The DCM is differentiated in 3 development phases.
In Phase 1, the cell phase, the affected dog doesn’t show any symptoms. The auscultation, the X-ray and the echocardiography are also inconspicuous – you can see a normal heart with normal heart activity. At this time, the DCM can only be detected via a biopsy of the heart muscle. In a biopsy one would then identify the change in heart muscle cells (DCM1 or DCM2).
Also in Phase 2, the occult or subclinical phase, the affected dog does not show any externally recognizable symptoms. However, in this phase, the DCM is diagnosed via 24-hour ECG and echocardiography. The Collegium Cardiologicum e.V. usually uses a 'scoring' system based on breed-specific 'cut-off' values. The occult phase can last individually between 2 and 6 years. The occurrence of short periods of fainting attacks (syncopes) due to a cardiogenic (from the heart) reduction of the blood flow of the brain is not atypical in this phase. Sudden cardiac death can also occur, which at the present time cannot certainly be predicted. Only a ventricular tachycardia (increased heart rate, which comes from the heart chambers) in the 24-hour ECG is considered highly suspected for sudden cardiac death. In the occult phase, it is important to delay decompensation, to treat syncope and prevent sudden cardiac death (medication).
In the third phase, the clinical phase, clinical symptoms, e.g. lack of performance, dry cough/choking, increased abdominal circumference, increased breathing frequency, shortness of breath, movement reluctance and/or longer periods of rest in the affected dog.
At this stage, the DCM is now also recognisable by auscultation from heart sounds and/or cardiac arrhythmias, as well as by X-rays by e.g. Cardiomegaly, pulmonary oedema, thorax effusion and congestive heart failure.
In the ECG, ventricular extrasystoles (heart attacks outside the physiological rhythm with formation in one of the heart chambers), atrial fibrillation and forensic ventricular tachycardia (increased heart rate, which emanates from the heart chambers) also appear in this clinical stage.
Via heart ultrasound expansions of the chamber as well as the atrial, cardiac muscle weakness and a secondary mitral regurgitation (i.e. leakage of the mitral valve/left atrial valve) can be represented.
The clinical phase is the shortest phase of DCM.