Developmental abnormalities of the aortic valve are frequently observed, with the bicuspid aortic valve being the most common congenital defect, affecting 0.9–1.3% of the population [7]. Other less common variants include unicuspid (0.02%), quadricuspid (0.008%–0.043%), and pentacuspid aortic valves. [7] Advances in echocardiography have facilitated non-invasive diagnosis of these abnormalities, which were previously often detected during surgery or at autopsy. In the short axis view, a QAV typically exhibits an “X” shape in diastole, in contrast to the “Y” pattern of a normal tricuspid valve or a single commissural line characteristic of a bicuspid valve. Our patient's TTE showed a single commissural pattern in diastole; however, on TEE it was confirmed to be QAV (Figs. 2 and 3).

Some pathophysiological mechanisms proposed that might alter the valve cusp number are irregular septation of the conotruncus, anomalous proliferation of mesenchymal ridges, or valve cusp division during its formation. However, as per the most accepted hypothesis, there is an invagination of the endothelial layer on the luminal side causing partition of one of the three-valve cushions during an early stage of valve development [8]. The functionality of a QAV usually remains normal until around 18 years of age, but it tends to deteriorate after the age of 40. There is a slight male predominance in cases of QAV. Clinical manifestations vary and depend on the functional status of the valve, ranging from asymptomatic to palpitations, chest pain, shortness of breath, sudden cardiac death, or features of advanced heart failure [3].

Observational data indicate that AR is more common than AS or ascending aortic valve enlargement in patients with QAV. Unequal cusp size and abnormal shear stress lead to progressive fibrosis and poor leaflet coaptation [8]. Approximately half of all QAV patients will eventually require surgical intervention [2]. Furthermore, one-third of individuals with QAV have other associated structural heart diseases, such as mitral or tricuspid valve prolapse, pulmonary valve stenosis, hypertrophic cardiomyopathy, atrial or ventricular septal defects, or coronary anomalies [1, 3].

Our case is the second reported instance of QAV with CHB in the absence of IE or aortic valve surgery. While CHB may occur due to IE-related abscess formation or infection extending from the aortic valve, these were absent in our patient [6]. Although congenital CHB is a possibility, the patient had never undergone an ECG before his syncopal episode and lived an active lifestyle without symptoms of fatigue. Aortic valve fibrosis and calcification which progresses to involve aortic root is a less studied cause of conduction pathway abnormalities and can be responsible for CHB in our case [9]. The right and non-coronary sinuses of Valsalva lie close to the superior interventricular septum and His bundle, and it may be that hemodynamic stress of spontaneous AR leads to dilatation of aortic annulus and surrounding structures. Unequal size of cusps with uneven distribution of stress was a postulated mechanism for these hemodynamic abnormalities, however, these can occur with equal size cusps as well [3]. Nearly half of patients with QAV will require valve surgery in their lifetime. During the surgical replacement of these valves, the surgical suture should be transitioned to a supra-annular location and anteriorly high within the membranous septum to avoid the development of CHB in the postoperative period [4].

Here we have reported a rare combination of two life-threatening conditions with CHB in a patient with QAV in the absence of IE or surgery. These QAVs are prone to hemodynamic stress leading to AR, AS, and aortic root dilatation. Also, they are at increased risk of IE necessitating surgical replacement. During surgery placement of suture is important to avoid post-operative CHB. After a permanent pacemaker, they need regular follow-ups for the development of hemodynamic abnormalities of AR, AS, and aortopathy due to underlying QAV. It is reasonable to repeat TTE every 2–3 years in patients with mild to moderate AR [10]. It is also important to note that QAV may be missed on TTE, and TEE is more informative.