With its increased availability, technical speed, improved postprocessing software, and ease of patient throughput, the applications for cardiac multidetector computed tomography (MDCT) are growing.
is currently a Radiologist at Mercy Hospital Anderson,
Cincinnati, OH. He graduated summa cum laude from Saint Louis
University, St. Louis, MO, in 1997 and graduated from The
University of Cincinnati College of Medicine, in 2001. He
completed his Diagnostic Radiology Residency in 2006 at the
University of Cincinnati, where he served as Chief Resident. He
has been actively involved in research and has authored or
coauthored several abstracts, posters, and peer-reviewed
With its increased availability, technical speed, improved
postprocessing software, and ease of patient throughput, the
applications for cardiac multidetector computed tomography (MDCT)
continue to expand. The most widely publicized applications are
for the characterization of the coronary arteries. However, data
also exist to provide the clinician with a morphologic and
functional cardiac analysis, extending its scope and utility as a
noninvasive imaging modality.
With its increased availability, technical speed, improved
postprocessing software, and ease of patient throughput, the
applications for cardiac multidetector computed tomography (MDCT)
are growing. One of the most widely publicized uses is for the
evaluation of the patient with atypical chest pain, where it can
provide exquisite detail of the coronary arteries to allow for the
characterization of coronary artery plaque to help guide clinical
decision making for the cardiologist and primary-care physician.
Current imaging protocols also allow for the visualization of
cardiac morphology, which is becoming more useful for atrial
fibrillation (AF) treatment and for patients undergoing complex
cardiothoracic surgery. Data also exist to predict clinical
outcomes and monitor treatment response in patients.
Utility of visualizing morphology and its effects on
Visualizing cardiac morphology, particularly of the left atrium
(LA), is becoming increasingly important in patients with AF.
Through multivariate analysis, the Framingham study showed that
left atrial diameter is an independent risk factor for the
subsequent development of AF, with a hazard ratio of 1.39 for every
5-mm increase in size.
Determining atrial size may help provide insight into the
complications and sequelae of AF,
as studies have shown a relationship between atrial size and
with a stepwise increase in the rate of stroke for every 10-mm
Furthermore, there is an opinion that the larger the LA, the less
likelihood of remaining in sinus rhythm.
While the measurement of LA size by M-mode echocardiography is
widely used, it is inaccurate because it provides only a single
and the quality of the images is also dependant on the skill of the
echocardiographic technician and on the body habitus of the
Measurements of LA diameter can easily be obtained from MDCT images
without the technical limitations faced by echocardiography.
The applications of MDCT in preprocedural planning for the
treatment of AF are expanding. Preoperative evaluation of patients
prior to the Wolf mini-maze,
a minimally invasive thoracoscopic surgery for the treatment of AF,
is one such example.
In addition to excising the left atrial appendage, this procedure
involves isolating the pulmonary veins (Figure 1A), by placing a
radiofrequency device on the atrium medial to the pulmonary veins.
In addition to detecting coronary artery anomalies, performing MDCT
prior to the procedure can help detect several findings that can
affect the surgical approach, such as atrial appendage thrombus,
atypical course of the pulmonary veins (Figure 1B), and
pre-existing pulmonary vein stenosis from prior ablation attempts
(Figure 1C ).
Evaluating the morphology of the left atrial appendage is also
important, particularly as it relates to the detection of thrombus,
as the presence of thrombus or sluggish flow can increase the risk
of embolic stroke.
Transesophageal echocardiography (TEE) is the gold standard for the
detection of thrombus,
but false-positive results occur with TEE.
Mohrs et al
concluded that magnetic resonance imaging (MRI) lacks diagnostic
accuracy for the detection of a left atrial appendage thrombus.
With MDCT, the difficulties are in distinguishing thrombus from
sluggish flow (Figure 2) in the left atrial appendage, and this
decreases its specificity. However, the addition of a 60-second
delayed scan when performing MDCT can help improve the specificity
of the examination for thrombus (C. Meyer, MD, unpublished data,
In addition to revealing the pulmonary vein anatomy and
morphology of the LA, it is also important for the
electrophysiologist to determine the location of the esophagus with
respect to the LA prior to beginning a catheter-guided ablation
procedure for AF. The course of the esophagus varies along the
posterior LA atrium; however, Lemola et al
noted that in the majority of patients the esophagus is parallel to
the ostia of the left-sided pulmonary veins and in direct contact
with the posterior left atrium for >5 cm along its long axis.
