Figure 1.
ECG traces (1 second) in a control animal (top) and in a representative aged animal displayed each month during the six-month study.
Figure 2.
Telemetry ECG time and frequency domain analysis.
Histograms of telemetry ECG basic electrophysiological parameters and frequency domain indexes of simpathovagal balance, evaluated from the 1st to the 6th month after radiotelemetry transmitter implantation of all animals. HF: High Frequency. LF: Low Frequency. * p<0.01 compared with control (ctrl).
Figure 3.
Impulse formation and conduction arrhythmias.
Telemetry ECG recordings (2 seconds) of representative arrhythmic events, observed during the six-month period, that belong to the groups of impulse formation arrhythmia (A: sinus pause; B: atrial extrasystoles; C: ventricular extrasystole) and impulse conduction arrhythmia (D: second degree atrioventricular (AV) block with junctional escape beat; E: phasic aberrant ventricular conduction). Numbers identify time intervals in ms.
Figure 4.
Histograms relating to the type (A) and the location (B) of arrhythmic events of control and aged animals which occurred during telemetry ECG recording. Number of arrhythmic events was evaluated on the ECGs from the 1st to the 6th month after radiotelemetry transmitter implantation, as compared to controls (ctrl).
Figure 5.
Sinus rhythm ventricular activations recorded in aged rats after the 6th month.
A: multiple breakthrough points (BTPs). B: single BTP. C: absence of BTP. Left panels: activation isochrone line maps. Numbers: activation times in ms from QRS onset; star: BTP site; dotted line, interventricular septum (IVS); black dot on the lower-right corner, reference point for epicardial orientation. Middle panels: 8×8 electrode array electrograms (EGs); vertical bar, maximum peak-to-peak EG amplitude (25 mV); horizontal bar, EG time scale (30 ms). Right panels: schematic view of the heart and epicardial electrode array position and orientation. PA, pulmonary artery; A, aorta; SVC, superior vena cava; RA, right atrial appendage; LA, left atrial appendage; RV, right ventricle; LV, left ventricle; dotted line, IVS; double arrowhead, epicardial fiber direction; square box, 8×8 electrode array with black dot for epicardial orientation (see above).
Figure 6.
Atrial myocardial interstitial fibrosis.
A: control heart section with no pathological interstitial collagen depositions; B: aged heart section with a focus of perivascular interstitial fibrosis (arrow); C: aged heart section with a focus of myocytolisis (arrow). Hematoxylin and Eosin staining. Original magnification: A and B ×10, C ×20 with scale bar in A and B 500 µm and in C 200 µm.