Dobutamine-induced mechanical alternans is a marker of poor prognosis in idiopathic dilated cardiomyopathy

Baseline Blood Pressure and Left Ventricular Reverse Remodeling in Dilated Cardiomyopathy with Spontaneous Mechanical Alternans

Background Spontaneous mechanical alternans (MA), or pulsus alternans, has been observed in heart failure patients with hypertension or tachycardia for 150 years and is considered a sign of a poor prognosis. However, in some dilated cardiomyopathy (DCM) patients with MA, optimal medical therapy (OMT) brings left ventricular reverse remodeling (LVRR), a preferable prognostic indicator. This study examined the probability of LVRR in DCM patients with spontaneous MA and whether or not LVRR can be predicted by the baseline blood pressure or heart rate. Methods and Results Thirty-three newly diagnosed DCM patients were retrospectively examined. Spontaneous MA was observed during diagnostic cardiac catheterization in at least 1 of the pressure waveforms of the aorta, left ventricle, pulmonary artery, or right ventricle in 10 patients (30%) (MA-group). LVRR after OMT was achieved roughly equally in the MA group (6 of 10, 60%) and the non-MA group (12 of 23, 52%). In the MA group, those who achieved LVRR had a significantly higher baseline systolic aortic pressure (more than 120 mmHg in all 6 patients) than those who did not, although the baseline heart rate did not show a significant correlation with LVRR. In contrast, in the non-MA group, LVRR was unrelated to the baseline aortic pressure or heart rate. Conclusions The probability of LVRR in newly-diagnosed DCM patients with spontaneous MA was similar to that in those without spontaneous MA. Spontaneous MA may not necessarily be a sign of a poor prognosis if observed in patients with a preserved blood pressure.

Rate-dependent force, intracellular calcium, and action potential voltage alternans are modulated by sarcomere length and heart failure induced-remodeling of thin filament regulation in human heart failure: A myocyte modeling study

Microvolt T-wave alternans (MTWA) testing identifies heart failure patients at risk for lethal ventricular arrhythmias at near-resting heart rates (<110 beats per minute). Since pressure alternans occurs simultaneously with MTWA and has a higher signal to noise ratio, it may be a better predictor of arrhythmia, although the mechanism remains unknown. Therefore, we investigated the relationship between force alternans (FORCE-ALT), the cellular manifestation of pressure alternans, and action potential voltage alternans (APV-ALT), the cellular driver of MTWA. Our goal was to uncover the mechanisms linking APV-ALT and FORCE-ALT in failing human myocytes and to investigate how the link between those alternans was affected by pacing rate and by physiological conditions such as sarcomere length and heart failure induced-remodeling of mechanical parameters. To achieve this, a mechanically-based, strongly coupled human electromechanical myocyte model was constructed. Reducing the sarcoplasmic reticulum calcium uptake current (Iup) to 27% was incorporated to simulate abnormal calcium handling in human heart failure. Mechanical remodeling was incorporated to simulate altered thin filament activation and crossbridge (XB) cycling rates. A dynamical pacing protocol was used to investigate the development of intracellular calcium concentration ([Ca]i), voltage, and active force alternans at different pacing rates. FORCE-ALT only occurred in simulations incorporating reduced Iup, demonstrating that alternans in the intracellular calcium concentration (CA-ALT) induced FORCE-ALT. The magnitude of FORCE-ALT was found to be largest at clinically relevant pacing rates (<110 bpm), where APV-ALT was smallest. We found that the magnitudes of FORCE-ALT, CA-ALT and APV-ALT were altered by heart failure induced-remodeling of mechanical parameters and sarcomere length due to the presence of myofilament feedback. These findings provide important insight into the relationship between heart-failure-induced electrical and mechanical alternans and how they are altered by physiological conditions at near-resting heart rates.

Mechanical alternans is associated with mortality in acute hospitalized heart failure: prospective mechanical alternans study (MAS)

BACKGROUND

Acute hospitalized heart failure (AHHF) is associated with 40% to 50% risk of death or rehospitalization within 6 months after discharge. Timely (before hospital discharge) risk stratification of patients with AHHF is crucial. We hypothesized that mechanical alternans (MA) and T-wave alternans (TWA) are associated with postdischarge outcomes in patients with AHHF.

METHODS AND RESULTS

A prospective cohort study was conducted in the intensive cardiac care unit and enrolled 133 patients (59.6±15.7 years; 65% men) admitted with AHHF. Surface ECG and peripheral arterial blood pressure waveform via arterial line were recorded continuously during the intensive cardiac care unit stay. MA and TWA were measured by enhanced modified moving average method. All-cause death or heart transplant served as a combined primary end point. MA was observed in 28 patients (25%), whereas TWA was detected in 33 patients (33%). If present, MA was tightly coupled with TWA. Mean TWA amplitude was larger in patients with both TWA and MA when compared with patients with lone TWA (median, 37 [interquartile range, 26-61] versus 22 [21-23] μV; P=0.045). After a median of 10-month postdischarge, 42 (38%) patients died and 2 had heart transplants. MA was associated with the primary end point in univariable Cox model (hazard ratio, 1.84; 95% confidence interval, 1.00-3.40; P=0.05) and after adjustment for left ventricular ejection fraction, New York Heart Association HF class, and implanted implantable cardioverter defibrillator/cardiac resynchronization therapy defibrillator (hazard ratio, 2.12 95% confidence interval, 1.13-3.98; P=0.020). TWA without consideration of simultaneous MA was not significantly associated with primary end point (hazard ratio, 1.42; 95% confidence interval, 0.77-2.64; P=0.260).

