CARDIAC INVOLVEMENT IN THE ACUTE PHASE OF KAWASAKI DISEASE
Vikas Kohli *
Department of Pediatrics.*
Kawasaki disease diagnosis lies in a high index of suspicion in children with fever with a constellation of findings. The long-term prognosis is not affected by the arthropathy or the dermatological involvement. It is clearly the cardiac issues that affect the long-term outcome, life span and subsequent quality of life.

Cardiac assessment is critical to the complete diagnosis and there are set guidelines by which an echocardiogram should be done for completing the evaluation. A pediatric echocardiographer with experience in evaluating all the branches of coronary arteries critically in addition to a good echo window and a well sedated child are essential pre-requisites for the complete evaluation. The visualization of a single aneurysm does not conclude the study since others may co-exist.

Index of Suspicion, Incidence & Cardiac Involvement:

Cardiac evaluation begins with the history, which in addition to the criteria and additional clinical and laboratory data (Table 1) may suggest pericarditis, myocarditis or valvular involvement; though, most commonly, cardiac involvement is not suggested by the history. Late presentation, which is not uncommon since Kawasaki is a rare diagnosis in India, is the most common historical clue to the presence of aneurysms in the coronary arteries. Delay in diagnosis results in higher cardiac involvement and a further increase in the mortality. Japan (the country with the highest incidence) has the lowest mortality rate. In 1970's, the mortality decreased to 1-2% and more recently has been reported to be 0.08% from Japan. The mortality remains much higher in other countries with a lower incidence (thereby a decreased awareness and a possible delay in diagnosis) are 6% in New Zealand, 2% in Sweden and 3.7% in The British Isles.

Coronary Aneurysms - Echocardiographic Diagnosis:

Two-dimensional echocardiographic examination includes display of the left main, anterior descending, and left circumflex coronary arteries as well as the proximal, middle, and distal segments of the right coronary artery and the posterior descending coronary artery. These vessels are visualized in multiple planes using a combination of parasternal long-axis and short-axis and apical four-chamber and two-chamber views, as well as subcostal long and short axis projections. The diagnosis of normal coronary artery anatomy should not be made until all major coronary artery segments have been visualized and judged to be normal. The cardiac ultrasound examination should be performed using transducers with the highest frequency possible. This typically requires a 7.5-mHz probe in infants, a 5.0-mHz probe in toddlers, and a 3.5-mHz or 5-mHz probe in older children. Display of coronary artery anatomy is facilitated by the normal translational movement of the heart.

Evaluation of coronary artery morphology should include quantitative or qualitative assessment of the inner diameters of the vessels. Configuration and number of aneurysms and the presence or absence of intraluminal or mural thrombi should also be assessed. Aneurysms are identified as saccular (nearly equal axial and lateral diameters) or fusiform (symmetric segmental dilatation with gradual proximal and distal tapering). When the coronary artery diameter is larger than normal but a segmental aneurysm is not apparent the vessel is described as ecstatic. Care must be taken in making the diagnosis of ectasia because of considerable normal variation in coronary artery distribution and dominance. Aneurysms are classified as small (less than 5 mm in internal diameter), medium (5 to 8 mm in internal diameter), or giant (more than 8 mm in internal diameter).

Coronary Aneurysms - Incidence & Outcome:

Historically when Kawasaki disease was first described, children would get better and then start getting sicker and subsequently die in the 3 to 5 week - now we know it was from the coronary artery thrombosis.

Up to 20-25% of untreated patients develop coronary aneurysms, usually after the 10th day of illness. The cardiac illness peaks by the 4th week and saccular or fusiform aneurysms can form by the 18 to 25 day of onset of illness.

Though coronary aneurysms may be detected early, the fate of the aneurysms is different. When patients with Kawasaki underwent angiography, 1-3 months after the illness, 15% were noted to have an aneurysm. On repeating the angiogram 5-18 months later, 50% of these had resolved while 50% persisted. Of those which persisted: half of them grew smaller, a third resolved though with stenosis and less than one fifth had coronary wall irregularities without stenosis.

