**4. Results**

#### **4.1. Classification of IDCM patients on the basis of dobutamine-induced MA**

To identify on the basis of the classification by hemodynamic response to pacing or do‐ butamine stress testing, patients were classified into three groups: those who exhibited neither pacing- nor dobutamine-induced MA (n = 60, group N), those who manifested only pacing-induced MA (n = 20, group P), and those who developed both pacing- and dobutamine-induced MA (n = 10, group D). All patients who did not develop pacing-in‐ duced MA also did not exhibit dobutamine-induced MA. LV pressure waveforms during atrial pacing at 120 bpm or after dobutamine infusion at 10 µg kg–1 min–1 are shown for representative patients from each group (Fig. 1).

**Figure 1.** LV pressure waveforms during atrial pacing at 120 bpm and after infusion of dobutamine at a dose of 10 µg kg–1 min–1 in representative patients of three study groups. The traces represent the lead II electrocardiogram (ECG), LV pressure, and LV *dP*/*dt*. Both LV *dP*/*dt*max and LV *dP*/*dt*min showed alternating changes with LV pressure. Strong and weak beats are indicated by s and w, respectively.

#### **4.2. Baseline clinical data**

to be invented at the time when Traube reported his case. MA has been studied in the intact human and animal heart, in isolated muscle preparations, and most recently in isolated cardiac

The ability to induce MA by rapid driving frequencies appears to be a fundamental property of mammalian ventricular muscle. Experimental studies have shown that by varying the pacing cycle length over a wide range, it is possible to define a critical cycle length (threshold) for the induction of sustained MA.[3] Driving the heart at cycle lengths shorter than the threshold cycle length may increase the amplitude of the beat-to-

It is more prevalent and likely to be sustained, as exemplified by pacing-induced MA. Right atrial pacing was initiated at 80 beats per minute (bpm) and was increased in increments of 10 bpm. We selected steady-state LV pressure data for at least 2 min at the baseline and at each pacing rate for analysis.[4] We calculated the maximum first derivative of LV pressure (LV *dP/dt*max) as an index of contractility. To evaluate LV isovolumic relaxation, we computed *T*1/2, as previously described.[5] After the hemodynamic values had checked at baseline, dobuta‐ mine was infused intravenously at incremental doses of 5, 10, and 15 µg kg–1min–1 and hemodynamic measurements were performed at the end of each 5-min infusion period. MA was diagnosed if the pressure difference between the strong and weak beats was ≥4 mmHg

We prospectively followed up all patients for the occurrence of primary events, which were defined as cardiac death (from worsening heart failure or sudden death) or the unscheduled

To identify on the basis of the classification by hemodynamic response to pacing or do‐ butamine stress testing, patients were classified into three groups: those who exhibited neither pacing- nor dobutamine-induced MA (n = 60, group N), those who manifested only pacing-induced MA (n = 20, group P), and those who developed both pacing- and dobutamine-induced MA (n = 10, group D). All patients who did not develop pacing-in‐ duced MA also did not exhibit dobutamine-induced MA. LV pressure waveforms during

continuously in the analyzed LV pressure data, as previously described.[6]

readmission for decompensated heart failure. Noncardiac death was excluded.

**4.1. Classification of IDCM patients on the basis of dobutamine-induced MA**

muscle cells.

96 Cardiomyopathies

**3. Method**

**4. Results**

**2.2. Induction of MA**

beat oscillations in contraction strength.

**3.1. Pacing- and dobutamine- induced MA**

There were no significant differences in age and sex among the three groups of patients (Table 1). All patients were classified as NYHA functional class I or II at the time of cardiac catheter‐ ization. The LV ejection fraction (EF) in groups P and D was significantly lower than that in group N. There were also no significant differences in plasma brain natriuretic peptide (BNP) or norepinephrine levels among the three groups.

The abundance of phospholamban mRNA was significantly lower in group D than in group P. The SERCA2a/phospholamban mRNA ratio was significantly higher in group D than in groups N and P (Table 2). The probability of event-free survival in group D was significantly lower than that in groups N or P (P = 0.002) (Fig. 2).

