QT interval in cardiac amyloidosis

Electrocardiographic features and rhythm disorders in cardiac amyloidosis

Cardiac amyloidosis (CA) is an infiltrative cardiomyopathy caused by extracellular deposition of amyloid fibrils, mainly derived from transthyretin, either wild-type or hereditary variants, or immunoglobulin light chains misfolding. It is characterized by an increased left ventricular (LV) mass and diastolic dysfunction, which can lead to heart failure with preserved ejection fraction and/or conduction disturbances. The diagnosis is based on invasive pathology demonstration of amyloid deposits, or non-invasive criteria using advanced cardiovascular imaging techniques. Nevertheless, 12-lead electrocardiogram (ECG) remains of crucial importance in the assessment of patients with CA, since they can manifest peculiar features such as low QRS voltages, in discordance with the LV hypertrophy, but also pseudo-infarction patterns, sinus node dysfunction, atrioventricular blocks, premature supraventricular and ventricular beats, which support the presence of a myocardial disease. Great awareness of these common ECG characteristics of CA is needed to increase diagnostic performance and improve patient's outcome. In the present review, we discuss the current role of the ECG in the diagnosis and management of CA, focusing on the most common ECG abnormalities and rhythm disorders.

Noninvasive Mapping of the Electrophysiological Substrate in Cardiac Amyloidosis and Its Relationship to Structural Abnormalities

Background

The relationship between structural pathology and electrophysiological substrate in cardiac amyloidosis is unclear. Differences between light‐chain (AL) and transthyretin (ATTR) cardiac amyloidosis may have prognostic implications.

Methods and Results

ECG imaging and cardiac magnetic resonance studies were conducted in 21 cardiac amyloidosis patients (11 AL and 10 ATTR). Healthy volunteers were included as controls. With respect to ATTR, AL patients had lower amyloid volume (51.0/37.7 versus 73.7/16.4 mL, P=0.04), lower myocardial cell volume (42.6/19.1 versus 58.5/17.2 mL, P=0.021), and higher T1 (1172/64 versus 1109/80 ms, P=0.022) and T2 (53.4/2.9 versus 50.0/3.1 ms, P=0.003). ECG imaging revealed differences between cardiac amyloidosis and control patients in virtually all conduction‐repolarization parameters. With respect to ATTR, AL patients had lower epicardial signal amplitude (1.07/0.46 versus 1.83/1.26 mV, P=0.026), greater epicardial signal fractionation (P=0.019), and slightly higher dispersion of repolarization (187.6/65 versus 158.3/40 ms, P=0.062). No significant difference between AL and ATTR patients was found using the standard 12‐lead ECG. T1 correlated with epicardial signal amplitude (cc=−0.78), and extracellular volume with epicardial signal fractionation (cc=0.48) and repolarization time (cc=0.43). Univariate models based on single features from both cardiac magnetic resonance and ECG imaging classified AL and ATTR patients with an accuracy of 70% to 80%.

Conclusions

In this exploratory study cardiac amyloidosis was associated with ventricular conduction and repolarization abnormalities, which were more pronounced in AL than in ATTR. Combined ECG imaging–cardiac magnetic resonance analysis supports the hypothesis that additional mechanisms beyond infiltration may contribute to myocardial damage in AL amyloidosis. Further studies are needed to assess the clinical impact of this approach.

Diffuse interstitial fibrosis assessed by cardiac magnetic resonance is associated with dispersion of ventricular repolarization in patients with hypertrophic cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM) is characterized by myocyte hypertrophy, disarray, fibrosis, and increased risk for ventricular arrhythmias. Increased QT dispersion has been reported in patients with HCM, but the underlying mechanisms have not been completely elucidated. In this study, we examined the relationship between diffuse interstitial fibrosis, replacement fibrosis, QTc dispersion and ventricular arrhythmias in patients with HCM. We hypothesized that fibrosis would slow impulse propagation and increase dispersion of ventricular repolarization, resulting in increased QTc dispersion on surface electrocardiogram (ECG) and ventricular arrhythmias.

Methods

ECG and cardiac magnetic resonance (CMR) image analyses were performed retrospectively in 112 patients with a clinical diagnosis of HCM. Replacement fibrosis was assessed by measuring late gadolinium (Gd) enhancement (LGE), using a semi-automated threshold technique. Diffuse interstitial fibrosis was assessed by measuring T1 relaxation times after Gd administration, using the Look–Locker sequence. QTc dispersion was measured digitally in the septal/anterior (V1–V4), inferior (II, III, and aVF), and lateral (I, aVL, V5, and V6) lead groups on surface ECG.

Results

All patients had evidence of asymmetric septal hypertrophy. LGE was evident in 70 (63%) patients; the median T1 relaxation time was 411±38 ms. An inverse correlation was observed between T1 relaxation time and QTc dispersion in leads V1–V4 (p<0.001). Patients with HCM who developed sustained ventricular tachycardia had slightly higher probability of increased QTc dispersion in leads V1–V4 (odds ratio, 1.011 [1.004–1.0178, p=0.003). We found no correlation between presence and percentage of LGE and QTc dispersion.