Late and long-term follow-up showed 10-20 years later, more stenosis developed in more patients. The incidence of Myocardial Infarctions is reported as 39% of those with aneurysms or 19% of all patients. In most patients, coronary ectasia or aneurysms regress within 1 to 2 years. Approximately 1% of patients who recover from acute Kawasaki disease will develop giant coronary artery aneurysms or coronary artery obstruction due to thrombosis or stenosis.

Once aneurysms have been detected, the treatment given is aimed towards preventing thrombosis within the coronary artery. The true objective of management of a Kawasaki disease is early diagnosis and prevention of formation of coronary arteries.

Management Based on Risk Stratification:

Clinical experience with Kawasaki disease permits stratification of patients according to relative risk of myocardial ischemia. Risk level categories are listed below and are summarized in Table 3.

This stratification allows for patient management to be individualized with respect to (1) medical therapy to reduce the risk of thrombosis, (2) physical activity, (3) frequency of clinical follow-up and diagnostic testing, and (4) indications for cardiac catheterization and coronary angiography. Patients with no coronary artery changes on echocardiography at any stage of the illness seem to have no greater risk of future coronary arterial disease than the general population, but longitudinal studies are necessary to test this observation. The risk level for a given patient with coronary arterial involvement may change over time because of changes in coronary artery morphology. For example, regression of aneurysms is assumed to reduce the risk of myocardial ischemia. On the other hand, development of thrombosis or stenosis related to an aneurysm increases the risk.

For patients at certain risk levels, long-term antiplatelet therapy with aspirin is recommended. Some physicians combine aspirin and dipyridamole for antiplatelet therapy, although there are currently no data to support the efficacy of this regimen.
Risk Levels
Risk Level I: Patients with no coronary artery changes on echocardiography at any stage of the illness.

Risk Level II: Patients with transient coronary artery ectasia (disappears during the acute illness) on echocardiography.

Risk Level III: Patients with a small to medium solitary coronary artery aneurysm on echocardiography or angiography.

Risk Level IV: Patients with one or more giant coronary artery aneurysms or multiple small to medium aneurysms, without obstruction by echocardiography, preferably confirmed by coronary angiography.

Risk Level V: Patients with coronary artery obstruction confirmed by angiography.

Long-term management of patients with Kawasaki disease depends on the degree of coronary arterial involvement. Follow-up of a patient with coronary arterial aneurysms must be adapted to his or her clinical course and severity of the lesions. In all but a few patients, repeat cardiac ultrasound examination may be performed 6 to 8 weeks after the onset of illness if there has been no evidence of giant coronary artery aneurysms or thrombus formation and if clinical and laboratory sings of systemic inflammation have resolved. Follow-up echocardiographic examinations should identify progression or regression of aneurysms, and focal narrowing at the proximal and distal ends of an aneurysm should be noted. The physician may choose to perform an electrocardiogram when the echocardiographic study is done. A small subset of children with Kawasaki disease have valvar involvement; during follow-up examination of these children the possibility of mitral or aortic regurgitation should be considered.

Longitudinal follow-up of all patients begins 10 to 14 days after the onset of illness. In a great majority of patients who will develop coronary artery aneurysms, early signs of aneurysm formation are apparent at this time. In the absence of giant coronary arterial aneurysms or intraluminal coronary thrombi, repeat cardiac ultrasound examination may be performed 6 to 8 weeks after the onset of illness, when clinical and laboratory signs of systemic inflammation have subsided. Subsequent cardiac ultrasound studies for patients with no coronary arterial involvement or with ectasia or a solitary small aneurysm are performed 6 to 12 months after the onset of acute illness.

Table

Format for Reporting of Kawasaki Coronary Aneurysms/Ectasia
Echocardiographic Reporting of Coronary Arteries in Kawasaki Disease should include:
  1. Quantitative assessment of the coronary artery inner diameters
  2. Configuration of aneurysms: Saccular, Fusiform, Focal
  3. Number of aneurysms
  4. Areas of Ectasia: Coronary wall irregularity with dilatation
  5. Classification of the Aneurysms: small, moderate, large
  6. Any area of stenosis
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