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Different effects of abnormal activation and myocardial disease on left ventricular ejection and filling times
1Department of Cardiology, Royal Brompton and Harefield NHS Trust, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK.
Insights
The Z ratio effectively separates abnormal ventricular activation from dilated cardiomyopathy effects. This metric aids in comparing pacing modes in heart disease patients.
Area of Science:
- Cardiology
- Cardiac Electrophysiology
- Echocardiography
Background:
- Abnormal ventricular activation is common in dilated cardiomyopathy, but its impact on cardiac timing is unclear.
- Distinguishing activation abnormalities from chamber dilation is crucial for accurate assessment.
Purpose of the Study:
- To evaluate the Z ratio (sum of left ventricular ejection and filling times to RR interval) for differentiating abnormal activation from dilated cardiomyopathy.
- To assess the Z ratio's utility in comparing hemodynamic effects of pacing modes.
Main Methods:
- Echocardiography (pulsed wave Doppler, M mode) measured left ventricular ejection/filling times and cavity size.
- Subjects included normal individuals, patients with left bundle branch block (LBBB), and dilated cardiomyopathy (with or without LBBB).
- Right ventricular pacing was performed in a subset of patients.
Main Results:
- The Z ratio was independent of heart rate (RR interval).
- Patients with LBBB or dilated cardiomyopathy with LBBB showed significantly lower Z ratios compared to normal subjects.
- Right ventricular pacing reduced the Z ratio in normal hearts but increased it in dilated cardiomyopathy with LBBB.
Conclusions:
- The Z ratio successfully dissociates the effects of abnormal ventricular activation and systolic dysfunction.
- It clearly differentiates left bundle branch block from right ventricular pacing effects.
- The Z ratio is a valuable tool for assessing hemodynamic impacts of pacing in cardiac disease.
Background:
Ventricular activation is often abnormal in patients with dilated cardiomyopathy, but its specific effects on timing remain undetermined.
Objective:
To investigate the use of the ratio of the sum of left ventricular ejection and filling times to the total RR interval (Z ratio) to dissociate the effects of abnormal activation from those of cavity dilatation.
Methods:
Subjects were 20 normal individuals, 11 patients with isolated left bundle branch block (LBBB, QRS duration > 120 ms), 17 with dilated cardiomyopathy and normal activation, and 23 with dilated cardiomyopathy and LBBB. An additional 30 patients (nine with normal ventricular systolic function and 21 with dilated cardiomyopathy) were studied before and after right ventricular pacing. Left ventricular ejection and filling times were measured by pulsed wave Doppler and cavity size by M mode echocardiography.
Results:
Z ratio was independent of RR interval in all groups. Mean (SD) Z ratio was 82 (10)% for normal subjects, 66 (10)% for isolated LBBB (p < 0.01 v normal), 77 (7)% for dilated cardiomyopathy without LBBB (NS v normal), and 61 (7)% for dilated cardiomyopathy with LBBB (p < 0.01 v normal). In the nine patients with normal left ventricular size and QRS duration, Z ratio fell from 88 (6)% in sinus rhythm to 77 (10)% with right ventricular pacing (p = 0.26). In the 21 patients with dilated cardiomyopathy and LBBB, Z ratio rose from 59 (10)% in sinus rhythm to 74 (9)% with right ventricular DDD pacing (p < 0.001).
Conclusions:
Z ratio dissociates the effects of abnormal ventricular activation and systolic disease. It also clearly differentiates right ventricular pacing from LBBB. It may thus be useful in comparing the haemodynamic effects of different pacing modes in patients with or without left ventricular disease.