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Assessment of Ventricular
Synchronization by Fourier Analysis
in a Radionuclide Angiography

Peix, Amalia; Ponce, Felizardo; López, Adlin;
Zayas, Roberto; Cabrera, Omar;
Maltas, Ana María; Carrillo, Regla

Instituto de Cardiología y Cirugía Cardiovascular, La Habana, Cuba

SUMMARY
Introduction: Radionuclide angiography (RNA) permits the evaluation of segmental and global ventricular contractility, as well as the detection of conduction troubles.
Objectives: With the aim of assessing the temporal parameters of normal ventricular synchronization in the normal heart, we performed a third harmonic (3H) Fourier phase analysis in a RNA.
Material and Methods: Fifteen normal subjects (10 men and 5 women) were included. An equilibrium RNA was performed in 35-degrees left anterior oblique projection. The onset (T0), mean time (T1), total contraction time (Tt) for right (RV) and left ventricle (LV), as well as the interventricular time (TRV-LV) were measured on the 3H Fourier histograms of the time-activity curve.
Results: Right ventricle's contraction started 11ms before left ventricle (T0RV = 54±33 ms; T0LV = 65±13 ms), with a longer total contraction time (TtRV = 83±38 ms vs. TtLV = 61±19 ms). The interventricular time (TRV-LV) was 20±18 ms.
Discussion: The simultaneous contraction of both ventricles can be temporally quantified by RNA Fourier phase analysis with high reproducibility. The earliest epicardial breakthrough occurs at the anterior right epicardial surface near the apex, followed by the anterior and posterior paraseptal areas of the left ventricle and the activation of the rest of both ventricles. Among our cases, RV started its contraction before the LV. We can only assess the mechanical pattern of activation and not the electrical propagation of the cardiac impulse.
Conclusion: The simultaneous contraction of right and left ventricles can be quantified by RNA phase analysis, providing a useful tool for ventricular resynchronisation assessment in multisite pacing.

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INTRODUCTION
   In general, the study of cardiac conduction pathways is done through invasive approaches, such as electrophysiology. But some noninvasive techniques: the radionuclide angiography (RNA) and the cardiac nuclear magnetic resonance provide some indirect information on this regard using contractility parameters. Radionuclide angiography has been used to evaluate patients with coronary heart disease and conduction abnormalities, as well as the origin of ectopic beats and ventricular tachycardias or the location of atrioventricular fibbers in pre-excitation syndromes.

   Phase analysis in a RNA provides a parametric map of sequential contraction, functional image that makes possible the interventricular synchronization assessment. This method has been proved with good results by Toussaint et al (Int J of Cardiac Imaging, in press).

OBJECTIVE
   To assess the temporal parameters of normal ventricular synchronization in the normal heart through a third harmonic (3H) Fourier phase analysis in a RNA.

MATERIAL AND METHODS
Study population
   Fifteen subjects (10 men and 5 women; mean age: 47±13 years), without prior cardiac diseases and with normal physical examination, electrocardiogram, chest X-rays and echocardiogram, were included.

Radionuclide angiography
   After in vivo labelling of red blood cells with 17 MBq of technetium-99m (99mTc) per kg of body weight, imaging was performed with a digital gamma camera (GCA 501S, Toshiba) in the 35-degrees left anterior oblique projection with a 10-degrees cranial tilt. Sixteen 64 x 64 frames corresponding to an average cardiac cycle were acquired until 3x106 counts were accumulated. Cycles with periods outside ± 10% of the average were rejected. Images were filtered for space-time high-frequency noise. A left ventricular region of interest (ROI) was constructed in end-diastolic and in end-systolic images. Background was determined from a periventricular ROI in the end-diastolic image. The left ventricular ejection fraction (LVEF) and the right ventricular ejection fraction (RVEF) were determined as follows:
EF = (Diastolic Activity-Systolic Activity) / (Diastolic Activity-Background Activity)

   Phase analysis was performed with a software that does a 3H Fourier assessment. A colour-coded image of the end-systolic phase angle is obtained as a map of sequential contraction. Two ROI were drawn for the left (LV) and right (RV) ventricles. A phase histogram was obtained for each ROI, measuring the onset (T0), mean time (Tm, determined by curve fitting of the histogram and representing the largest number of synchronous pixels), and total contraction time (Tt) for RV and LV. We calculated the final value of contraction time (Tf = Tt + T0) for each ventricle; the interventricular time (TRV-LV); the propagation time (TP = Tm - T0) for each ventricle, and the total propagation time (TTP = LV final time - RV onset time).

Statistical analysis
   All measurements were expressed as mean ± standard deviation, and expressed temporally in milliseconds (ms). The continuous variables were compared using a Wilcoxon-Mann-Whitney test. A probability value of p<0.05 was considered significant.

RESULTS
   Left ventricular ejection fraction was 65±5% and right ventricular ejection fraction was 48±12%. Temporal parameters of contraction are presented in Table 1.

   Right ventricle's contraction started 54 ms after the beginning of the QRS complex, and 11 ms before left ventricle, with a longer contraction time, but the differences were not statistically significant. The contraction ended in the right ventricle 22 ms after the left ventricle (p=NS).

   The LV and RV propagation time were 30±13 ms and 48±21 ms, respectively (p=0.01). The mean times for LV and RV were 96±13 ms and 102±16 ms, with an interventricular time TRV-LV = 20±18 ms. The total propagation time was 72±48 ms.

DISCUSSION
   The simultaneous contraction of both ventricles can be temporally quantified by RNA Fourier phase analysis with high reproducibility. The earliest epicardial breakthrough occurs at the anterior right epicardial surface near the apex, followed by the anterior and posterior paraseptal areas of the left ventricle and the activation of the rest of both ventricles. Among our cases, RV started its contraction before the LV.

   Our mean LV and RV propagation times (30 ms for the LV and 48 ms for the RV) were consistent with the electrophysiological measurements of the HV interval (30-55 ms), but lower than the values obtained by Toussaint et al (56 ms for the LV and 67 ms for the RV).

    The total time for transmission of the cardiac impulse from the penetrating portion of A-V bundle to the last of the ventricular muscle fibbers in the normal heart is about 100 ms, which corresponds well with our final value of contraction time in the left ventricle (126 ms). We also agree with the fact that RV ends its contraction several milliseconds before LV.

    Cardiac impulse excites the first ventricular muscle fibber only 60 ms ahead of the excitation of the last one, which agrees with our total propagation time of 72±48 ms. This explains how the different portions of the ventricular muscle in both ventricles start their contraction at almost the same time. Adequate pumping by the two ventricular chambers needs this synchronous contraction.

    Finally, it is important to point out that with this method we can only assess the mechanical pattern of activation and not the electrical propagation of the cardiac impulse itself. However, the results on the mechanical synchrony are very close to what would be expected from the electrical propagation pattern.

CONCLUSION
   The simultaneous contraction of right and left ventricles can be quantified by RNA phase analysis, providing a useful tool for ventricular resynchronisation assessment in multisite pacing.

 

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2nd Virtual Congress of Cardiology

Dr. Florencio Garófalo
Steering Committee
President
Dr. Raúl Bretal
Scientific Committee
President
Dr. Armando Pacher
Technical Committee - CETIFAC
President
fgaro@fac.org.ar
fgaro@satlink.com
rbretal@fac.org.ar
rbretal@netverk.com.ar
apacher@fac.org.ar
apacher@satlink.com

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