS. Pacing cycle length was 800 ms or slightly below patients´ intrinsic rhythm at both locations. Measurements were performed manually (using digital calipers) according to current recommendations and corrected using Bazett. Validated formulas for LBBB QT considered are described in table 1. 

RESULTS

50 patients (42 cryoballoon pulmonary veins isolation (PVI), 4 radiofrequency PVI, 4 concealed left accessory pathways). 70% were male. Mean age was 62 ± 11 years old. Left ventricle ejection fraction was 58 ± 10%. 66% and 60% of the patients were taking betablockers and antiarrhythmic drugs, respectively. Mean pacing cycle length was 707 ± 99 ms. Baseline measurements: QRS 95 ± 10, QT 391 ± 36, QTc 467 ± 39 ms. RBBB measurements: QRS 165 ± 21, QT 448 ± 46, QTc 531 ± 52 ms. Correlations between baseline and estimated QTc were good for all the formulas (table 1). Reliability analysis showed that both Yankelson and Wang methods had the highest intraclass correlation coefficients (ICC) when trying to estimate baseline QTc. 

CONCLUSIONS

Previously described formulas for LBBB exhibit marked differences regarding reliability in the estimation of QTc interval in the setting of RBBB. According to our results, Yankelson’s method shows the most consistent agreement when estimating baseline QTc interval in patients with RBBB. Table 1.LBBB METHODFormula to estimate baseline QTcPearson’s R correlation coefficientCI (95%)Intraclass correlation coefficientCI (95%)YankelsonQTc - QRS + 95 (m) or 88 (f)0.805(0.632-0.977)0.882(0.788-0.934)Bogossian**QT - (QRS/2)0.813(0.644-0.982)0.756(-0.127-0.919)Wang**QT - (0.86*QRS - 71)0.801(0.627-0.974)0.834(0.465-0.930)Tang-Rabkin0.945*QTcRabkin - 260.722(0.521-0.923)0.711(0.019-0.885)RautaharjuQT - 155*(60/heart rate - 1) - 0.93*(QRS - 139) - 22 (m) or - 34 (f)0.780(0.599-0.961)0.105(-0.017-0.381)**Bogossian and Wang required additional HR correction (Bazett).  Abstract Figure 1. Bland-Altman

P1820New parameters for the evaluation of mechanic and elastic properties of the aortic root in Marfan Syndrome

Background

Elastic properties of the thoracic aorta in patients with Marfan Syndrome (MS) have already been evaluated with classic echocardiographic parameters. In the latest years the use of Speckle-Tracking (STE) ecocardiography has been widely extended. Our aim is to describe and provide new parameters of aortic deformation measured by STE in patients with MS.

Methods

95 unoperated adult patients with MS and 32 healthy controls were prospectively enrolled. We measured classic parameters of the aortic root using 2D echocardiography. We calculated the posterior aortic wall systolic excursion at the sinuses of Valsalva and ascending aorta using M Mode in TDI colour; with ST 2D ecocardiography we measured the aortic strain at the sinuses of Valsalva (SV) and the anterior and posterior aortic wall displacement at the SV. Aortic distensibility was calculated using the formula: 1000 * (Ds − Dd)/Dd * 1/(Ps − Pd) in mmHg–1 (Ds: systolic and Dd: diastolic diameters, Ps systolic and Pd diastolic blood pressure). Aortic stiffness index was calculated as Ln((Ps/Pd)/(Ds-Dd)/Dd)).

Results

As shown in the table bellow, patients with MS had lower aortic strain, aortic anterior and posterior wall displacement and impaired aortic distensibility and stiffness index compared to healthy controls. We found a strong negative linear correlation between aortic root diameter at the SV and aortic root strain (r=−0.56, figure 1).

Results of statistical analysis MS (n=95) Controls (n=32) p Age (years) 32.84±12.35 32.41±7.98 0.85 Aortic root diameter at the sinuses of Valsalva (mm) 38.82±5.35 30.92±3.65 <0.001 Aortic root strain (%) 4.66±2.45 9.19±2.49 <0.001 Anterior aortic wall displacement STE (mm) 10.39±3.64 13.10±2.26 <0.001 Posterior aortic wall displacement STE (mm) 9.02±2.87 11.04±1.82 <0.001 Aortic distensibility 0.98±0.46 1.37±0.72 0.01 Aortic stiffness index 3.74±0.43 3.47±0.51 0.01 MS = Marfan Syndrome; STE = Speckle Tracking Ecocardiography.

Figure 1. Dispersion plot

Conclusions

Our results suggest that aortic deformation and displacement obtained by STE echocardiography is impaired in MS, showing a reduced distensibility and an increased stiffness of the aortic wall, with a strong negative correlation between aortic root dilation and aortic strain. All these parameters may be useful as additional tools for the diagnosis and follow-up of Marfan patients, and could be useful to to improve the echocardiographic evaluation of the aortic root.

P4374Biventricular systolic function analysis in patients with Marfan Syndrome using speckle-tracking 2D ecocardiography

Background

Left Ventricular systolic disfunction has already been described in Marfan Syndrome (MS) in patients without valvular dysfunction using 2D and 3D speckle tracking echocardiography (STE). This dysfunction has been related to a more severe causal genetic mutation, which suggest the presence of a primary cardiomiopathy in these patients. Right ventricular function has been less studied so far. We sought to evaluate biventricular function in our cohort of MS patients with 2D-STE.

Methods

95 unoperated adult patients with MS and 32 healthy controls were prospectively enrolled. Patients with more than mild mitral or aortic regurgitation were excluded. Using STE we obtanied left ventricular global longitudinal strain (LVGLS) from the average of 16 segments from 4,2 and 3-chamber views and RVGLS values were obtained from the average of 6 segments from the apical 4-chamber view. We also measured classic parameters of systolic biventricular function (LVEF and TAPSE).

Results

Compared to controls, patients with MFS had significantly lower LVGLS and RVGLS (table 1). Values obtanied for LVGLS in MS patients were at the lower limit of normality stablished in the latest cuantification guidelines, while RVGLS and RV free wall LS were slightly above the limit of normality. LVEF and TAPSE were also slightly diminished in MS patients, though the differences found were clinically not relevant.

Results of statistical analysis MS (n=93) Controls (n=32) p Age (years) 32.84±12.4 32.41±7.98 0.85 Aortic Root Diameter Valsalva Sinuses (mm) 38.82±5.35 30.91±5.3 <0.001 LVGLS (%) −18.93±2.62 −21.52±2.26 <0.001 RVGLS (%) −21.25±3.54 −24.68±3.08 <0.001 RV free wall LS (%) −22.09±3.92 −25.56±3.63 <0.001 LVEF (%) 59.5±5.34 63.27±4.19 0.001 TAPSE (mm) 23.97±4.57 25.82±3.32 0.03 MS = Marfan Syndrome; LVGLS = Left ventricular global longitudinal strain; RVGLS = right ventricular global longitudinal strain.

Conclusions

Our study suggests that patients with MFS show lower biventricular strain compared with healthy controls. 2D-STE imaging may be useful to detect subclinical changes in cardiac function in patients with MFS and should be added to routine ecocardiographic evaluation in order to improve the follow-up and treatment of these patients.