Cardiac action potential to fail, then the heart could continue to beat, albeit at a lower rate (AVN= 40-60 beats per minute, purkinje fibres = 20-40 beats per minute). These pacemakers will keep a patient alive until the emergency team arrives. An example of premature ventricular contraction, is the classic athletic heart syndrome. Sustained training of athletes causes a cardiac adaptation where the resting SAN rate is lower (sometimes around 40 beats per minute). This can lead to atrioventricular block, where the signal from the SAN is impaired in its path to the ventricles. This leads to uncoordinated contractions between the atria and
Heart failure with preserved ejection fraction and lower ejection fractions. Cardiac output is dependent on stroke volume and heart rate. A significant portion (55-77%) of HFpEF patients are unable to increase heart rate to compensate for increased output demand (as in the setting of exercise); this is termed chronotropic incompetence. Combined with the characteristic deficit in stroke volume observed in HFpEF patients, many individuals display poor exercise tolerance. Non-simultaneous contraction of the left and right ventricle, dyssychrony, is present in up to 58% of HFpEF patients. However, dyssynchrony is also common in HFrEF and its role in HFpEF in particular remains obscure. While therapies for dyssynchrony,