Cardiovascular Journal of Africa: Vol 29 No 3 (May/Junel 2018)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 3, May/June 2018

AFRICA

135

Editorial

Cardiovascular magnetic resonance imaging in

rheumatic heart disease

NAB Ntusi

Rheumatic heart disease (RHD), a sequela of pharyngeal and

skin infection with group A

-haemolytic

Streptococcus

, affects

approximately 33 million persons globally, with low- and middle-

income countries (LMICs) disproportionately more affected.

RHD globally contributes the largest share to cardiovascular

mortality in individuals under 50 years old.

Sub-Saharan Africa

(SSA) bears the greatest burden of cardiovascular morbidity and

mortality related to RHD.

In highly endemic parts of SSA, the

prevalence of RHD ranges from 4.6 to 21.7 per 1 000 individuals,

based on echocardiographic screening.

Complications secondary to RHD cause disability-adjusted

life-years (DALYs) of 142.6 per 100 000 individuals globally,

translating to 0.43% of total global DALYs.

The rate of DALYs

attributable to RHD is highest in SSA, where it negatively affects

young and economically active members of the population.

Multiple cardiovascular imaging modalities are important for

the assessment of CVD andmany are entrenched into the modern

practice of cardiovascular medicine (Fig. 1). Cardiovascular

magnetic resonance (CMR) is the gold-standard technique

for many indications. It permits, in a single examination,

comprehensive characterisation of functional, morphological,

metabolic, tissue and haemodynamic sequelae of cardiovascular

pathologies (Fig. 2).

The high spatial and temporal resolution

of CMR, coupled with excellent tissue contrast enables complete

assessment of multiple parameters without exposure to ionising

radiation. Further, the ability to obtain images in any tomographic

plane regardless of body habitus confers significant advantage in

patients with limited sonographic acoustic windows.

CMR creates images from atomic nuclei with uneven spin

using radiofrequency pulses in the presence of a powerful

magnetic field. Hydrogen, which is abundant in fat and water,

is the most commonly used atom for MR imaging; and

tissue contrast in CMR is accounted for by three important

parameters: T1 and T2 relaxation and proton density. CMR is

safe, especially when compared with X-ray-based techniques.

The main MR contrast agent, gadolinium, has been shown to

be safe in millions of patients who have received it over decades,

and nephrogenic systemic sclerosis has not been reported with

the newer macrocyclic gadolinium-based agents, which are

preferentially used in patients with renal dysfunction due to the

high risk posed by iodinated contrast agents.

6,7

Characterisation of myocardial tissue is a unique feature

of CMR, traditionally achieved through late gadolinium

enhancement (LGE) imaging, and based on the relative difference

in volume of distribution of intravenously administered

gadolinium [and subsequent alteration of longitudinal relaxation

(T1) times] between normal and abnormal myocardium.

Hence,

LGE-CMR permits identification of focal fibrosis. More

recently, native (pre-contrast) T1 and T2 mapping techniques

have allowed direct measurement of myocardial relaxation times

on a pixel-wise basis, parameters which have been extensively

validated, offering similar diagnostic performance and superior

sensitivity for inflammation, infiltration, acute injury and fibrosis,

compared with delayed enhancement imaging in detecting

myocardial pathology.

Post-contrast T1 mapping and estimation

of the extracellular volume (ECV) allow for the assessment of

the degree of diffuse myocardial fibrosis.

Echocardiographic studies of RHD are established in clinical

practice and are indispensable for the comprehensive assessment

of valve lesions secondary to RHD, through confirmation of

aetiology of the valvular lesion and exclusion of non-rheumatic

causes of valve lesions. M-mode and two-dimensional cross-

sectional echocardiography are important for the assessment

of chamber size and function, diastolic dysfunction, valve

morphology and function, and both atrial and myocardial

remodelling. Colour-flow Doppler evaluates flow across valves

and can assess the haemodynamic effects of both stenotic and

regurgitant lesions.

Furthermore, serial echocardiography is important for

monitoring of disease progress as well as efficacy of surgical

repair or replacement. The use of strain imaging and three-

dimensional echocardiography is important for risk stratification

and in planning and predicting surgical outcomes.

Portable

echocardiography plays a crucial role in screening for RHD

and is important for defining disease burden, clarifying referral

pathways and informing policy for scaling up RHD control

programmes. The publication of the World Health Federation

criteria for the echocardiographic diagnosis of RHD in 2012

has provided standardisation and improved both specificity and

utility of echocardiographic screening for RHD.

CMR has been demonstrated to be capable of performing

many of the applications described above.

Multiparametric

CMR has been employed in small case series and case reports

in the diagnosis and guidance of management of patients with

RHD. In a series of three patients with chronic RHD, CMR

was found to be associated with LGE in atrial walls.

Using

Division of Cardiology, Department of Medicine,

University of Cape Town and Groote Schuur Hospital;

Cape Universities Body Imaging Centre, Faculty of

Health Sciences, University of Cape Town; Hatter Institute

of Cardiovascular Research in Africa, Department of

Medicine, University of Cape Town, South Africa

NAB Ntusi, FCP (SA), DPhil, MD,

ntobeko.ntusi@uct.ac.za