CONCLUSIONS

MA is independently associated with outcomes in AHHF.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01557465.

Increased (99m)Tc-sestamibi washout reflects impaired myocardial contractile and relaxation reserve during dobutamine stress due to mitochondrial dysfunction in dilated cardiomyopathy patients

OBJECTIVES

This study investigated whether the technitium-99m sestamibi (MIBI) washout rate (WR) would predict mitochondrial damage and myocardial dysfunction in patients with dilated cardiomyopathy (DCM).

BACKGROUND

Myocardial mitochondrial damage reduces adenosine triphosphate production, resulting in myocardial dysfunction. Increased myocardial (99m)Tc-MIBI washout is reportedly caused by mitochondrial dysfunction.

METHODS

Twenty DCM patients (New York Heart Association functional class I-III) underwent myocardial (99m)Tc-MIBI scintigraphy and cardiac catheterization. Myocardial MIBI uptake was quantified as an early and delayed heart-to-mediastinum ratio, and WR was calculated. Maximum first derivative of left ventricular (LV) pressure (LV dP/dtmax) (an index of myocardial contractility) and LV pressure half-time (T1/2) (an index of myocardial relaxation) were calculated by the left ventricular pressure curve at baseline and during dobutamine infusion (15 μg/kg/min at maximum). Endomyocardial biopsy specimens were obtained for quantitative mRNA analysis and electron microscopy. The patients were divided into two groups as follows: 1) group A of 10 patients showing a WR ≤ 24.3% (median value) and 2) group B of 10 patients showing a WR >24.3%.

RESULTS

WR was significantly correlated with the percentage changes in LV dP/dtmax (%LV dP/dtmax) (r: -0.59; p = 0.01) and T1/2 (r: -0.57; p = 0.03) from baseline to peak dobutamine stress. The %LV dP/dtmax was significantly greater in group B than in group A. The abundance of mRNAs for mitochondrial electron transport-related enzymes was more significantly reduced in group B than in group A. Electron microscopy revealed significant correlations between WR and the severity of mitochondrial damage (r: 0.88; p = 0.048) and glycogen accumulation (r: 0.90; p = 0.044).

CONCLUSIONS

Increased (99m)Tc-MIBI washout may predict mitochondrial dysfunction and the impairment of myocardial contractile and relaxation reserves during dobutamine stress in DCM patients.

Mechanical alternans in human idiopathic dilated cardiomyopathy is caused with impaired force-frequency relationship and enhanced poststimulation potentiation

Mechanical alternans (MA) is frequently observed in patients with heart failure, and is a predictor of cardiac events. However, there have been controversies regarding the conditions and mechanisms of MA. To clarify heart rate-dependent contractile properties related to MA, we performed incremental right atrial pacing in 17 idiopathic dilated cardiomyopathy (DCM) patients and in six control patients. The maximal increase in left ventricular dP/dt during pacing-induced tachycardia was assessed as the force gain in the force-frequency relationship (FG-FFR), and the maximal increase in left ventricular dP/dt of the first post-pacing beats was examined as the force gain in poststimulation potentiation (FG-PSP). As a result, MA was induced in 9 DCM patients (DCM MA(+)) but not in the other 8 DCM patients (DCM MA(-)), and not in any of the control patients. DCM MA(+) had significantly lower FG-FFR (34.7 ± 40.9 vs 159.4 ± 103.9 mmHg/s, P = 0.0091) and higher FG-PSP (500.0 ± 96.8 vs 321.9 ± 94.9 mmHg/s, P = 0.0017), and accordingly a wider gap between FG-PSP and FG-FFR (465.3 ± 119.4 vs 162.5 ± 123.6 mmHg/s, P = 0.0001) than DCM MA(-) patients. These characteristics of DCM MA(+) showed clear contrasts to those of the control patients. In conclusion, MA is caused with an impaired force-frequency relationship despite significant poststimulation potentiation, suggesting that MA reflects ineffective utilization of the potentiated intrinsic force during tachycardia.

Comparison of bypass surgery with drug-eluting stents in diabetic patients with left main coronary stenosis

PURPOSE

Several studies have compared the effects of coronary stenting and coronary- artery bypass grafting (CABG) on left main coronary artery (LMCA) disease. However, there are limited data on the long-term outcomes of these two interventions in diabetic patients.

MATERIALS AND METHODS

We evaluated 56 patients with LMCA stenosis who underwent drug-eluting stent (DES) implantation and 116 patients who underwent CABG in a single hospital in China between January 2004 and December 2006. We compared long-term major adverse cardiac events (death; a "serious outcome" composite of death, myocardial infarction, or stroke; and target-vessel revascularization).

RESULTS

In-hospital (30-day) mortality was 0% for the DES group and 3.4% for the CABG group (p=0.31). There was no difference between the two groups in terms of risk of death [hazard ratio for stenting group, 0.49; 95% confidence interval (CI), 0.13-1.63; p=0.55] or risk of serious outcome (hazard ratio for DES group, 1.11; 95% CI, 0.39-1.45; p=0.47). The target-vessel revascularization rate was higher in the DES group than in the CABG group (hazard ratio, 3.67; 95% CI, 1.24-11.06; p=0.018).

CONCLUSION

In this cohort of diabetic patients with LMCA stenosis, there was no difference in composite endpoints between patients receiving DESs and those undergoing CABG. However, stenting was associated with higher rates of target-vessel revascularization than CABG. DES implantation in diabetic patients with LMCA disease was found to be at least as safe as CABG.