Evidence exists that SAM of the mitral valve begins even before aortic valve opening and onset of ejection. If this is so, increased inotropy after the long diastole certainly plays a greater role in the increased obstruction than can be appreciated with the methodology available to us. Present attempts at better delineating this pre-ejection component of the SAM before and during CSP are being pursued. However, again, this component (increased force of contraction) cannot explain per se the different responses to CSP in those with HOCM and those with AS, whereas the concept of decreased afterload and its different effects on an anatomically stenotic aortic valve and a dynamic LV tract obstruction can.
Starlings law of the heart is problematic, too. Because of the intrinsic crudeness of M-mode LV endocardial measurements, the possibility of increased LV dimension (ie, increased preload) cannot be completely excluded. However, this too would not clearly explain the difference between AS and HOCM.
Besides the technical considerations noted above, this study was clearly not blinded read more online asthma inhalers. On-line data recording, using the electronic caliper as the signals appear on the video screen before and during CSF, introduced a certain bias; however, this could affect the exactitude of the change in pressure gradient, but not its direction nor its gross magnitude.
No control group of normal subjects was included in this study because preliminary studies had shown that CSP does not affect systolic murmur intensity to any great degree in such subjects.
Clinical Implications
The finding that CSP increases the murmur intensity in HOCM and not in AS provides a reasonable way of diagnosing HOCM at the bedside without the need of patient cooperation, and the present study provides the physiologic underpinning for this difference in responses. A potential caveat is that β-blockers and calcium-channel blockers tend to blunt the heart rate response to CSP, because of the basal bradycardia they produce. Other than this, however, application of CSP is indeed often useful in differentiating the two entities.