At first glance, humans and dogs have very different lifespans and hearts. Yet both can develop the same life-threatening condition: dilated cardiomyopathy( DCM). Despite the obvious differences, DCM affects both species in surprisingly similar ways— a striking example of how shared biology can lead to shared disease.
DCM is a cardiovascular disease and a major cause of heart failure and sudden death in people and dogs alike. It accounts for roughly 10 % of cardiac diagnoses in dogs, making it the second most common form of heart disease in the species, and it is the third most common inherited heart disease in people, with an estimated prevalence of 35.6 per 100,000.
Clinical characteristics
DCM is defined by an enlarged ventricular chamber as the muscle dilates, together with systolic dysfunction— when the left ventricle, the heart’ s strongest pumping chamber, becomes weak and cannot contract effectively, reducing blood flow to the body. Dilation reduces the muscle’ s contractility, causing incomplete emptying and increasing end-systolic volume( the blood left at the end of a contraction). That raises stress on the ventricular wall, promoting further dilation and worsening systolic dysfunction.
In people, the causes are complex: genetic factors, myocardial ischaemia, hypertension, toxins, infections and metabolic defects. In dogs, DCM is more often linked to genetic predisposition, nutritional deficiencies and infections, though it usually remains idiopathic( unknown). Diet is a crucial environmental factor in dogs: grain-free or legume-rich diets have been associated with DCM, often involving a deficiency of taurine( an amino sulfonic acid)— and in some dogs this is reversible with the right dietary changes.
How the disease progresses
Both human and canine DCM progress through phases, beginning with an asymptomatic period in which functional changes occur at the cellular and molecular level without producing symptoms. The individual still appears healthy, even as electrical and morphological changes set in. Chronic DCM then activates two major neurohormonal systems: the sympathetic nervous system( SNS) and the renin – angiotensin – aldosterone system( RAAS).
The SNS releases catecholamines such as adrenaline, raising heart rate, contractility and vasoconstriction to maintain blood pressure and perfusion— but in the long term this causes progressive myocardial injury and deteriorating systolic function. The RAAS releases renin, leading to angiotensin II, which drives vasoconstriction and aldosterone release, causing sodium and water retention and raising blood volume. Helpful at first, this too becomes harmful: increased ventricular stress, myocardial fibrosis( scarring), ventricular remodelling and electrolyte imbalance. The result is a vicious cycle— reduced contractility triggers SNS and RAAS responses that briefly aid circulation but ultimately accelerate myocardial damage and reduce cardiac output.
DCM is a powerful example of how shared biology can lead to shared disease.
A 24-hour Holter monitor can detect the electrical changes; individuals who go on to develop DCM often show ventricular arrhythmias— abnormal rhythms originating in the ventricles— which can cause sudden death independently of heart failure, particularly in dogs. Echocardiography can reveal left-ventricular enlargement, signalling symptomatic disease. Because this phase is asymptomatic, a dog may have DCM for years without obvious signs, allowing the disease to weaken and enlarge the heart more severely over time.
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