The authors emphasized that the target sites during catheter
ablation of AF may often fall within this region of contact and
suggested that the presence of a fat pad around the esophagus
insulates it from thermal injury. Therefore, using CT to identify
patients who do not have this fat pad prior to the procedure could
Understanding the spatial relationship (Figure 3) can avoid the
potentially lethal complication of left atrial-esophageal fistula,
which can result in death in up to 50% of cases.
However, the mobility of the esophagus may necessitate real-time
imaging for an accurate awareness of the position of the esophagus
during ablation procedures.
Evaluating the morphology of the coronary venous anatomy (Figure
4) is also of interest to the clinician. Knowledge of the coronary
venous anatomy can help guide multiple therapies, including
catheter placement in the coronary sinus for ablation procedures,
placement of left ventricular (LV) or biventricular pacing devices
in patients with heart failure,
and the determination whether the venous system can be used to
bypass coronary artery stenoses for percutaneous in situ coronary
or used for retroperfusion therapy.
The current gold standard for imaging coronary veins is retrograde
venography via the coronary sinus.
However, recent reports have shown promising results for the use of
MDCT angiography as a tool for the visualization of the coronary
Clear delineation of cardiac morphology is also imperative for
the cardiac surgeon in cases of repeat sternotomy. Elahi et al
examined the complication rate in 185 patients who underwent repeat
sternotomy. They found complications directly attributable to
repeat sternotomy in 21 (11.3%) of the cases. These included minor
injuries to the aorta (4.8%), the right ventricle (RV) (3.2%), the
right atrium (1.0%), prior bypass grafts (1.0%), and the right lung
(0.5%). Most notably, there was uncontrollable hemorrhage from a
tear in the aorta (0.5%) and 3 deaths (2.6%). The overall mortality
in the repeat sternotomy group in the literature has been as high
After undergoing sternotomy, the anterior mediastinal anatomy
may be distorted by fibrosis. Major injuries may result in sternal
re-entry due to inadvertent laceration of the heart, coronary
arteries, or great vessels. Injury to implanted saphenous vein
grafts has been reported and can result in massive intraoperative
hemorrhage, myocardial ischemia, and infarction
(Figure 5). The lack of adequate retrosternal space is one of the
main risk factors for sternal re-entry.
This is of particular importance in patients with congenital heart
disease, such as Ebstein's anomaly (Figure 6).
If there is increased risk of damage to retrosternal structures
during sternotomy, the femoral vessels are commonly isolated prior
to the procedure. Partial cardiopulmonary bypass using the femoral
artery and vein is subsequently used to decompress the cardiac
chambers and cool the patient (circulatory arrest) prior to sternal
division. The presence of pseudoaneurysms (Figure 7) or the
enlargement or anterior displacement of the RV may be indications
for peripheral bypass.
In a study of patients who underwent preoperative cardiac MDCT for
planning of complex adult heart surgery, surgical management was
affected by the results of the CT scan in the majority of the
In patients with congenital heart disease, detecting coronary
artery anomalies prior to operative intervention is also
imperative. Detecting congenital coronary artery anomalies can
influence operative intervention in up to 60% of patients.
This is of particular importance in tetralogy of Fallot, in which
anomalous coronary artery vessels can cross the RV outflow track
and can interfere with its reconstruction.
Cardiac catheterization has always been considered the gold
standard for the delineation of coronary anatomy prior to complex
congenital heart surgery; however, Lee et al
recently reported the accuracy of MDCT in evaluating complex
congenital heart disease in neonates and suggested that MDCT could
replace diagnostic cardiac catheterization (Figure 8).
Assessing cardiac function
In patients with cardiac disorders, a desirable test to measure
function is one that can provide quick, accurate, reproducible, and
noninvasive high-quality images to determine the severity of
cardiac impairment and evaluate the efficacy of treatment.
In patients with ischemic heart disease, the ejection fraction (EF)
has been shown to be a more powerful predictive factor of clinical
outcome than the number of vessels involved.
Currently, cardiac function can be measured with ventriculography,
echocardiography, MRI, electrocardiographic (ECG)-gated
single-photon-emission CT (SPECT), electron-beam CT, and MDCT.
Conventional ventriculography to measure cardiac function, while
often considered the gold standard, is an expensive and invasive
modality performed during angiography. However, it is limited by
the geometric assumptions that are made from projectional images.
This can lead to the inability to evaluate regions of the heart
where there are complex irregular shape changes.
Transthoracic ECG (TTE) is widely used, as it can provide
accurate measurements of ventricular volumes and mass as a
bedside cardiac evaluation tool. However, TTE results are heavily
technician-dependant, and in approximately 10% of patients, the
endocardial borders cannot be well defined, in which case the
functional assessment depends on the operator's experience and
subjective visual perception.
