vectorcardiographic features in patients receiving transcatheter closure of atrial septal defect

W. Carson, J. K. Wang¹, Y. Z. Tseng
Cardiovascular Division, Department of Internal Medicine,
and
¹Paediatric Cardiology, Department of Paediatrics, National Taiwan University Hospital
No.7, Chung-Shan South Road, Taipei , Taiwan 100

Abstract: Eighteen patients enrolled a study of the transcatheter closure of atrial septal defects by the Amplatzer occluder. Frank lead vectorcardiograms were recorded pre- and post-operation. The participants were three males and 15 females ( 16.8 + 16.4 years ). Fourteen (77%) patients changed the sense of inscription direction of the P loop, which may indicate a pathological condition in transforming a process back to nearly normal status, except the occluder in situ is not human tissue. Fourteen (77%) patients had changes of the notch of the P loop. This is highly suggestive of electrophysiological “hibernating” myocardium in these paediatric patients. The magnitude of the maximal spatial P, QRS vectors did not obviously change after the procedure. Eight (44%) patients changed the sense of the inscription of the QRS loop. Among the eight, six had changes in the Left Sagittal plane. This may indicate reducing different degrees of the right ventricular enlargement after transcatheter closure of the atrial septal defects.

INTRODUCTION

The first successful transcatheter closure of a secundum atrial septal defect was reported in 1976 [1], but the requirement for a very large (23F) delivery catheter precluded its application to paediatric patients. There was no vectorcardiographic report of 3-dimentional electrical activity changes of the heart’s reaction to the procedure in the literature. This unprecedented research is intended to document vectorcardiographic features in patients with the transcatheter closure of the secundum type of atrial septal defects. The FDA approved   Amplatzer occluder on the 6^th December 2001.

METHODS

Eighteen patients enrolled a study of the transcatheter closure of atrial septal defects by the Amplatzer occluder (AGA Medical Corp., Golden Valley, Minn.). Thirteen were paediatric patients and the remaining five were adults. They received electrocardiographic and vectorcardiographic examinations before and after the procedure. A Fukuda Denshi Vectorcardiograph model VA-3GA was used for the Frank lead X, Y, Z, orthogonal electrocardiogram and vectorcardiogram. In addition to the complete recording of the P-QRS-T loop complex in the three planes (Horizontal (H), Left Sagittal (LS), and Frontal (F) ) , highly magnified spot tracings of the P loop were taken for detailed analysis.

RESULTS

There were three male and 15 female patients. Their ages ranged between three and 60 years; mean +  SD was 16.8+ 16.4 years.

Changes of the Maximal Spatial P vector (mV)

Compared with pre-closure tracings the maximal spatial P vector had 12 decreased, but six increased magnitude after closure of the atrial septal defects. The pre- vs post- Amplatzer occluder maximal spatial P vector was 0.0796+ 0.019 mV vs 0.0764 + 0.019 mV. 

Changes of the sense of inscription direction of the P loop

Fourteen (77%) of the 18 patients changed the sense of inscription direction of the P loop after the Amplatzer deployment. These changes were initially from clockwise, anti-clockwise, or figure-of-eight patterns into a different pattern in the same plane. Ten patients changed in only one plane of the post-operative vectorcardiogram. In addition, four patients changed in two planes of the  vectorcardiogram. Four of the ten patients changed in only one plane turning into the normal sense of inscription direction of the P loop after catheter occlusion of the atrial septal defect. However, four patients changed in two planes, only one plane turning into the normal sense of inscription direction of the P loop after the procedure.

Changes of  the  notch of the P loop

After comparing the pre- and post-procedure vectorcardiogram, 14 (77%) of 18 patients had changes of the notch of the P loop. There were only six patients in  one plane, four in two planes, and four in the three planes in the vectorcardiogram.

Changes of the sense of inscription direction of the QRS loop

Eight (44%) of 18 patients changed the sense of inscription of the QRS loop in the post-occlusion vectorcardiogram. Six had changes in one plane, one had changes in two planes, and the remaining one had changes in the three planes. Among the eight, six had changes in the LS plane. Four patients of the eight changed the sense of inscription direction of the QRS loop back to normal, and one patient changed three planes with the LS plane remaining abnormal.

Changes of the Maximal Spatial QRS vector (mV)             

The maximal spatial QRS loop had six increased, and 12 decreased magnitude after the transcatheter closure of the atrial septal defect. The pre- vs post- Amplatzer occluder maximal spatial QRS vector was 0.35 + 0.14 mV vs 0.33 + 0.20 mV.

DISCUSSION

There was no obvious difference in the maximal spatial P vector between pre- and post-transcatheter closure of the atrial septal defect. This may indicate that a successful closure of the atrial septal defect might not change gross electromotive power immediately, at least for the time being.

Changes of the sense of inscription direction of the P loop indicate electrical propagation within the atria. This may indicate a pathological condition returned to nearly normal status except the occluder in situ is not human tissue. Interestingly, changes of  the  notch of the P loop are also documented in this report. The notch to the P loop is similar  to the bites of the QRS loop. This study had a majority of paediatric patients. Therefore, the notch is highly suggestive of electrophysiological “hibernating” myocardium in our paediatric patients. Indeed, this may explain the myth of why bites of the QRS loop sometimes fail to show a correlation between myocardial lesions demonstrated by pathological [2], angiographic and coronary arteriographic examinations [3] in the literature. Therefore, there may be subgroups within the bites phenomenon.

The maximal spatial QRS vector did not have obvious changes in magnitude before and after the procedure. This may suggest that the ventricles are far away from the atria. Further evidence supporting this is the change of sense of inscription direction of the QRS loop. In other words, propagation of the depolarization process in the ventricles is less frequently changed than the depolarization process of the atria after an operation. It should be noted that the most frequently changed plane in the vectorcardiogram is the LS plane. Because most LS planes changed   back to normal inscription direction in the vectorcardiogram, this might indicate reducing different degrees of the right ventricular enlargement. Indeed, the sense of inscription direction of the QRS loop in the LS plane can be either clockwise or figure-of-eight in patients with an ostium secundum type of atrial septal defect; anterior convexity of the afferent limb of the QRS loop in the LS plane indicates right ventricular enlargement in this kind of patients [4].  

Readers should be aware that the sense of the inscription direction of the P, QRS loops, notches of the P loop, and the LS plane in the vectorcardiogram are not readily available from the scalar ECG. Whether or not all of our patients will eventually return to normal vectorcardiogram after transcatheter closures of the secundum type of atrial septal defect, will need long-term follow-up study. The study is in progress at the moment 

REFERENCES

[1]  T.D. King, N.L. Mill. “Secundum atrial septal defects: nonoperative closure during cardiac catheterization” JAMA, vol. 235, pp. 2506-9, 1976.

[2]  R.H. Selvester, H.B. Rubin, J.A. Hamlin, et al.. “New quantitative vectorcardiographic criteria for the detection of myocardial infarction in diabetes”. Am Heart J, vol. 75, pp. 335-348,  1968.

[3]  R.J. Maron, R.H. Selvester, E.J. Ellis. “Selective cine coronary arteriography and vectorcardiographic diagnosis: A correlative study of one hundred patients”. Am Heart J, vol. 82, pp. 163-170,  1971

[4] S. Toyama, K. Suzuki, T. Ishiyama, et al. “Vectorcardiographic criteria of left and right ventricular hypertrophy with the Frank system” Jpn Circ J, vol 30, pp. 189-194, 1966.