**mRNA ratio Group N Group P Group D** SERCA2a/GAPDH 0.42 ± 0.15 0.41 ± 0.13 0.43 ± 0.13 Phospholamban/GAPDH 0.82 ± 0.45 1.01 ± 0.13 0.42 ± 0.24\* Ryanodine receptor 2/GAPDH 0.50 ± 0.19 0.53 ± 0.21 0.75 ± 0.17 SERCA2a/phospholamban 0.63 ± 0.31 0.59 ± 0.40 1.32 ± 0.95\*† SERCA2a/Na+-Ca2+ exchanger 0.57 ± 0.79 0.50 ± 0.56 0.27 ± 0.14

Dobutamine-Induced Mechanical Alternans http://dx.doi.org/10.5772/55003 99

**Table 2.** Quantitative RT-PCR analysis of the abundance of Ca2+-handling protein mRNAs in endomyocardial biopsy

Univariate analysis revealed that dobutamine-induced MA, pacing-induced MA, NYHA functional class, plasma BNP levels, mitral regurgitation, pulmonary artery wedge pres‐ sure, LV end-diastolic volume index, LV end-systolic volume index, LVEF, LV end-dia‐ stolic pressure and *T*½ were significant predictors of cardiac events (Table 3). Then, stepwise multivariate analysis identified dobutamine-induced MA (odds ratio, 4.05; 95% confidence interval, 1.35 to 12.2) as a significant independent predictor of cardiac events (Table 4). Both *T*1/2 (odds ratio, 1.079; 95% confidence interval, 1.003 to 1.161) and plasma BNP level (odds ratio, 1.002; 95% confidence interval, 1.0004 to 1.0038) were also signifi‐ cant independent predictors of cardiac events, but with smaller odds ratios than that of

**Parameter Event-free group Cardiac-event group**

**Univariate analysis**

**(n = 72) (n = 18 )**

Age (years) 50 ± 12 53 ± 14 0.34 Sex (M/F) 53 / 19 13 / 5 0.86

Body mass index (kg/m2) 24.4 ± 4.9 22.5 ± 2.6 0.15 NYHA functional class † 1.3 ± 0.5 1.6 ± 0.4 0.011 QRS duration (ms) 113 ± 27 112 ± 22 0.88 Beta blockers 55 (76%) 10 (56%) 0.58 Diuretics 52 (72%) 16 (89%) 0.88

4 / 68 6 / 12 0.0019

20 / 52 10 / 8 0.04

*P*

\**P* < 0.05 versus group P, †*P* < 0.05 versus group N.

dobutamine-induced MA.

Dobutamine-induced MA (group D/groups P and N)

Pacing-induced MA (groups D and P/group N)

**4.3. Univariate and multivariate analysis of cardiac events**

specimens.

**Figure 2.** Kaplan-Meier analysis of the cumulative probability of event-free survival of the 90 IDCM study patients. Car‐ diac events were defined as hospitalization due to worsening heart failure and cardiac death. The probability of eventfree survival in group D was significantly lower than that in groups P and N by the log-rank test (*P* = 0.002).


\**P* < 0.05 versus group N. Abbreviations not defined in text: ACE, angiotensin-converting enzyme; ARB, angiotensin-II receptor blocker; PAWP, pulmonary artery wedge pressure.

**Table 1.** Baseline clinical characteristics of patients in the three study groups.


\**P* < 0.05 versus group P, †*P* < 0.05 versus group N.

**Figure 2.** Kaplan-Meier analysis of the cumulative probability of event-free survival of the 90 IDCM study patients. Car‐ diac events were defined as hospitalization due to worsening heart failure and cardiac death. The probability of event-

**Characteristic Group N (n = 60) Group P (n = 20) Group D (n = 10)**

Age (years) 51 ± 12 50 ± 13 45 ± 11 Sex (M/F) 44 / 16 16 / 4 6 / 4

class II 28 (47%) 11 (55%) 5 (50%)

Diuretics 30 (50%) 17\* (85%) 9\* (90%)

LVEF (%) 38.9 ± 8.1 32.9 ± 9.6\* 30.3 ± 9.0\* Plasma BNP (pg/mL) 100 ± 173 179 ± 186 249 ± 262 Plasma norepinephrine (pg/mL) 440 ± 221 689 ± 764 664 ± 324

\**P* < 0.05 versus group N. Abbreviations not defined in text: ACE, angiotensin-converting enzyme; ARB, angiotensin-II

ACE inhibitors or ARBs 42 (70%) 19 (95%) 7 (70%) Beta blockers 22 (37%) 10 (50%) 5 (50%) PAWP (mmHg) 10.7 ± 4.7 14.6 ± 6.2\* 13.9 ± 7.2 Cardiac index (L min–1 m–2) 3.07 ± 0.55 2.83 ± 0.58 3.26 ± 0.66

NYHA functional class I 32 (53%) 9 (45%) 5 (50%)

free survival in group D was significantly lower than that in groups P and N by the log-rank test (*P* = 0.002).

