**Echocardiography in Kawasaki Disease**

Deane Yim, David Burgner and Michael Cheung

*Department of Cardiology, Royal Children's Hospital and Murdoch Childrens Research Institute, Heart Research Group, Melbourne Australia* 

## **1. Introduction**

Kawasaki disease is an acute childhood systemic vasculitis characterised by a number of clinical features, with a predilection for damage to the coronary arteries. It predominantly affects children between the ages of 6 months to 4 years, although cases at either extreme of childhood are well described and are recognised to be associated with a greater risk of delayed diagnosis and treatment (Harnden et al., 2009; Pannaraj et al., 2004). There is a male predominance with a male to female ratio of 1.6 to 1. Despite important research progress since its first description in 1967 (Kawasaki, 1967), the aetiology remains unknown and there is no diagnostic test. The timely use of intravenous immunoglobulin has reduced the incidence of coronary artery lesions from 25% to 2-4% (Newburger et al., 2004). Transthoracic echocardiography is recommended in suspected cases of KD, however a normal study does not exclude the diagnosis.

#### **2. Incidence**

Kawasaki disease is the most common cause of paediatric acquired heart disease (Taubert et al., 1991). The incidence has been rising in both developed (Japan, Korea and United Kingdom) and rapidly industrialising countries such as India, which may reflect both a genuine increase and increased recognition (Krishnakumar & Mathews, 2006). The highest annual incidence is reported in Japan (218 per 100000 children <5 years of age) and Korea (113 per 100000 <5 years) (Nakamura et al., 2010; Park et al., 2011). The incidence is lower in Australia (3.7 per 100000 <5 years) but this data is 15 years old (Royle et al., 1998); given the rising incidence in other countries these rates may be an underestimate of true disease burden. Current epidemiological research is in progress in Western Australia, and these data will provide an updated incidence for Australia children.

### **3. Aetiology**

The high incidence of Kawasaki disease in Asian populations and increased risk in families and siblings suggests a genetic predisposition (Fujita et al., 1989; Uehara et al., 2003). Seasonal patterns are well recognised, with peaks in winter and spring in Australia, the United States and Europe and spring to summer peaks in Korea and China (Burgner &

Echocardiography in Kawasaki Disease 141

Kawasaki disease shock syndrome has been recently described and is characterised by hypotension and haemodynamic instability, often requiring intensive care. (Dominguez et al., 2008; Yim et al., 2010) These patients may be at increased risk of delayed diagnosis and treatment, refractory disease and more severe coronary artery involvement (Kanegaye et al.,

Transthoracic echocardiography is highly sensitive and specific for the diagnosis of coronary artery involvement and should be performed in confirmed or suspected cases of Kawasaki disease at the time of diagnosis. It is important to ensure that the timing or results of the echocardiogram do not delay initial treatment of Kawasaki disease, and that the diagnosis is made predominantly on clinical findings. On the other hand, if full criteria are not met and coronary artery abnormalities are present on echocardiography, then the child has incomplete features of Kawasaki disease and treatment with high dose intravenous immunoglobulin should be considered. The American Heart Association consensus guidelines provide a schema for the incorporation of echocardiography into the diagnostic process in children with possible incomplete Kawasaki disease (Newburger et

The primary aim of echocardiography is to identify coronary artery involvement, pericarditis and/or myocarditis. As always, optimising machine settings, using the highest possible frequency transducer and reducing two-dimensional gain and compression can achieve better image quality and resolution. B-mode cine loops and still frame images are necessary to assess coronary artery calibre, along with colour Doppler imaging set at a low Nyquist limit for evaluating normal coronary artery diastolic flow. Sedation may be necessary in children who are too irritable to tolerate a detailed study; our preference is to use 50-100mg/kg of chloral hydrate (max 1g) given orally with heart rate and peripheral

Coronary arteries should be assessed in multiple imaging planes before a decision is reached about the presence or absence of coronary artery abnormalities. The parasternal short axis view with or without a clockwise rotation of the transducer allows for imaging of the left coronary artery origin, left anterior descending artery and left circumflex artery, as well as the right coronary artery origin and proximal course. Parasternal long axis views with sweeps between the aorta and pulmonary artery will delineate the left main coronary artery, left anterior descending and circumflex arteries. Subcostal views are helpful for assessing the left circumflex artery and the mid-course of the right coronary artery. Apical four chamber views will show the length of the left circumflex artery and distal right coronary artery in the left and right atrioventricular grooves respectively. Coronary artery measurements should be taken from the inner edge to inner edge of the vessel wall and

2009).

al., 2004).

**6. Echocardiography in Kawasaki disease** 

**7. Principles of echocardiographic assessment** 

should not be measured at the level of normal branching.

**7.1 Optimisation of imaging modalities** 

oxygen saturation monitoring.

**7.2 Coronary artery assessment** 

Harnden, 2005). The epidemiology of Kawasaki disease, clustering of cases, community outbreaks and epidemics in the 1980s, support the hypothesis that an unknown infectious agent (or agents) triggers an abnormal inflammatory response in genetically susceptible individuals. Both conventional antigens and bacterial superantigens have been implicated as causative triggers in Kawasaki disease, however the triggering pathogen(s) remain unknown.
