Computed-Tomography a Powerful Tool for Diagnosis of Pediatric and Adult Congenital Heart Disease: Methodology and Interpretation Guide

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© 2015 Jami G. Shakibi, M.D., FACC. All rights reserved.

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Published by AuthorHouse 6/26/2015

ISBN: 978-1-5049-1427-7 (sc)

           978-1-5049-1428-4 (e)

Library of Congress Control Number: 2015909148

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FOREWORD

New technological developments,in all branches of human endeavors should be approached with an open mind, developed and utilized to the best for the benefit of humankind.

Not all new developments live up to their initial claims, many so-called new developments fall in disuse or oblivion after a period of time. Computed tomography or CT-angiography has stood the test of time, in various branches of medicine, but in the field of congenital heart disease, pediatric or adult, it has a special place which has not been reported to this date in a comprehensive manner.

The author (JGS) has been actively involved in congential heart disease since 1970, and has grown with his patients, observing their problems during their growth from infancy,to childhood and adulthood. In contrast to the rosy days of 1970s and 1980s, as these patients grew older, the complications of the palliative and corrective procedures became apparent and the diagnosis and corrective procedures became more complicated, necessitating a great deal of effort to secure solid information before embarking on second, third or fourth operations.

The standard method to approach congenital heart defects for diagnosis and operative procedures was cardiac catheterization and angiocardiography, however over the years, and especially the adolescents and adults with congenital heart defects posed major problems, which necessitated a new branch of specialty, unfortunately disconnecting the continuous comprehensive approach to adults with congenital heart disease. This disconnection is most disappointing, both as far as the patient and the physician are concerned. To be able to render the best service to the patient, the care must be continuous and comprehensive.

CT angiography is a very powerful method to approach these complex cases, which could be used only by cooperation between an experienced specialist in congenital heart defects and a radiologist, well-versed in her/his specialty, who is interested in this type of patients. Thus this new methodology needs special endeavor on the part of two disciplines. This is in contrast to other fields of its use in which a radiologist could easily tackle the problem and report to the referring physician without needing a joint review of the case and a search for proper answers.

It is the authors’ sincere wish that CT angiography be regarded as a major tool, besides cardiac catherization and angiocardiography in most cases, in initial and late evaluation of patients with congenital heart defects, especially the most complex cases, regardless of the patient’s age.Of course cardiac catherization and angiocardiography especially when pressure measurements are needed remain as indispensable methods of investigation.

The authors are greatly indebted to Dr H. Emami,director of the executive council of Day Hospital for his invaluable support.

We are thankful to The Ethics Committee of The Day Hospital for permission to publish the data included in this book.

We are grateful to Mr Bahram Rimaz, Mr Masood Jahanfada and Ms Massuma Shams the super-technicians of CT-angiography Department of Day Hopital for their superb technical assistance.

The last but not the least we wish to thanks Ms MacVand for her secretarial assistance.

JGS and MT

Table of Contents

FOREWORD

CHAPTER 1

BASIC TECHNICAL INFORMATION FOR CARDIOLOGIST USING CT ANGIOGRAPHY.

CHAPTER 2

APROACH TO CONGENITAL HEART DEFECTS BY CT ANGIOGRAPHY

STEP I: SEGMENTAL APROACH TO DIAGNOSIS OF CONGENITAL HEART DEFECTS.

CHAPTER 3

STEP II: IMPORTANT NEGATIVE FINDINGS

CHAPTER 4

STEP III: SPECIFIC ANOMALIES. CASE STUDIES

CHAPTER 5

REFERENCES

EPILOGUE

ABOUT THE AUTHORS

CHAPTER 1

BASIC TECHNICAL INFORMATION FOR CARDIOLOGIST USING CT ANGIOGRAPHY.

For technical, and theoretical information regarding computed tomography, and its application to the cardiovascular system ie CT angiocardiography major texts and references should be consulted (See Chapter 5: References). In this work we shall concerntrate on the method to diagnose congenital cardiovascular defects. However certain technical points are reviewed briefly.

Certain practical technical points are mentioned below:

1-The CT angios shown in this work were obtained by multidetector series computed tomography (MDCT). Data acquisition is spiral (helical) mode, 64-detector system are obtained per rotation.The manufacturerer is Siemens.

