Cannon waves occur classically, during ventricular ectopic beats .(Commonly irregular) regular cannon waves occur during Junctional tachycardias with 1:1 VA conduction
Cannon like wave may appear in the jugular vein if the VPDs is timed in a such a fashion ,the atrial systole occurs with a closed AV ( Tricuspid and mitral valve ) so the atrial contractile wave is reflected back into the veins.This not only happen in right atrium but also in the left atrium , but the cannon waves are sent into the pulmonary veins , which is not visible. As by tradition cannon waves are meant to be seen only in neck veins , we rarely realise the importance of such waves in the pulmonary veins.
There must be some significance for this abnormal pulmonary venous waves which travel in a retrograde fashion.In fact , with the advent of echocardiography, we realise pulmonary flow reversal is an important contribution for raised PCWP.
The dyspnea during multiple VPDs can be due to
1.Transient Mitral regurgitation and resultant elevation of PCWP.
2.Pulmonary venous cannon waves and it’s effect on J receptors.
3.Many of the intermittent episodes of dyspnea (Especially paroxysmal nocturnal dyspnea ) , other wise unexplained could be due to this pulmonary venous cannon waves.
4.It also need to be studied how this pulmonary venous cannon waves distribute themself into the 4 pulmonary veins.