Microscopic systolic pressure alternans in human cardiomyopathy: noninvasive evaluation of a novel risk marker and correlation with microvolt T-wave alternans.

BACKGROUND: In patients with severe left ventricular (LV) dysfunction, visible pulsus alternans coincides with visible T-wave alternans (TWA), but a similar relationship has not been described for nonvisible microscopic systolic pressure alternans (MSPA) and microvolt TWA (MTWA).

OBJECTIVE: The purpose of this study was to determine the prevalence of MSPA and its relationship to MTWA in patients with cardiomyopathy.

METHODS: Using the spectral method, MSPA was measured from finger pressure during incremental atrial pacing and then validated against MSPA measured from the LV pressure in 12 patients. In 23 other patients with cardiomyopathy (LV ejection fraction <40%), noninvasive MSPA and MTWA were measured simultaneously during incremental atrial pacing.

RESULTS: MSPA (<1 mm Hg) was detected in 80% of patients with cardiomyopathy and in 43% of controls. The presence of finger MSPA showed 100% positive concordance with LV MSPA; however, finger MSPA was 20% larger due to peripheral augmentation. Finger MSPA was highly concordant (96% positive concordance and 90% negative concordance) with MTWA. The magnitudes of MSPA and MTWA showed a linear correlation (R = 0.66, P <.001), and the k value, a measure of signal-to-noise ratio, was significantly larger for MSPA compared to MTWA (108 ± 88 vs 24 ± 48, P <.001). Premature beats resulted in concordant and coincident changes in MSPA and MTWA. During follow-up (454 ± 274 days), 2 (8.6%) patients experienced ventricular tachycardia, and both manifested MSPA and MTWA during pacing at 600 ms.

CONCLUSION: MSPA can be detected noninvasively in patients with cardiomyopathy and is coupled to MTWA, suggesting a common mechanism. The high signal-to-noise ratio of MSPA may provide a novel robust metric of sudden cardiac death risk in these patients.