2-The contrast medium used for cardiovascular CT angio, is Iodixanol, trade name Visipaque. The dose used for infants and children is 1.5-2ml/kg given IV push.

3-If coronaries, root of the aorta, ventricular, atrial or cardiac valves have to be studied EKG-gated CT angios are obtained. However static organs like the aortic arch, pulmonary veins,pulmonary artery system etc, could be satisfactorily studied by non-EKG-gated image acquisition.

4-For infants an anesthesiologist versed in pediatric care is in attendance and Nesdonal or Ketalar is used for sedation. No medications are used to reduce the heart rate.

5- For studying fast-moving structures, ie coronaries, aortic root and ventricles EKG synchronization is necesssary.Thus for EKG-gated CT angiography, in adolescents and adults metoprolol is given 50-100 mg orally prior to the study. When the heart rate drops to the level of 60-65 beats/min data acquisition could be started.

6-For coronary artery disease,sublingual administration of nitroglycerin is recommended to improve visualization of the coronary arteries.

7-Arrhythmia artifacts, due to atrial fibrillation, premature ventricular or atrial contractions could be eliminated by synchronization with peak of R-waves, instead of RR-interval.

8- Some general remarks regarding radiation dose.

a-The radiation energy absorbed may be of various types: X rays, electron ie beta rays, neutrons, gamma rays,or other particles.

b-The radiation energy absorbed by the patient’s tissue or organ is important, not the radiation generated by the equipment.

c-Therefore the energy absorbed must be divided by the mass of the matter. The energy is expressed in joules and mass in kilogram. In the international System of quantities and units, one joule /1kg is the special unit called gray (Gy) for absorbed X-ray.

Older units for absorbed radiation energy are:

1 Gy = 100 rad; 1mGy = 0.1 rad.

d-Radiation weighting factor or constant. This unit is a dimensionless unit used for reporting the magnitude of the biological effects of different types of radiation. The type of radiation used, affects the value of the radiation weighting factor or constant. Radiation weighting factor or constant shows the absorbed dose in Gy averaged over an equivalent dose (given in sievert ie Sv).

Thus this relation is expressed as:

equivalent dose (Sv) = absorbed dose in tissue (Gy)x radiation weighting factor.

The older equivalent dose (Sv) was given in rem, thus : 1 Sv = 100 rem; 1 mSv=0.1 rem.

As X-ray is used, in CT angio, the radiation weighting factor is equal to 1.0. Therefore in CT angiography, the absorbed dose in a tissue, in Gy, is equal to the equivalent dose Sv.

For Computed Tomography,other special dose quantities are used.These are:

1-Computed Tomography Dose Index (CTDI)

2-weighted CTDI (CTDIW)

3-volume CTDI (CTDIVOL)

4-multiple scan average dose (MSAD)

5-dose-length product(DLP)

The radiation dose received by the patient during cardiac,eg coronary artery study varies greatly depending on the type of equipment, EKG-gated and nongated studies.The radiation dose in one double-blind, multicenter report ranged between 568-1259 mGy x cm. This median dose-length product (DLP) was 885 mGy x cm.The dose received increases depending on the patient’s weight, rhythm abnormalities and whether the study is EKG-gated or nongated .

See references under Radiation dose.

CHAPTER 2

APROACH TO CONGENITAL HEART DEFECTS BY CT ANGIOGRAPHY

METHODOLOGY

Using CT angio for proper decision-making and to guide the surgeon for corrective or palliative procedures while dealing with congenital heart defects, is quite safe, easy and comprehensive. However to achieve this goal certain preconditions must be osbserved.

The cardiologist in charge must know the patient in depth and must have history, and physical examination findings in detail. EKG, chest-X-ray and echocardiographic data must be studied and recorded in detail.These informations must be used while discussing the case with the radiologist, and answers to major questions as delineated below should be sought with utmost attention.

When reading CT-angios the cardiologist and the radiologist must sit together, and while knowing the pathology, the radiologist finds the pathology and both physicians study the case in depth. Once through with the joint conference a comprehensive report is made which although including the CT-angio findings, but also giving an overall picture of the patient and the pathology concerned. In this approach we report about the patient and the entire pathology concerned, not just a radiographic description of the images.

In almost all cases, the data are quite adequate for surgical management. Of course when catherization is needed for essential problems, such as pressure gradients, ie direct pressure