The allometric model in chronic myocardial infarction

BACKGROUND: An allometric relationship between different electrocardiogram (ECG) parameters and infarcted ventricular mass was assessed in a myocardial infarction (MI) model in New Zealand rabbits. METHODS: A total of fifteen animals were used, out of which ten underwent left anterior descending coronary artery ligation to induce infarction (7–35% area). Myocardial infarction (MI) evolved and stabilized during a three month-period, after which, rabbits were sacrificed and the injured area was histologically confirmed. Right before sacrifice, ECGs were obtained to correlate several of its parameters to the infarcted mass. The latter was normalized after combining data from planimetry measurements and heart weight. The following ECG parameters were studied: RR and PR intervals, P-wave duration (P(D)), QRS duration (QRS(D)) and amplitude (QRS(A)), Q-wave (Q(A)), R-wave (R(A)) and S-wave (S(A)) amplitudes, T-wave peak amplitude (T(A)), the interval from the peak to the end of the T-wave (T(PE)), ST-segment deviation (ST(A)), QT interval (QT), corrected QT and JT intervals. Corrected QT was analyzed with different correction formulae, i.e., Bazett (QT(B)), Framingham (QT(FRA)), Fridericia (QT(FRI)), Hodge (QT(HO)) and Matsunaga (QT(MA)) and compared thereafter. The former variables and infarcted ventricular mass were then fitted to the allometric equation in terms of deviation from normality, in turn derived after ECGs in 5 healthy rabbits. RESULTS: Six variables (JT, QT(B), Q(A), S(A), T(A) and ST(A)) presented statistical differences among leads. QT showed the best allometric fit (r = 0.78), followed by T(A) (r = 0.77), ST(A) (r = 0.75), QT(FRA) (r = 0.72), T(PE) (r = 0.69), QT(FRI) (r = 0.68) and QT(MA) (r = 0.68). Corrected QT’s (QT(FRA), QT(FRI) and QT(MA)) performed worse than the uncorrected counterpart (QT), the former scaling allometrically with similar goodness of fits. CONCLUSIONS: QT, T(A), ST(A) and T(PE) could possibly be used to assess infarction extent in an old MI event through the allometric model as a first approach. Moreover, the T(PE) also produced a good allometric scaling, leading to the potential existence of promising allometric indexes to diagnose malignant arrhythmias.