Fig.11.25 ).Becauseofthewallthinningthataccompaniesdilation,theventricularthicknessmaybelessthan,equalto,orgreaterthannormal.Mural thrombi areoftenpresentandmaybeasourceofthromboemboli.Bydefinition,valvularandvascularlesions(e.g.,atheroscleroticcoronaryarterydisease)thatcancausecardiacdilationsecondarilyareabsent.
ThecharacteristichistologicabnormalitiesinDCMarenonspecific.Mostmyocytesexhibithypertrophy withenlargednuclei,butmanyareattenuated,stretched,andirregular.Thereisalsovariableinterstitialandendocardialfibrosis,withscatteredareasofreplacementfibrosis;thelattermarkpreviousmyocyteischemicnecrosiscausedbyhypoperfusion,ortheymaybethefootprintsofaprevious“missed”myocarditis.
InDCMsecondarytoironoverload,thereisamarkedaccumulationofintramyocardialhemosiderin,whichisdemonstrablebystainingwithPrussianblue.
The fundamental defect in DCM is ineffective contraction. Thus, in end-stage DCM, the cardiac ejection fraction typically is less than 25% (normal is 50% to 65%). Secondary mitral regurgitation and abnormal cardiac rhythms are common, and embolism from intracardiac (mural) thrombi can occur. DCM most commonly is diagnosed between 20 and 50 years of age. It typically manifests with signs of slowly progressive CHF, including dyspnea, easy fatigability, and poor exertional capacity. One half of patients die within 2 years and only 25% survive longer than 5 years; death is usually due to progressive cardiac failure or arrhythmia. Cardiac transplantation is the only definitive treatment, although implantation of long-term ventricular assist devices is increasingly utilized; in some patients, a course of mechanical assistance can produce durable regression of cardiac dysfunction.
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Fig. 11.25 Dilatedcardiomyopathy(DCM).(A)Four-chamberdilationandhypertrophyareevident.Asmallmuralthrombuscanbeseenattheapexoftheleftventricle(arrow).(B)ThenonspecifichistologicpictureintypicalDCM,withmyocytehypertrophyandinterstitialfibrosis.(Collagenisblue inthisMassontrichrome–stainedpreparation.)
Arrhythmogenic right ventricular cardiomyopathy is an autosomal dominant disorder that classically manifests with right-sided heart failure and rhythm disturbances, which can cause sudden cardiac death. Its prevalence in the general adult population is close to 1 in 5000 in a study from Italy. Similar prevalence is likely in the US where it seems to be under reported. Almost 10% of cases of sudden deaths in athletes have been ascribed to this entity. Morphologically, the right ventricular wall is severely thinned owing to myocyte replacement by fatty infiltration and lesser amounts of fibrosis (
Fig. 11.26 ). Many of the causative mutations involve genes encoding desmosomal junctional proteins at the intercalated disk (e.g., plakoglobin), as well as proteins that interact with the desmosome (e.g., the intermediate filament desmin). It’s thought that myocyte death is caused by desmosomal detachment, particularly during strenuous exercise.