The complex shape of the RV and its retro-sternal location also
make functional evaluations of the RV particularly difficult by
With its multiplanar nature and high spatial and contrast
resolution, MRI is likely the noninvasive standard of reference for
the qualitative assessment of ventricular volumes, EF, and mass.
Other advantages of MRI include the lack of radiation exposure and
the fact that it does not require injection of contrast media.
In addition to its increased cost, MRI does have limitations in
that it cannot be performed in patients with implantable devices
(such as pacemakers or defibrillators) and some MR sequences are
susceptible to irregular or changing heart rates.
Prolonged examination times in the supine position and repeated
breath-holds can be stressful for patients with breathing
difficulties and can lead to degradation of image quality.
Electrocardiographic-gated SPECT offers the ability of combining
3-dimensional (3D) assessments of LV volumes and consecutively
calculated function parameters.
Its accuracy is limited by its low spatial resolution, and the
definition of endocardial borders in patients with thinning after
infarction may be difficult because of low counts from these areas.
The need for repeated radionuclide doses is also problematic due to
; therefore, it remains a projection method, which means that it
provides less anatomic methods than competing modalities.
Electron-beam CT can provide a temporal resolution of 50 to 100
msec to produce a motion-free image of the heart in diastole,
but it is not widely available. However, the longitudinal
resolution in the z-axis is limited, which can impair 3D
visualization and ventricular volume calculation.
Multidetector CT can image the heart with high spatial and
temporal resolution in a single breath-hold with ECG
synchronization to provide high-quality 3D data sets for
postprocessing that can be used to measure cardiac function
without the use of geometric assumptions. Retrospective ECG gating
and cardiac software developments allow wall motion to be evaluated
and functional calculations to be made. The MDCT images should be
less susceptible to cardiac arrhythmias than MRI because of the
retrospective gating with MDCT versus the prospective gating with
Since MDCT is a true volumetric modality, enlarged or grossly
deformed hearts should not influence the accuracy of the
MDCT for the evaluation of cardiac function
Many functional measurements can be calculated after determining
the end-diastolic volume (EDV) and end-systolic volume (ESV). The
EF is defined as EF = EDV-ESV/EDV × 100% and has a normal range of
50% to 70%. The stroke volume (SV) is defined as SV= EDV-ESV, and
cardiac output (CO) can be derived when the heart rate (HR) is
considered CO = SV × HR. When the body surface area (BSA) is
considered, advanced calculations can be determined, including the
stroke index (SV/BSA) and the cardiac index (CO/BSA).
Like echocardiography and MRI, LV volume measurements are based
on short-axis reformations using Simpson's method. A diastolic and
systolic phase is needed for LV functional assessment, which is
usually found at the minimum ventricular diameter (25% of the R-R
interval) and the maximum ventricular diameter (85% of the R-R
Diastolic and systolic volumes can be calculated using MDCT
software in the end-diastolic and end-systolic phases. Epicardial
and endocardial contours can be drawn either manually or
automatically with cardiac software (Figure 9). Software packages
can calculate ventricular volume and wall thickness to help speed
analysis. Automated segmentation algorithms used in MDCT are
sensitive to adequate contrast opacification, as the delineation of
the trabeculae and thus the volume can be influenced by the degree
of contrast opacification.
For accurate volume calculation, the papillary muscles should be
excluded from the cav-ity.
The total electromechanical systole duration is approximately
300 msec, with the minimal ventricular volume being maintained for
only 80 to 200 msec.
A temporal resolution of 30 to 50 msec per scan is necessary to
image maximum systolic contraction. With the current repetition
time of 64-slice MDCT at 165 msec, the volume changes during rapid
ventricular filling and ejection are not well represented. While
plain volume has excellent agreement with MRI, the regional
functional analysis is limited, as there may be a slight
overestimation of LV ESV by MDCT compared with MRI, which can
result in an underestimation of LV EF from 1% to 7%.
However, the reproducibility of global functional parameters is in
the range of other modalities and is close to that of MRI, which is
accepted as the reference method for precise quantitative LV
functional analysis for LV EDV and LV ESV.
The evaluation of RV function is also important, particularly as
it relates to the outcomes of patients with acute pulmonary
since RV failure is the main cause of death within 30 days.
Assessing RV function is important in identifying high-risk
patients so the appropriate therapy can be initiated. Also, RV
has implications in congenital heart diseases involving the RV and
chronic heart failure.
