RAMB Março/Abril 2016

oreira

LAR

194

ssoc

ras

2016; 62(2):192-196

plantation, as well as higher mortality in the short and

long-term.

Many surgeons declare that they are discour-

aged from using the internal thoracic arteries as a graft

in patients with a history of chest radiation; however, the

clinical course is comparable, in the medium term, to pa-

tients with no history of irradiation.

amage

the myocardium

Clinical manifestations of cardiovascular injury due to

RT often take many years, if not decades, to manifest.

However, sub-clinical lesions have been identified within

six months of the end of treatment.

25,28

Myocardial dam-

age has been identified early through scintigraphic stud-

ies with images of myocardial perfusion performed six

months after RT in patients treated for left breast CA.

Currently, RT techniques with tangential photon beams

are used with prior planning using three-dimensional

computed tomography in order to minimize such dam-

age. However, any dose of radiation always affects the

heart, mainly in the anterior wall of the left ventricle.

25,28

Perfusion defects are found in approximately 40% of pa-

tients 6 to 24 months after RT for left breast CA and these

defects are more prevalent in patients with a higher heart

volume within the radiation field.

Perfusion defects after irradiation of a small fraction

of the myocardium are caused by damage to the microvas-

culature. Ionizing radiation causes damage to the endo-

thelial cells of the capillaries with consequent capillary ede-

ma, obstruction of the lumen of the vessel and subsequent

myocardial fibrosis,

as a result this leads to sub-clinical

functional abnormality of the left ventricle.

In addition

to the microvascular damage, there is also direct damage

from the radiation over the cardiomyocytes.

In histopath-

ological studies, the most common microscopic fibrosis

patterns are pericellular and perivascular. Pericellular in-

terstitial fibrosis findings support the hypothesis of early

capillary damage causing diffuse ischemia and fibrosis.

A high frequency of diastolic dysfunction of the left

ventricle has been demonstrated by echocardiography in

asymptomatic patients who have received at least 35Gy

of mediastinal irradiation for treatment of Hodgkin’s dis-

ease. Diastolic dysfunction is explained via histopathol-

ogy demonstrating fibrosis resulting frommicrovascular

damage. Ischemia induced by cardiac stress tests are more

common in these patients and probably CAD is also in-

volved as a cause of diastolic dysfunction associated with

significant morbidity.

29,30

Less frequent than diastolic dys-

function, left ventricular systolic dysfunction is also re-

ported at higher than expected frequency in patients with

a history of RT, even if asymptomatic.

14,31

alvular

damage

Valvular damage is often found in patients undergoing

chest RT probably due to direct damage from the radia-

tion on valvular tissue, since they are not vascularized. The

lesions are characterized by diffuse fibrosis of the cusps,

with or without calcification.

Initially there is a valvular

thickening without clinical repercussions that can be iden-

tified by echocardiography in the first decade after RT. It

affects one or more valves and evolves gradually, either

through worsening of pre-existing damage or appearance

of new damage.

Clinically significant valvular dysfunc-

tion has been described, on average, 22 years after RT in

survivors of Hodgkin’s disease.

Consistently, more severe

valvular lesions are present on the left side of the heart

valves, as these areas have increased hemodynamic stress.

Aortic stenosis is the predominant lesion.

14,15,33

lectrical

and

conduction

system

disturbances

As already described for other tissues, radiation also causes

damage and scarring to the conduction system. Chang-

es in the electrocardiogram such as conduction defects,

T wave abnormalities and arrhythmias have been report-

ed and may indicate myocardial damage or damage di-

rectly to the conduction system. The right branch block

is more commonly observed than the left. The initial

changes can develop into complete atrioventricular block,

suggesting progressive damage.

24,30,34,35

Among the ven-

tricular repolarization abnormalities, electrocardiograph-

ic changes that have been observed are T-wave flattening,

deformity or inversion, with higher incidence six months

after RT. These changes present greater magnitude in the

precordial derivations.

hanges

the

carotid

arteries

and

other

vessels

An increased risk of stroke secondary to carotid artery dis-

ease has been reported in patients with a history of cervi-

cal irradiation, especially when it occurs at an age group

in which the atherosclerotic disease of the carotid artery

would not be expected.

15,37

A study that used a duplex scan

of the carotid arteries in patients between 18 and 37 years

of age who received cervical RT due Hodgkin’s lymphoma,

all in remission and asymptomatic, with more than five

years since the end of treatment compared with a control

group of healthy and age-matched volunteers identified

focal or generalized abnormalities of the

intima

-media lay-

er (26% in the study group versus 3% in the control group),

such as fatty streaks, irregularities and discontinuities in

the layers, microcalcifications, graininess and initial plaques