Hereditary rhythm disorder with complex ventricular arrhythmias (ventricular premature complexes, ventricular tachycardia) that can progress to syncope and sudden death in young dogs. Described in the Rhodesian Ridgeback with a familial pattern and associated with a variant in the QIL1 gene, with mitochondrial cardiomyopathy (altered mitochondrial cristae). It is a condition distinct from arrhythmias due to channelopathy and from human electrical syndromes (long QT, Brugada, CPVT).

Limited data. Cases described in specific Rhodesian Ridgeback lines; no reliable population frequencies have been published.

- Frequent and complex ventricular premature complexes on Holter\n- Polymorphic ventricular tachycardia\n- Syncope, especially with exercise or excitement\n- Sudden death in young dogs\n- Structurally normal heart on echocardiography in many cases\n- Greater expression in males described in some series

The condition was described in the Rhodesian Ridgeback in a family with a history of sudden death; genealogical analysis (Meurs et al., 2016) documented ventricular arrhythmias without structural lesion in several relatives. The subsequent genomic study identified a variant in the QIL1 gene associated with the arrhythmia and with mitochondrial alterations (Meurs et al., 2019). It is not a channelopathy and the described molecular basis has not been independently replicated.

- Perform a 24-h Holter on all breeding animals before mating\n- Do not mate animals with a history of complex ventricular arrhythmia or syncope\n- In litters with several affected siblings, do not repeat the parental cross\n- Repeat the Holter annually in at-risk lines during the first years of life

Differentiate from cardiomyopathies (dilated and arrhythmogenic right ventricular), from arrhythmias secondary to valve disease, dehydration or drugs, and from the equivalent human electrical syndromes (long QT, Brugada, CPVT). The 24-72 h Holter is the key diagnostic tool. Coordinate management with a veterinary cardiologist: some cases respond to antiarrhythmics (beta-blockers, sotalol). Without a specific molecular test, breeding advice is based on Holter and genealogy.

1. Meurs KM et al. 2016. Ventricular arrhythmias in Rhodesian Ridgebacks with a family history of sudden death and results of a pedigree analysis for potential inheritance patterns. J Am Vet Med Assoc. PMID: 27135669
2. Meurs KM et al. 2019. A QIL1 Variant Associated with Ventricular Arrhythmias and Sudden Cardiac Death in the Juvenile Rhodesian Ridgeback Dog. Genes. PMID: 30795627