Recently, it has been shown that RV systolic function can be
accurately assessed using ECG-gated MDCT data
; however, MRI is still accepted as the gold standard for measuring
When compared with MRI, MDCT offers a smaller variance in RV
volumetric measurements. This is likely a direct result of the
single breath-hold technique for MDCT rather than the multiple
breath-hold MRI technique. Furthermore, estimates of RV EF
calculated retrospectively from ECG-gated MDCT were found to be
similar with scintigraphy and were accurate in patients with known
or suspected RV dysfunction.
If functional parameters are to be measured, delineation of the
right cardiac chambers is improved with a biphasic injection or
with the administration of dilute contrast after the initial bolus
In addition to evaluating LV and RV fraction, the left atrial EF
can also be assessed by measurements of the EDV and ESV. A recent
report highlighted the importance of left atrial EF as it relates
to left atrial transport function. Lemola et al
found that the restoration of sinus rhythm by left atrial catheter
ablation compromised left atrial systolic function, which suggests
that the loss of contractile function was likely related to the
amount of tissue that was ablated. After catheter ablation therapy,
the left atrial EF was similar in patients with paroxysmal AF and
in those with chronic AF who were in sinus rhythm, but it was noted
that the LA function in these 2 groups was lower than in control
subjects with no history of AF.
In addition to EF, a recent review defined the important
parameters involved in assessing cardiac function.
Wall motion can be defined as the displacement of the points from
the end-diastolic phase to the end-systolic phase. Wall thickening
is indicative of the regional percentage of wall thickening during
the systolic phase and is the single most accurate measurement of
local function, since endocardial wall motion can be difficult to
assess accurately in patients with ischemic heart disease. Regional
EF expresses the EF relative to a specific region or segment of
myocardium. A semi-quantitative estimation of these regional
parameters can be performed using color polar maps. The bull's-eye
pattern based on the 17segment approach of the American Heart
Association should be used
If regional wall motion is to be displayed, at least 10 to 20
heart phases are needed.
Images can be viewed in a cine loop to qualitatively assess LV wall
motion. Normal contraction requires functional tissue with adequate
blood supply, and the reduction of blood flow below a critical
threshold prevents normal contraction.
A hypokinetic segment is defined as impaired contraction,
akinesis is when there is no motion, and dyskinesis is the
paradoxical outward motion in systolic contraction. Generalized
wall motion abnormalities occur in dilated cardiomyopathy and
end-stage valvular heart disease; however, regional wall motion
abnormalities occur in ischemic heart disease.
Functional analysis requires that no medication be administered
before the MDCT examination that could influence the patient's
heart, since an artificially reduced heart rate may alter the
functional parameters. The use of dual-source CT may potentially
diminish the need for beta-blockers and improve volume and EF
Short-axis images are readily available in MRI, and
time-consuming secondary cardiac reformations in cardiac MDCT are
not required. The total evaluation time of MDCT functional analysis
has become the focus of recent studies, and reported evaluation
times range from 30 to 50 minutes for 4-channel MDCT
and 14 to 20 minutes for 16-channel MDCT.
Costs of evaluating cardiac morphology and
The cost effectiveness of the assessment of cardiac morphology
and function with examinations must also be considered. For fiscal
year 2007, our hospital charges for the examinations are as follows
(CPT codes noted): $2821 for a cardiac MRI with contrast (75553),
$2166 for a cardiac CT without calcium score (0148T/76497), $812
for 2-dimensional TTE (93307), and $2025 for a myocardial perfusion
SPECT scan (78465).
While the cost of cardiac MDCT is high, and there is a trade-off
of radiation dose, it offers the benefit to the patient of
detecting other abnormalities in the thorax that would not be seen
by other modalities (Figure 12). Extracardiac findings can be
detected in up to 24% of patients, and nearly 5% of these may be
major findings such as lung carcinoma and pulmonary emboli.
Cardiac MDCT is a valuable clinical tool for the evaluation of
cardiac morphology and function. In patients with atrial
fibrillation or those undergoing open heart surgery, it is a
valuable tool that can clearly delineate the relationship of native
coronary arteries, coronary artery bypass grafts, and the cardiac
chambers to the sternum and mediastinal structures. Armed with this
spatial knowledge, the surgical approach may be altered to avoid
potential complications related to prior surgery, chamber dilation,
or mass effect. While it is not the first-line modality for
evaluating cardiac function, MDCT can also evaluate cardiac
function and wall motion in conjunction with a CT angiogram, and it
offers the added benefit of detecting clinically significant
abnormalities in the thorax. Therefore, the clinician can derive a
great deal of accurate diagnostic and clinically useful information
in a study that can be performed quickly.
The author would like to thank Rhonda Strunk, RT(R)(CT) and
Cristoper Meyer, MD, for their help and support.