Conclusion

Diffuse interstitial fibrosis is associated with increased dispersion of ventricular repolarization in leads, reflecting electrical activity in the hypertrophied septum. Interstitial fibrosis combined with ion channel/gap junction remodeling in the septum could lead to inhomogeneity of ventricular refractoriness, resulting in increased QTc dispersion in leads V1–V4.

Cardiac amyloidosis: a case report and therapeutic implications

Primary amyloidosis with cardiac involvement presenting as congestive heart failure (CHF) usually carries an unfavorable prognosis, with median survival of about 6 months. We are reporting a case of cardiac amyloidosis with an initial presentation of CHF in which the patient survived for more than 9 years. The prognosis most likely depends on the period of disease remission (i.e., negative serum and urine immunoelectrophoresis), which, in turn, depends on response to chemotherapy.

Comparison of usefulness between exercise capacity and echocardiographic indexes of left ventricular function in cardiac amyloidosis

In patients with primary systemic amyloidosis (AL), the echocardiographic assessment of ventricular function alone does not always correspond to patients' symptoms and functional status. Peak oxygen uptake and anaerobic threshold (AT), in contrast, constitute 2 objective, reliable and reproducible indicators of functional status in patients with circulatory failure. Thirty-two consecutive patients (mean age 50 +/- 13 years) with histologic evidence of systemic primary AL were studied (29 AL, 3 hereditary). There were 16 with echocardiographic features of cardiac infiltration (group I) and 16 without (group II). Twenty age- and gender-matched healthy subjects were also studied for comparison. Of the 32 patients, 12 were in New York Heart Association functional class I, 9 were in class II, and 11 were in class III. Each subject underwent 2-dimensional and Doppler echocardiography and cardiopulmonary exercise testing using a modified Bruce protocol. Left atrial (LA), left ventricular (LV) dimensions, wall thickness, and LV fractional shortening, as well as transmitral flow velocities and their E/A ratio were measured. Peak oxygen consumption (VO2max [ml/kg/min]), AT (ml/kg/min), and exercise duration (seconds) were also measured. VO2max and AT were lower in patients with AL than in controls (20.8 +/- 7.0 vs 35.0 +/- 8.5, p <0.001 and 13.1 +/- 3.7 vs 27.0 +/- 4.2, p <0.001, respectively). As a group, symptomatic patients had lower VO2max, AT, and exercise duration than those without symptoms (17.1 +/- 3.6 vs 27.0 +/- 6.9, p = 0.0001, 11.1 +/- 2.1 vs 16.2 +/- 3.6, p = 0.0001, and 489 +/- 235 vs 843 +/- 197, p = 0.0001, respectively), whereas LV dimensions only showed a small difference (p = 0.03). VO2max, AT, and exercise duration of patients in functional class I were higher than those in functional classes II and III (p = 0.01, p <0.05, and p = 0.007, respectively). Asymptomatic patients had lower VO2max, AT, and exercise duration than controls (p <0.0001). VO2max, AT, and exercise duration were poorly related to LA diameter, LV dimensions, fractional shortening, wall thickness, peak velocities of E and A waveforms, and E/A ratio. Patients with VO2max > 15 ml/kg/min had a better survival than patients with VO2max < 15 ml/kg/min. Thus, in patients with primary systemic AL, cardiorespiratory exercise testing is the preferred way of assessing functional capacity. Echocardiographic Doppler indexes at rest are not predictive of a patient's symptoms and exercise capacity. Furthermore, VO2max is a strong independent predictor of survival in these patients.

Compared effects of sotalol, flecainide and propafenone on ventricular repolarization in patients free of underlying structural heart disease

Antiarrhythmic drugs are known to affect the depolarization and repolarization time in a different fashion. The aim of the present study was to compare the effects of Sotalol, Flecainide and Propafenone on some common (QT, QTc, JT, JTc) or uncommon (QTc dispersion, T-peak to T-end interval) electrocardiographic parameters in order to evaluate the effects of these antiarrhythmic drugs on ventricular repolarization time both in terms of absolute values and of dispersion across the myocardium. The analysis of these antiarrhythmic drug effects was performed on the standard 12-lead electrocardiograms of 31 patients (17F and 14M, age 38.1+/-17 years, range 11-67 years) in the free-drug state and at the steady state after oral treatment with Sotalol (160 mg daily), Flecainide (200 mg daily) and Propafenone (450 mg daily). These drugs were prescribed, separately, to all the 31 patients, free of underlying structural heart disease, for the treatment of their atrio-ventricular nodal re-entry tachycardia. Data of the present study show that Sotalol, over the range prescribed, significantly prolongs ventricular repolarization index QT (P=0.001), JT (P=0.0001) and JTc (P=0.0001) values in an homogeneous fashion, as shown by the significant decrease in QTcD (P=0.019) and Tp-Te (P=0.01). On the contrary, Flecainide treatment was associated with an increase in QTcD (P=0.029), Tp-Te (0.0001), QT (P=0.001), QTc (P=0.0001) and QRS (P=0.0001), with no significant changes in JT and JTc. Propafenone, over the range prescribed, did not affect repolarization time, resulting only in a prolongation of depolarization time as expressed by the increase of QRS (P=0.0001).