Partial atrioventricular canal (PAVC) is a congenital heart malformation characterized by an atrial septal defect (ASD; ostium primum), clefts of mitral and occasionally tricuspid valves, two separate atrioventricular (AV) valve annuli and an intact ventricular septum. The typical symptoms of PAVC are impaired exercise capacity and exertional dyspnea.
PAVC accounts for 1-2% of all congenital heart malformations and its prevalence is estimated to be 1/5,000-1/2,500.
The age of onset is variable, but clinical features may not appear until later in life. The clinical presentation depends on the degree of mitral regurgitation and on the associated cardiac defects. The two most common clinical manifestations are impaired exercise capacity and exertional dyspnea. Additional features include palpitations, presyncope or syncope, angina, transient ischemic attack, bacterial endocarditis and sustained atrial arrhythmias (fibrillation and flutter, a previous history of atrial tachyarrhythmia may be observed in > 50 years old patients). Some patients may be asymptomatic. PAVC may be associated with RASopathies (particularly Noonan syndrome caused by mutations in PTPN11 and RAF1), Ellis Van Creveld and Down syndromes (see these terms).
PAVC is characterized by a common AV junction; a trileaflet (cleft) left AV valve (LAVV) guarding the left ventricular component of the common AV junction, comprised of the mural leaflet and the superior and inferior bridging leaflets; a defect in the atrial component of the AV septum; and an ''unwedged'' aorta (caused by the common AV orifice displacing anteriorly the aortic root). In contrast to the complete form, patients with PAVC have two separate AV valves, (resulting from fusion of the superior and inferior bridging leaflets), and no large intraventricular communication. Intermediate forms include a partial AV septal defect (AVSD) with a coexisting small and restrictive ventricular septal defect. CRELD1 (3p25.3), GATA4 (8p23.1-p22), GATA6 (18q11-q12) and NR2F2 (15q26) have been associated with a small fraction of PAVC cases. These genes encode developmental transcription factors that are critical for normal cardiac morphogenesis.
Diagnosis of PAVC is established by means of 2D-echocardiography, transesophageal echocardiography or cardiac catheterization (to assess pulmonary vascular resistance and status of the left AV valve and, in patients > 40 years, to exclude coexisting coronary arterial disease). An elevated pulmonary arterial pressure and moderate to severe left atrioventricular valve regurgitation may be observed. First-degree AV block, right bundle branch block, and a superior QRS axis may be noted on electrocardiogram.
PAVC may be is detectable prenatally by 4-chamber view screening during obstetric ultrasonography.
The early diagnosis of PAVC requires cardiological follow-up resulting in timely operative repair which involves closure of a primum ASD with an appropriately shaped patch through right atriotomy. Primary suture may be used for closing additional secundum defects. A pacemaker insertion may be required for complete AV block, which may spontaneously develop after repair. A continuous lifelong follow-up is recommended to avoid late complications. Symptoms free patients may be referred for PAVC repair because of a substantial left-to right atrial shunt (pulmonary to systemic flow ratio 1.8:1) and echocardiographic or angiographic evidence of right heart volume overload.
PAVC may be fatal (sudden death, congestive heart failure, pulmonary embolus, endocarditis) but long-term survival after repair of partial AVSD is possible. The elective age for repair of PAVC is 3-5 years, but some patients will not present until later in life. The later the repair is made, the more loss of ventricular function occurs. High morbidity and need for reoperation, often related to residual problems of the systemic AV valve or LAVV regurgitation may be observed.
Last update: September 2014
- Dr Maria Cristina DIGILIO