Medication

98 Cardiomyopathies

receptor blocker; PAWP, pulmonary artery wedge pressure.

**Table 1.** Baseline clinical characteristics of patients in the three study groups.

**Table 2.** Quantitative RT-PCR analysis of the abundance of Ca2+-handling protein mRNAs in endomyocardial biopsy specimens.

#### **4.3. Univariate and multivariate analysis of cardiac events**

Univariate analysis revealed that dobutamine-induced MA, pacing-induced MA, NYHA functional class, plasma BNP levels, mitral regurgitation, pulmonary artery wedge pres‐ sure, LV end-diastolic volume index, LV end-systolic volume index, LVEF, LV end-dia‐ stolic pressure and *T*½ were significant predictors of cardiac events (Table 3). Then, stepwise multivariate analysis identified dobutamine-induced MA (odds ratio, 4.05; 95% confidence interval, 1.35 to 12.2) as a significant independent predictor of cardiac events (Table 4). Both *T*1/2 (odds ratio, 1.079; 95% confidence interval, 1.003 to 1.161) and plasma BNP level (odds ratio, 1.002; 95% confidence interval, 1.0004 to 1.0038) were also signifi‐ cant independent predictors of cardiac events, but with smaller odds ratios than that of dobutamine-induced MA.



ference in LVEF between patients who manifested only pacing-induced MA and those who developed both pacing- and dobutamine-induced MA, the probability of event-free survival in the latter group was significantly lower than that in the former. Multivariate analysis also revealed that the occurrence of dobutamine-induced MA was a significant

Dobutamine-Induced Mechanical Alternans http://dx.doi.org/10.5772/55003 101

Three general mechanisms have been proposed to account for the development of MA: alteration of action potential duration, impaired ventricular relaxation, and abnormal intra‐ cellular Ca2+-handling.[7] The low relative ratio of phospholamban to SERCA reduces the inhibition of SERCA and increases Ca2+-uptake; this enhances relaxation and contraction in the human atrium. However, humans lacking phospholamban develop lethal IDCM.[8] SERCA2a and ryanodine receptor 2 mRNA levels were similar in all three of our groups, whereas the relative ratio of SERCA to phospholamban was significantly higher in patients with pacingand dobutamine-induced MA than in those with only pacing-induced MA or with no MA. These results suggest that an imbalance between phospholamban and SERCA mRNA levels in the abundant Ca2+-handling proteins is associated with dobutamine-induced MA. Kobaya‐ shi et al. reported that the amounts of mRNAs for the β1-adrenergic receptor and SERCA2a in the myocardium were smaller in asymptomatic or mildly symptomatic IDCM patients with reduced adrenergic myocardial contractile reserve than in those with preserved adrenergic contractile reserves.[9] The occurrence of dobutamine-induced MA in our patients in the present study might also reflect abnormal β1-adrenergic receptor signaling in the myocardium. However, steady-state mRNA levels do not necessarily reflect the corresponding protein levels, in particular because both mRNA and protein synthesis or degradation may be altered

in the failing heart.[10, 11] Further studies are needed to elucidate these issues.

In patients with heart failure, dobutamine-induced MA is highly prevalent[6] and mechanical and visible T-wave alternans is detectable under tachycardia or catecholamine exposure.[4, 12] Dobutamine-induced MA may be attributed various factors, including an increase in the heart rate as a result of dobutamine infusion, impaired LV contraction, the influence of preload, and abnormal Ca2+ under pathophysiological conditions. Dobutamine is a β-stimulator that increases both heart rate and LV contraction. The increase in heart rate, but not that in LV contraction, is likely to be a trigger for the occurrence of dobutamine-induced MA. Therefore, the increased occurrence of dopamine-induced MA in heart failure patients might be related

In conclusion, the occurrence of dobutamine-induced MA is a potentially useful clinical predictor of poor prognosis in ambulatory patients with IDCM in sinus rhythm. Recent guidelines for the management of heart failure emphasize the need for earlier identification of and therapy for patients who are at high risk of developing heart failure or who have asymp‐

independent predictor of cardiac events.

to their poor myocardial contractile reserve.

**6. Conclusion**

**5.2. Mechanisms**

**Table 3.** Univariate of predictors of cardiac events.


**Table 4.** Multivariate analysis of predictors of cardiac events.
