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Diminished contractile response to increased heart rate in intact human left ventricular hypertrophy. Systolic versus
C P Liu1, C T Ting, W Lawrence
1Department of Internal Medicine, Johns Hopkins Medical Institutions, Baltimore, Md 21287.
Insights
In patients with left ventricular hypertrophy (LVH), rapid heart rates impair systolic function, likely due to calcium handling issues, while diastolic function remains stable. This highlights a key difference in cardiac response to stress.
Area of Science:
- Cardiology
- Physiology
Background:
- Experimental studies suggest hypertrophied myocardium has impaired contractile responses at rapid heart rates.
- This study investigates if these abnormalities occur in human subjects with left ventricular hypertrophy (LVH) during physiological pacing.
Purpose of the Study:
- To determine if human subjects with LVH exhibit impaired systolic function under rapid pacing.
- To assess the link between systolic impairment and diastolic dysfunction during rate stress in LVH.
Main Methods:
- Studied 10 LVH patients and 8 controls using pressure-volume analysis with conductance catheters and micromanometers.
- Varied cardiac filling using atrial pacing (100, 120, 150 bpm) and analyzed single-beat force-interval data.
Main Results:
- LVH subjects had baseline diastolic dysfunction but normal systolic function compared to controls.
- Rapid pacing diminished the positive contractile response in LVH patients, unlike controls.
- LVH subjects showed altered potentiation post-pacing, suggesting calcium handling abnormalities, but diastolic function did not worsen.
Conclusions:
- Pacing stress induces systolic impairment in human LVH, superimposed on existing diastolic dysfunction.
- Abnormal calcium handling is a likely contributor to the observed systolic impairment in LVH.
- Diastolic function does not appear to be tightly linked to the rate-dependent systolic changes in LVH.
Background:
Experimental studies indicate that in addition to diastolic dysfunction, hypertrophied myocardium can display depressed contractile responses, particularly at rapid heart rates, compounding reserve limitations. This study tests whether such abnormalities exist in intact human subjects at physiological paced rates and, if so, whether they are linked to simultaneous rate-dependent deterioration in diastolic function.
Methods And Results:
Ten subjects with left ventricular hypertrophy (LVH) and 8 normal control subjects were studied. Most LVH patients presented with dyspnea and/or pulmonary edema and had concentric hypertrophy. Since rapid pacing simultaneously alters cardiac filling volumes and pressures, pressure-volume relation analysis was used to better define changes in contractile response. Patients were instrumented with a conductance catheter and micromanometer for pressure-volume data recording and a balloon occluder at the right atrial-inferior vena caval junction to vary filling and thus generate function relations. Data were obtained at baseline and at three atrial pacing rates (100, 120, 150 min-1). In addition, single-beat force-interval data were used to indirectly examine calcium cycling kinetics. LVH subjects demonstrated baseline diastolic abnormalities, including prolonged relaxation, elevated end-diastolic pressure, and reduced chamber compliance. However, systolic function was similar to that in control subjects. With rapid pacing, normal subjects displayed a positive contractile response, whereas this was markedly diminished in LVH subjects. With abrupt termination of pacing and return to slower sinus rhythm, LVH subjects displayed greater initial potentiation followed by a more rapid decline than control subjects, suggesting abnormalities of calcium handling. Despite contractile abnormalities, diastolic function did not further deteriorate with rapid pacing and thus did not appear to be tightly linked to the systolic changes.
Conclusions:
Pacing stress in intact human LVH can result in systolic impairment superimposed on preexisting but not worsened diastolic dysfunction. Abnormal calcium handling probably contributes prominently to this response.