Transient Bradycardia Induced by Carotid Sinus Pressure Increases Outflow Obstruction in Hypertrophic Obstructive Cardiomyopathy but Not in Valvular Aortic Stenosis: CSP: Effects on Heart Rate and MurmurWith the patient lying quietly in the left lateral decubitus position, gentle pressure was applied to the right carotid sinus during five or fewer cardiac cycles; pressure was subsequently applied to the left carotid sinus if pressure on the right did not slow the heart rate as monitored on the ECG Source antibiotics online. If necessary, firmer pressure or massage was then applied to the right carotid sinus. In all patients, heart rate was recorded; murmur intensity and characteristics were monitored with the stethoscope, recorded graphically on a commercially available phonocardiographic recorder, and graded on a six-point scale.
Two patients with DDD pacemakers were similarly studied before and after the pacemaker rate w^as slowed transiently with an external pacemaker programmer; CSP was not applied. Three additional patients with HOCM who underwent diagnostic catheterization were subjected to atrial pacing faster than the sinus rate. Pacing was either slowed or stopped and simultaneous LV and aortic pressures were recorded; again, no CSP was applied.
Statistical Analysis
Data are generally expressed as means±SDs. The paired Student’s t test was used to determine differences in heart rate, maximum velocity, and pressure gradients. No adjustment was deemed necessary for multiple comparisons since only two measurements were made (before and during CSP) in each group of patients.
Hypertrophic Obstructive Cardiomyopathy
In six of the 36 HOCM patients (17%), heart rate decreased by <5 beats/min with CSP. Murmur intensity and LV outflow maximum instantaneous pressure gradient also failed to change (Fig 1).
Heart rate decreased by >5 beats/min with CSP in the other 30 (83%) patients (83%)—from 78±15 to 63±14 beats/min. The LV outflow maximal instantaneous pressure gradient increased in 28 of these 30 patients (92%) (Fig 1). The murmur also increased by at least one grade out of six in 24 of these 28 patients (86%); in these 24 patients, the pressure gradient increased by at least 25%. The murmur did not increase appreciably in four patients, although the outflow pressure gradient did increase by 12% to 35%. In two patients, heart rate decreased but maximum outflow velocity and murmur intensity did not change.

Figure 1. Response of 36 patients with HOCM to the application of CSP.Figure 1. Response of 36 patients with HOCM to the application of CSP.